From: Mike Rapoport rppt@linux.ibm.com
Hi,
@Andrew, this is based on v5.12-rc1, I can rebase whatever way you prefer.
This is an implementation of "secret" mappings backed by a file descriptor.
The file descriptor backing secret memory mappings is created using a dedicated memfd_secret system call The desired protection mode for the memory is configured using flags parameter of the system call. The mmap() of the file descriptor created with memfd_secret() will create a "secret" memory mapping. The pages in that mapping will be marked as not present in the direct map and will be present only in the page table of the owning mm.
Although normally Linux userspace mappings are protected from other users, such secret mappings are useful for environments where a hostile tenant is trying to trick the kernel into giving them access to other tenants mappings.
Additionally, in the future the secret mappings may be used as a mean to protect guest memory in a virtual machine host.
For demonstration of secret memory usage we've created a userspace library
https://git.kernel.org/pub/scm/linux/kernel/git/jejb/secret-memory-preloader...
that does two things: the first is act as a preloader for openssl to redirect all the OPENSSL_malloc calls to secret memory meaning any secret keys get automatically protected this way and the other thing it does is expose the API to the user who needs it. We anticipate that a lot of the use cases would be like the openssl one: many toolkits that deal with secret keys already have special handling for the memory to try to give them greater protection, so this would simply be pluggable into the toolkits without any need for user application modification.
Hiding secret memory mappings behind an anonymous file allows usage of the page cache for tracking pages allocated for the "secret" mappings as well as using address_space_operations for e.g. page migration callbacks.
The anonymous file may be also used implicitly, like hugetlb files, to implement mmap(MAP_SECRET) and use the secret memory areas with "native" mm ABIs in the future.
Removing of the pages from the direct map may cause its fragmentation on architectures that use large pages to map the physical memory which affects the system performance. However, the original Kconfig text for CONFIG_DIRECT_GBPAGES said that gigabyte pages in the direct map "... can improve the kernel's performance a tiny bit ..." (commit 00d1c5e05736 ("x86: add gbpages switches")) and the recent report [1] showed that "... although 1G mappings are a good default choice, there is no compelling evidence that it must be the only choice". Hence, it is sufficient to have secretmem disabled by default with the ability of a system administrator to enable it at boot time.
In addition, there is also a long term goal to improve management of the direct map.
[1] https://lore.kernel.org/linux-mm/213b4567-46ce-f116-9cdf-bbd0c884eb3c@linux....
v18: * rebase on v5.12-rc1 * merge kfence fix into the original patch * massage commit message of the patch introducing the memfd_secret syscall
v17: https://lore.kernel.org/lkml/20210208084920.2884-1-rppt@kernel.org * Remove pool of large pages backing secretmem allocations, per Michal Hocko * Add secretmem pages to unevictable LRU, per Michal Hocko * Use GFP_HIGHUSER as secretmem mapping mask, per Michal Hocko * Make secretmem an opt-in feature that is disabled by default
v16: https://lore.kernel.org/lkml/20210121122723.3446-1-rppt@kernel.org * Fix memory leak intorduced in v15 * Clean the data left from previous page user before handing the page to the userspace
v15: https://lore.kernel.org/lkml/20210120180612.1058-1-rppt@kernel.org * Add riscv/Kconfig update to disable set_memory operations for nommu builds (patch 3) * Update the code around add_to_page_cache() per Matthew's comments (patches 6,7) * Add fixups for build/checkpatch errors discovered by CI systems
v14: https://lore.kernel.org/lkml/20201203062949.5484-1-rppt@kernel.org * Finally s/mod_node_page_state/mod_lruvec_page_state/
v13: https://lore.kernel.org/lkml/20201201074559.27742-1-rppt@kernel.org * Added Reviewed-by, thanks Catalin and David * s/mod_node_page_state/mod_lruvec_page_state/ as Shakeel suggested
Older history: v12: https://lore.kernel.org/lkml/20201125092208.12544-1-rppt@kernel.org v11: https://lore.kernel.org/lkml/20201124092556.12009-1-rppt@kernel.org v10: https://lore.kernel.org/lkml/20201123095432.5860-1-rppt@kernel.org v9: https://lore.kernel.org/lkml/20201117162932.13649-1-rppt@kernel.org v8: https://lore.kernel.org/lkml/20201110151444.20662-1-rppt@kernel.org v7: https://lore.kernel.org/lkml/20201026083752.13267-1-rppt@kernel.org v6: https://lore.kernel.org/lkml/20200924132904.1391-1-rppt@kernel.org v5: https://lore.kernel.org/lkml/20200916073539.3552-1-rppt@kernel.org v4: https://lore.kernel.org/lkml/20200818141554.13945-1-rppt@kernel.org v3: https://lore.kernel.org/lkml/20200804095035.18778-1-rppt@kernel.org v2: https://lore.kernel.org/lkml/20200727162935.31714-1-rppt@kernel.org v1: https://lore.kernel.org/lkml/20200720092435.17469-1-rppt@kernel.org rfc-v2: https://lore.kernel.org/lkml/20200706172051.19465-1-rppt@kernel.org/ rfc-v1: https://lore.kernel.org/lkml/20200130162340.GA14232@rapoport-lnx/ rfc-v0: https://lore.kernel.org/lkml/1572171452-7958-1-git-send-email-rppt@kernel.or...
Mike Rapoport (9): mm: add definition of PMD_PAGE_ORDER mmap: make mlock_future_check() global riscv/Kconfig: make direct map manipulation options depend on MMU set_memory: allow set_direct_map_*_noflush() for multiple pages set_memory: allow querying whether set_direct_map_*() is actually enabled mm: introduce memfd_secret system call to create "secret" memory areas PM: hibernate: disable when there are active secretmem users arch, mm: wire up memfd_secret system call where relevant secretmem: test: add basic selftest for memfd_secret(2)
arch/arm64/include/asm/Kbuild | 1 - arch/arm64/include/asm/cacheflush.h | 6 - arch/arm64/include/asm/kfence.h | 2 +- arch/arm64/include/asm/set_memory.h | 17 ++ arch/arm64/include/uapi/asm/unistd.h | 1 + arch/arm64/kernel/machine_kexec.c | 1 + arch/arm64/mm/mmu.c | 6 +- arch/arm64/mm/pageattr.c | 23 +- arch/riscv/Kconfig | 4 +- arch/riscv/include/asm/set_memory.h | 4 +- arch/riscv/include/asm/unistd.h | 1 + arch/riscv/mm/pageattr.c | 8 +- arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/x86/include/asm/set_memory.h | 4 +- arch/x86/mm/pat/set_memory.c | 8 +- fs/dax.c | 11 +- include/linux/pgtable.h | 3 + include/linux/secretmem.h | 30 +++ include/linux/set_memory.h | 16 +- include/linux/syscalls.h | 1 + include/uapi/asm-generic/unistd.h | 6 +- include/uapi/linux/magic.h | 1 + kernel/power/hibernate.c | 5 +- kernel/power/snapshot.c | 4 +- kernel/sys_ni.c | 2 + mm/Kconfig | 3 + mm/Makefile | 1 + mm/gup.c | 10 + mm/internal.h | 3 + mm/mlock.c | 3 +- mm/mmap.c | 5 +- mm/secretmem.c | 261 +++++++++++++++++++ mm/vmalloc.c | 5 +- scripts/checksyscalls.sh | 4 + tools/testing/selftests/vm/.gitignore | 1 + tools/testing/selftests/vm/Makefile | 3 +- tools/testing/selftests/vm/memfd_secret.c | 296 ++++++++++++++++++++++ tools/testing/selftests/vm/run_vmtests.sh | 17 ++ 39 files changed, 726 insertions(+), 53 deletions(-) create mode 100644 arch/arm64/include/asm/set_memory.h create mode 100644 include/linux/secretmem.h create mode 100644 mm/secretmem.c create mode 100644 tools/testing/selftests/vm/memfd_secret.c
From: Mike Rapoport rppt@linux.ibm.com
The definition of PMD_PAGE_ORDER denoting the number of base pages in the second-level leaf page is already used by DAX and maybe handy in other cases as well.
Several architectures already have definition of PMD_ORDER as the size of second level page table, so to avoid conflict with these definitions use PMD_PAGE_ORDER name and update DAX respectively.
Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reviewed-by: David Hildenbrand david@redhat.com Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andy Lutomirski luto@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: Borislav Petkov bp@alien8.de Cc: Catalin Marinas catalin.marinas@arm.com Cc: Christopher Lameter cl@linux.com Cc: Dan Williams dan.j.williams@intel.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Elena Reshetova elena.reshetova@intel.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: James Bottomley jejb@linux.ibm.com Cc: "Kirill A. Shutemov" kirill@shutemov.name Cc: Matthew Wilcox willy@infradead.org Cc: Mark Rutland mark.rutland@arm.com Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Peter Zijlstra peterz@infradead.org Cc: Rick Edgecombe rick.p.edgecombe@intel.com Cc: Roman Gushchin guro@fb.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Tycho Andersen tycho@tycho.ws Cc: Will Deacon will@kernel.org Cc: Hagen Paul Pfeifer hagen@jauu.net Cc: Palmer Dabbelt palmerdabbelt@google.com --- fs/dax.c | 11 ++++------- include/linux/pgtable.h | 3 +++ 2 files changed, 7 insertions(+), 7 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c index b3d27fdc6775..12ff48bcee5b 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -49,9 +49,6 @@ static inline unsigned int pe_order(enum page_entry_size pe_size) #define PG_PMD_COLOUR ((PMD_SIZE >> PAGE_SHIFT) - 1) #define PG_PMD_NR (PMD_SIZE >> PAGE_SHIFT)
-/* The order of a PMD entry */ -#define PMD_ORDER (PMD_SHIFT - PAGE_SHIFT) - static wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];
static int __init init_dax_wait_table(void) @@ -98,7 +95,7 @@ static bool dax_is_locked(void *entry) static unsigned int dax_entry_order(void *entry) { if (xa_to_value(entry) & DAX_PMD) - return PMD_ORDER; + return PMD_PAGE_ORDER; return 0; }
@@ -1471,7 +1468,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp, { struct vm_area_struct *vma = vmf->vma; struct address_space *mapping = vma->vm_file->f_mapping; - XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, PMD_ORDER); + XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, PMD_PAGE_ORDER); unsigned long pmd_addr = vmf->address & PMD_MASK; bool write = vmf->flags & FAULT_FLAG_WRITE; bool sync; @@ -1530,7 +1527,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp, * entry is already in the array, for instance), it will return * VM_FAULT_FALLBACK. */ - entry = grab_mapping_entry(&xas, mapping, PMD_ORDER); + entry = grab_mapping_entry(&xas, mapping, PMD_PAGE_ORDER); if (xa_is_internal(entry)) { result = xa_to_internal(entry); goto fallback; @@ -1696,7 +1693,7 @@ dax_insert_pfn_mkwrite(struct vm_fault *vmf, pfn_t pfn, unsigned int order) if (order == 0) ret = vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn); #ifdef CONFIG_FS_DAX_PMD - else if (order == PMD_ORDER) + else if (order == PMD_PAGE_ORDER) ret = vmf_insert_pfn_pmd(vmf, pfn, FAULT_FLAG_WRITE); #endif else diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index cdfc4e9f253e..3562cccf84ee 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -28,6 +28,9 @@ #define USER_PGTABLES_CEILING 0UL #endif
+/* Number of base pages in a second level leaf page */ +#define PMD_PAGE_ORDER (PMD_SHIFT - PAGE_SHIFT) + /* * A page table page can be thought of an array like this: pXd_t[PTRS_PER_PxD] *
From: Mike Rapoport rppt@linux.ibm.com
It will be used by the upcoming secret memory implementation.
Signed-off-by: Mike Rapoport rppt@linux.ibm.com Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andy Lutomirski luto@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: Borislav Petkov bp@alien8.de Cc: Catalin Marinas catalin.marinas@arm.com Cc: Christopher Lameter cl@linux.com Cc: Dan Williams dan.j.williams@intel.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: David Hildenbrand david@redhat.com Cc: Elena Reshetova elena.reshetova@intel.com Cc: Hagen Paul Pfeifer hagen@jauu.net Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: James Bottomley jejb@linux.ibm.com Cc: "Kirill A. Shutemov" kirill@shutemov.name Cc: Mark Rutland mark.rutland@arm.com Cc: Matthew Wilcox willy@infradead.org Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Palmer Dabbelt palmerdabbelt@google.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Peter Zijlstra peterz@infradead.org Cc: Rick Edgecombe rick.p.edgecombe@intel.com Cc: Roman Gushchin guro@fb.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Tycho Andersen tycho@tycho.ws Cc: Will Deacon will@kernel.org --- mm/internal.h | 3 +++ mm/mmap.c | 5 ++--- 2 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/mm/internal.h b/mm/internal.h index 9902648f2206..8e9c660f33ca 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -353,6 +353,9 @@ static inline void munlock_vma_pages_all(struct vm_area_struct *vma) extern void mlock_vma_page(struct page *page); extern unsigned int munlock_vma_page(struct page *page);
+extern int mlock_future_check(struct mm_struct *mm, unsigned long flags, + unsigned long len); + /* * Clear the page's PageMlocked(). This can be useful in a situation where * we want to unconditionally remove a page from the pagecache -- e.g., diff --git a/mm/mmap.c b/mm/mmap.c index 3f287599a7a3..f989aa170de4 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1346,9 +1346,8 @@ static inline unsigned long round_hint_to_min(unsigned long hint) return hint; }
-static inline int mlock_future_check(struct mm_struct *mm, - unsigned long flags, - unsigned long len) +int mlock_future_check(struct mm_struct *mm, unsigned long flags, + unsigned long len) { unsigned long locked, lock_limit;
From: Mike Rapoport rppt@linux.ibm.com
ARCH_HAS_SET_DIRECT_MAP and ARCH_HAS_SET_MEMORY configuration options have no meaning when CONFIG_MMU is disabled and there is no point to enable them for the nommu case.
Add an explicit dependency on MMU for these options.
Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reported-by: kernel test robot lkp@intel.com --- arch/riscv/Kconfig | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 85d626b8ce5e..87ccc29fc31d 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -25,8 +25,8 @@ config RISCV select ARCH_HAS_KCOV select ARCH_HAS_MMIOWB select ARCH_HAS_PTE_SPECIAL - select ARCH_HAS_SET_DIRECT_MAP - select ARCH_HAS_SET_MEMORY + select ARCH_HAS_SET_DIRECT_MAP if MMU + select ARCH_HAS_SET_MEMORY if MMU select ARCH_HAS_STRICT_KERNEL_RWX if MMU select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
From: Mike Rapoport rppt@linux.ibm.com
The underlying implementations of set_direct_map_invalid_noflush() and set_direct_map_default_noflush() allow updating multiple contiguous pages at once.
Add numpages parameter to set_direct_map_*_noflush() to expose this ability with these APIs.
Signed-off-by: Mike Rapoport rppt@linux.ibm.com Acked-by: Catalin Marinas catalin.marinas@arm.com [arm64] Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andy Lutomirski luto@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: Borislav Petkov bp@alien8.de Cc: Christopher Lameter cl@linux.com Cc: Dan Williams dan.j.williams@intel.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: David Hildenbrand david@redhat.com Cc: Elena Reshetova elena.reshetova@intel.com Cc: Hagen Paul Pfeifer hagen@jauu.net Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: James Bottomley jejb@linux.ibm.com Cc: "Kirill A. Shutemov" kirill@shutemov.name Cc: Mark Rutland mark.rutland@arm.com Cc: Matthew Wilcox willy@infradead.org Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Palmer Dabbelt palmerdabbelt@google.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Peter Zijlstra peterz@infradead.org Cc: Rick Edgecombe rick.p.edgecombe@intel.com Cc: Roman Gushchin guro@fb.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Tycho Andersen tycho@tycho.ws Cc: Will Deacon will@kernel.org --- arch/arm64/include/asm/cacheflush.h | 4 ++-- arch/arm64/mm/pageattr.c | 10 ++++++---- arch/riscv/include/asm/set_memory.h | 4 ++-- arch/riscv/mm/pageattr.c | 8 ++++---- arch/x86/include/asm/set_memory.h | 4 ++-- arch/x86/mm/pat/set_memory.c | 8 ++++---- include/linux/set_memory.h | 4 ++-- kernel/power/snapshot.c | 4 ++-- mm/vmalloc.c | 5 +++-- 9 files changed, 27 insertions(+), 24 deletions(-)
diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h index 52e5c1623224..ace2c3d7ae7e 100644 --- a/arch/arm64/include/asm/cacheflush.h +++ b/arch/arm64/include/asm/cacheflush.h @@ -133,8 +133,8 @@ static __always_inline void __flush_icache_all(void)
int set_memory_valid(unsigned long addr, int numpages, int enable);
-int set_direct_map_invalid_noflush(struct page *page); -int set_direct_map_default_noflush(struct page *page); +int set_direct_map_invalid_noflush(struct page *page, int numpages); +int set_direct_map_default_noflush(struct page *page, int numpages); bool kernel_page_present(struct page *page);
#include <asm-generic/cacheflush.h> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c index 92eccaf595c8..b53ef37bf95a 100644 --- a/arch/arm64/mm/pageattr.c +++ b/arch/arm64/mm/pageattr.c @@ -148,34 +148,36 @@ int set_memory_valid(unsigned long addr, int numpages, int enable) __pgprot(PTE_VALID)); }
-int set_direct_map_invalid_noflush(struct page *page) +int set_direct_map_invalid_noflush(struct page *page, int numpages) { struct page_change_data data = { .set_mask = __pgprot(0), .clear_mask = __pgprot(PTE_VALID), }; + unsigned long size = PAGE_SIZE * numpages;
if (!debug_pagealloc_enabled() && !rodata_full) return 0;
return apply_to_page_range(&init_mm, (unsigned long)page_address(page), - PAGE_SIZE, change_page_range, &data); + size, change_page_range, &data); }
-int set_direct_map_default_noflush(struct page *page) +int set_direct_map_default_noflush(struct page *page, int numpages) { struct page_change_data data = { .set_mask = __pgprot(PTE_VALID | PTE_WRITE), .clear_mask = __pgprot(PTE_RDONLY), }; + unsigned long size = PAGE_SIZE * numpages;
if (!debug_pagealloc_enabled() && !rodata_full) return 0;
return apply_to_page_range(&init_mm, (unsigned long)page_address(page), - PAGE_SIZE, change_page_range, &data); + size, change_page_range, &data); }
#ifdef CONFIG_DEBUG_PAGEALLOC diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h index 6887b3d9f371..018e26732940 100644 --- a/arch/riscv/include/asm/set_memory.h +++ b/arch/riscv/include/asm/set_memory.h @@ -26,8 +26,8 @@ static inline void protect_kernel_text_data(void) {} static inline int set_memory_rw_nx(unsigned long addr, int numpages) { return 0; } #endif
-int set_direct_map_invalid_noflush(struct page *page); -int set_direct_map_default_noflush(struct page *page); +int set_direct_map_invalid_noflush(struct page *page, int numpages); +int set_direct_map_default_noflush(struct page *page, int numpages); bool kernel_page_present(struct page *page);
#endif /* __ASSEMBLY__ */ diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c index 5e49e4b4a4cc..9618181b70be 100644 --- a/arch/riscv/mm/pageattr.c +++ b/arch/riscv/mm/pageattr.c @@ -156,11 +156,11 @@ int set_memory_nx(unsigned long addr, int numpages) return __set_memory(addr, numpages, __pgprot(0), __pgprot(_PAGE_EXEC)); }
-int set_direct_map_invalid_noflush(struct page *page) +int set_direct_map_invalid_noflush(struct page *page, int numpages) { int ret; unsigned long start = (unsigned long)page_address(page); - unsigned long end = start + PAGE_SIZE; + unsigned long end = start + PAGE_SIZE * numpages; struct pageattr_masks masks = { .set_mask = __pgprot(0), .clear_mask = __pgprot(_PAGE_PRESENT) @@ -173,11 +173,11 @@ int set_direct_map_invalid_noflush(struct page *page) return ret; }
-int set_direct_map_default_noflush(struct page *page) +int set_direct_map_default_noflush(struct page *page, int numpages) { int ret; unsigned long start = (unsigned long)page_address(page); - unsigned long end = start + PAGE_SIZE; + unsigned long end = start + PAGE_SIZE * numpages; struct pageattr_masks masks = { .set_mask = PAGE_KERNEL, .clear_mask = __pgprot(0) diff --git a/arch/x86/include/asm/set_memory.h b/arch/x86/include/asm/set_memory.h index 4352f08bfbb5..6224cb291f6c 100644 --- a/arch/x86/include/asm/set_memory.h +++ b/arch/x86/include/asm/set_memory.h @@ -80,8 +80,8 @@ int set_pages_wb(struct page *page, int numpages); int set_pages_ro(struct page *page, int numpages); int set_pages_rw(struct page *page, int numpages);
-int set_direct_map_invalid_noflush(struct page *page); -int set_direct_map_default_noflush(struct page *page); +int set_direct_map_invalid_noflush(struct page *page, int numpages); +int set_direct_map_default_noflush(struct page *page, int numpages); bool kernel_page_present(struct page *page);
extern int kernel_set_to_readonly; diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 16f878c26667..d157fd617c99 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -2184,14 +2184,14 @@ static int __set_pages_np(struct page *page, int numpages) return __change_page_attr_set_clr(&cpa, 0); }
-int set_direct_map_invalid_noflush(struct page *page) +int set_direct_map_invalid_noflush(struct page *page, int numpages) { - return __set_pages_np(page, 1); + return __set_pages_np(page, numpages); }
-int set_direct_map_default_noflush(struct page *page) +int set_direct_map_default_noflush(struct page *page, int numpages) { - return __set_pages_p(page, 1); + return __set_pages_p(page, numpages); }
#ifdef CONFIG_DEBUG_PAGEALLOC diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h index fe1aa4e54680..c650f82db813 100644 --- a/include/linux/set_memory.h +++ b/include/linux/set_memory.h @@ -15,11 +15,11 @@ static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; } #endif
#ifndef CONFIG_ARCH_HAS_SET_DIRECT_MAP -static inline int set_direct_map_invalid_noflush(struct page *page) +static inline int set_direct_map_invalid_noflush(struct page *page, int numpages) { return 0; } -static inline int set_direct_map_default_noflush(struct page *page) +static inline int set_direct_map_default_noflush(struct page *page, int numpages) { return 0; } diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c index d63560e1cf87..64b7aab9aee4 100644 --- a/kernel/power/snapshot.c +++ b/kernel/power/snapshot.c @@ -86,7 +86,7 @@ static inline void hibernate_restore_unprotect_page(void *page_address) {} static inline void hibernate_map_page(struct page *page) { if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) { - int ret = set_direct_map_default_noflush(page); + int ret = set_direct_map_default_noflush(page, 1);
if (ret) pr_warn_once("Failed to remap page\n"); @@ -99,7 +99,7 @@ static inline void hibernate_unmap_page(struct page *page) { if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) { unsigned long addr = (unsigned long)page_address(page); - int ret = set_direct_map_invalid_noflush(page); + int ret = set_direct_map_invalid_noflush(page, 1);
if (ret) pr_warn_once("Failed to remap page\n"); diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 4f5f8c907897..8ab83fbecadd 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2195,13 +2195,14 @@ struct vm_struct *remove_vm_area(const void *addr) }
static inline void set_area_direct_map(const struct vm_struct *area, - int (*set_direct_map)(struct page *page)) + int (*set_direct_map)(struct page *page, + int numpages)) { int i;
for (i = 0; i < area->nr_pages; i++) if (page_address(area->pages[i])) - set_direct_map(area->pages[i]); + set_direct_map(area->pages[i], 1); }
/* Handle removing and resetting vm mappings related to the vm_struct. */
From: Mike Rapoport rppt@linux.ibm.com
On arm64, set_direct_map_*() functions may return 0 without actually changing the linear map. This behaviour can be controlled using kernel parameters, so we need a way to determine at runtime whether calls to set_direct_map_invalid_noflush() and set_direct_map_default_noflush() have any effect.
Extend set_memory API with can_set_direct_map() function that allows checking if calling set_direct_map_*() will actually change the page table, replace several occurrences of open coded checks in arm64 with the new function and provide a generic stub for architectures that always modify page tables upon calls to set_direct_map APIs.
[arnd@arndb.de: arm64: kfence: fix header inclusion ]
Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reviewed-by: Catalin Marinas catalin.marinas@arm.com Reviewed-by: David Hildenbrand david@redhat.com Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andy Lutomirski luto@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: Borislav Petkov bp@alien8.de Cc: Christopher Lameter cl@linux.com Cc: Dan Williams dan.j.williams@intel.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Elena Reshetova elena.reshetova@intel.com Cc: Hagen Paul Pfeifer hagen@jauu.net Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: James Bottomley jejb@linux.ibm.com Cc: "Kirill A. Shutemov" kirill@shutemov.name Cc: Mark Rutland mark.rutland@arm.com Cc: Matthew Wilcox willy@infradead.org Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Palmer Dabbelt palmerdabbelt@google.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Peter Zijlstra peterz@infradead.org Cc: Rick Edgecombe rick.p.edgecombe@intel.com Cc: Roman Gushchin guro@fb.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Tycho Andersen tycho@tycho.ws Cc: Will Deacon will@kernel.org --- arch/arm64/include/asm/Kbuild | 1 - arch/arm64/include/asm/cacheflush.h | 6 ------ arch/arm64/include/asm/kfence.h | 2 +- arch/arm64/include/asm/set_memory.h | 17 +++++++++++++++++ arch/arm64/kernel/machine_kexec.c | 1 + arch/arm64/mm/mmu.c | 6 +++--- arch/arm64/mm/pageattr.c | 13 +++++++++---- include/linux/set_memory.h | 12 ++++++++++++ 8 files changed, 43 insertions(+), 15 deletions(-) create mode 100644 arch/arm64/include/asm/set_memory.h
diff --git a/arch/arm64/include/asm/Kbuild b/arch/arm64/include/asm/Kbuild index 07ac208edc89..73aa25843f65 100644 --- a/arch/arm64/include/asm/Kbuild +++ b/arch/arm64/include/asm/Kbuild @@ -3,5 +3,4 @@ generic-y += early_ioremap.h generic-y += mcs_spinlock.h generic-y += qrwlock.h generic-y += qspinlock.h -generic-y += set_memory.h generic-y += user.h diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h index ace2c3d7ae7e..4e3c13799735 100644 --- a/arch/arm64/include/asm/cacheflush.h +++ b/arch/arm64/include/asm/cacheflush.h @@ -131,12 +131,6 @@ static __always_inline void __flush_icache_all(void) dsb(ish); }
-int set_memory_valid(unsigned long addr, int numpages, int enable); - -int set_direct_map_invalid_noflush(struct page *page, int numpages); -int set_direct_map_default_noflush(struct page *page, int numpages); -bool kernel_page_present(struct page *page); - #include <asm-generic/cacheflush.h>
#endif /* __ASM_CACHEFLUSH_H */ diff --git a/arch/arm64/include/asm/kfence.h b/arch/arm64/include/asm/kfence.h index d061176d57ea..aa855c6a0ae6 100644 --- a/arch/arm64/include/asm/kfence.h +++ b/arch/arm64/include/asm/kfence.h @@ -8,7 +8,7 @@ #ifndef __ASM_KFENCE_H #define __ASM_KFENCE_H
-#include <asm/cacheflush.h> +#include <asm/set_memory.h>
static inline bool arch_kfence_init_pool(void) { return true; }
diff --git a/arch/arm64/include/asm/set_memory.h b/arch/arm64/include/asm/set_memory.h new file mode 100644 index 000000000000..ecb6b0f449ab --- /dev/null +++ b/arch/arm64/include/asm/set_memory.h @@ -0,0 +1,17 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +#ifndef _ASM_ARM64_SET_MEMORY_H +#define _ASM_ARM64_SET_MEMORY_H + +#include <asm-generic/set_memory.h> + +bool can_set_direct_map(void); +#define can_set_direct_map can_set_direct_map + +int set_memory_valid(unsigned long addr, int numpages, int enable); + +int set_direct_map_invalid_noflush(struct page *page, int numpages); +int set_direct_map_default_noflush(struct page *page, int numpages); +bool kernel_page_present(struct page *page); + +#endif /* _ASM_ARM64_SET_MEMORY_H */ diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c index 90a335c74442..0ec94e718724 100644 --- a/arch/arm64/kernel/machine_kexec.c +++ b/arch/arm64/kernel/machine_kexec.c @@ -11,6 +11,7 @@ #include <linux/kernel.h> #include <linux/kexec.h> #include <linux/page-flags.h> +#include <linux/set_memory.h> #include <linux/smp.h>
#include <asm/cacheflush.h> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 3802cfbdd20d..9243ea9f4e9f 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -22,6 +22,7 @@ #include <linux/io.h> #include <linux/mm.h> #include <linux/vmalloc.h> +#include <linux/set_memory.h>
#include <asm/barrier.h> #include <asm/cputype.h> @@ -492,7 +493,7 @@ static void __init map_mem(pgd_t *pgdp) int flags = 0; u64 i;
- if (rodata_full || crash_mem_map || debug_pagealloc_enabled()) + if (can_set_direct_map() || crash_mem_map) flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
/* @@ -1470,8 +1471,7 @@ int arch_add_memory(int nid, u64 start, u64 size, * KFENCE requires linear map to be mapped at page granularity, so that * it is possible to protect/unprotect single pages in the KFENCE pool. */ - if (rodata_full || debug_pagealloc_enabled() || - IS_ENABLED(CONFIG_KFENCE)) + if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE)) flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
__create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start), diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c index b53ef37bf95a..d505172265b0 100644 --- a/arch/arm64/mm/pageattr.c +++ b/arch/arm64/mm/pageattr.c @@ -19,6 +19,11 @@ struct page_change_data {
bool rodata_full __ro_after_init = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED);
+bool can_set_direct_map(void) +{ + return rodata_full || debug_pagealloc_enabled(); +} + static int change_page_range(pte_t *ptep, unsigned long addr, void *data) { struct page_change_data *cdata = data; @@ -156,7 +161,7 @@ int set_direct_map_invalid_noflush(struct page *page, int numpages) }; unsigned long size = PAGE_SIZE * numpages;
- if (!debug_pagealloc_enabled() && !rodata_full) + if (!can_set_direct_map()) return 0;
return apply_to_page_range(&init_mm, @@ -172,7 +177,7 @@ int set_direct_map_default_noflush(struct page *page, int numpages) }; unsigned long size = PAGE_SIZE * numpages;
- if (!debug_pagealloc_enabled() && !rodata_full) + if (!can_set_direct_map()) return 0;
return apply_to_page_range(&init_mm, @@ -183,7 +188,7 @@ int set_direct_map_default_noflush(struct page *page, int numpages) #ifdef CONFIG_DEBUG_PAGEALLOC void __kernel_map_pages(struct page *page, int numpages, int enable) { - if (!debug_pagealloc_enabled() && !rodata_full) + if (!can_set_direct_map()) return;
set_memory_valid((unsigned long)page_address(page), numpages, enable); @@ -208,7 +213,7 @@ bool kernel_page_present(struct page *page) pte_t *ptep; unsigned long addr = (unsigned long)page_address(page);
- if (!debug_pagealloc_enabled() && !rodata_full) + if (!can_set_direct_map()) return true;
pgdp = pgd_offset_k(addr); diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h index c650f82db813..7b4b6626032d 100644 --- a/include/linux/set_memory.h +++ b/include/linux/set_memory.h @@ -28,7 +28,19 @@ static inline bool kernel_page_present(struct page *page) { return true; } +#else /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */ +/* + * Some architectures, e.g. ARM64 can disable direct map modifications at + * boot time. Let them overrive this query. + */ +#ifndef can_set_direct_map +static inline bool can_set_direct_map(void) +{ + return true; +} +#define can_set_direct_map can_set_direct_map #endif +#endif /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */
#ifndef set_mce_nospec static inline int set_mce_nospec(unsigned long pfn, bool unmap)
From: Mike Rapoport rppt@linux.ibm.com
Introduce "memfd_secret" system call with the ability to create memory areas visible only in the context of the owning process and not mapped not only to other processes but in the kernel page tables as well.
The secretmem feature is off by default and the user must explicitly enable it at the boot time.
Once secretmem is enabled, the user will be able to create a file descriptor using the memfd_secret() system call. The memory areas created by mmap() calls from this file descriptor will be unmapped from the kernel direct map and they will be only mapped in the page table of the processes that have access to the file descriptor.
The file descriptor based memory has several advantages over the "traditional" mm interfaces, such as mlock(), mprotect(), madvise(). File descriptor approach allows explict and controlled sharing of the memory areas, it allows to seal the operations. Besides, file descriptor based memory paves the way for VMMs to remove the secret memory range from the userpace hipervisor process, for instance QEMU. Andy Lutomirski says:
"Getting fd-backed memory into a guest will take some possibly major work in the kernel, but getting vma-backed memory into a guest without mapping it in the host user address space seems much, much worse."
memfd_secret() is made a dedicated system call rather than an extention to memfd_create() because it's purpose is to allow the user to create more secure memory mappings rather than to simply allow file based access to the memory. Nowadays a new system call cost is negligible while it is way simpler for userspace to deal with a clear-cut system calls than with a multiplexer or an overloaded syscall. Moreover, the initial implementation of memfd_secret() is completely distinct from memfd_create() so there is no much sense in overloading memfd_create() to begin with. If there will be a need for code sharing between these implementation it can be easily achieved without a need to adjust user visible APIs.
The secret memory remains accessible in the process context using uaccess primitives, but it is not exposed to the kernel otherwise; secret memory areas are removed from the direct map and functions in the follow_page()/get_user_page() family will refuse to return a page that belongs to the secret memory area.
Once there will be a use case that will require exposing secretmem to the kernel it will be an opt-in request in the system call flags so that user would have to decide what data can be exposed to the kernel.
Removing of the pages from the direct map may cause its fragmentation on architectures that use large pages to map the physical memory which affects the system performance. However, the original Kconfig text for CONFIG_DIRECT_GBPAGES said that gigabyte pages in the direct map "... can improve the kernel's performance a tiny bit ..." (commit 00d1c5e05736 ("x86: add gbpages switches")) and the recent report [1] showed that "... although 1G mappings are a good default choice, there is no compelling evidence that it must be the only choice". Hence, it is sufficient to have secretmem disabled by default with the ability of a system administrator to enable it at boot time.
Pages in the secretmem regions are unevictable and unmovable to avoid accidental exposure of the sensitive data via swap or during page migration.
Since the secretmem mappings are locked in memory they cannot exceed RLIMIT_MEMLOCK. Since these mappings are already locked independently from mlock(), an attempt to mlock()/munlock() secretmem range would fail and mlockall()/munlockall() will ignore secretmem mappings.
However, unlike mlock()ed memory, secretmem currently behaves more like long-term GUP: secretmem mappings are unmovable mappings directly consumed by user space. With default limits, there is no excessive use of secretmem and it poses no real problem in combination with ZONE_MOVABLE/CMA, but in the future this should be addressed to allow balanced use of large amounts of secretmem along with ZONE_MOVABLE/CMA.
A page that was a part of the secret memory area is cleared when it is freed to ensure the data is not exposed to the next user of that page.
The following example demonstrates creation of a secret mapping (error handling is omitted):
fd = memfd_secret(0); ftruncate(fd, MAP_SIZE); ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
[1] https://lore.kernel.org/linux-mm/213b4567-46ce-f116-9cdf-bbd0c884eb3c@linux....
Signed-off-by: Mike Rapoport rppt@linux.ibm.com Acked-by: Hagen Paul Pfeifer hagen@jauu.net Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andy Lutomirski luto@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: Borislav Petkov bp@alien8.de Cc: Catalin Marinas catalin.marinas@arm.com Cc: Christopher Lameter cl@linux.com Cc: Dan Williams dan.j.williams@intel.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Elena Reshetova elena.reshetova@intel.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: James Bottomley jejb@linux.ibm.com Cc: "Kirill A. Shutemov" kirill@shutemov.name Cc: Matthew Wilcox willy@infradead.org Cc: Mark Rutland mark.rutland@arm.com Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Palmer Dabbelt palmerdabbelt@google.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Peter Zijlstra peterz@infradead.org Cc: Rick Edgecombe rick.p.edgecombe@intel.com Cc: Roman Gushchin guro@fb.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Tycho Andersen tycho@tycho.ws Cc: Will Deacon will@kernel.org --- include/linux/secretmem.h | 24 ++++ include/uapi/linux/magic.h | 1 + kernel/sys_ni.c | 2 + mm/Kconfig | 3 + mm/Makefile | 1 + mm/gup.c | 10 ++ mm/mlock.c | 3 +- mm/secretmem.c | 246 +++++++++++++++++++++++++++++++++++++ 8 files changed, 289 insertions(+), 1 deletion(-) create mode 100644 include/linux/secretmem.h create mode 100644 mm/secretmem.c
diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h new file mode 100644 index 000000000000..70e7db9f94fe --- /dev/null +++ b/include/linux/secretmem.h @@ -0,0 +1,24 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _LINUX_SECRETMEM_H +#define _LINUX_SECRETMEM_H + +#ifdef CONFIG_SECRETMEM + +bool vma_is_secretmem(struct vm_area_struct *vma); +bool page_is_secretmem(struct page *page); + +#else + +static inline bool vma_is_secretmem(struct vm_area_struct *vma) +{ + return false; +} + +static inline bool page_is_secretmem(struct page *page) +{ + return false; +} + +#endif /* CONFIG_SECRETMEM */ + +#endif /* _LINUX_SECRETMEM_H */ diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h index f3956fc11de6..35687dcb1a42 100644 --- a/include/uapi/linux/magic.h +++ b/include/uapi/linux/magic.h @@ -97,5 +97,6 @@ #define DEVMEM_MAGIC 0x454d444d /* "DMEM" */ #define Z3FOLD_MAGIC 0x33 #define PPC_CMM_MAGIC 0xc7571590 +#define SECRETMEM_MAGIC 0x5345434d /* "SECM" */
#endif /* __LINUX_MAGIC_H__ */ diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index 19aa806890d5..e9a2011ee4a2 100644 --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -352,6 +352,8 @@ COND_SYSCALL(pkey_mprotect); COND_SYSCALL(pkey_alloc); COND_SYSCALL(pkey_free);
+/* memfd_secret */ +COND_SYSCALL(memfd_secret);
/* * Architecture specific weak syscall entries. diff --git a/mm/Kconfig b/mm/Kconfig index 24c045b24b95..5f8243442f66 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -872,4 +872,7 @@ config MAPPING_DIRTY_HELPERS config KMAP_LOCAL bool
+config SECRETMEM + def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED + endmenu diff --git a/mm/Makefile b/mm/Makefile index 72227b24a616..b2a564eec27f 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -120,3 +120,4 @@ obj-$(CONFIG_MEMFD_CREATE) += memfd.o obj-$(CONFIG_MAPPING_DIRTY_HELPERS) += mapping_dirty_helpers.o obj-$(CONFIG_PTDUMP_CORE) += ptdump.o obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o +obj-$(CONFIG_SECRETMEM) += secretmem.o diff --git a/mm/gup.c b/mm/gup.c index e40579624f10..ecadc80934b2 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -10,6 +10,7 @@ #include <linux/rmap.h> #include <linux/swap.h> #include <linux/swapops.h> +#include <linux/secretmem.h>
#include <linux/sched/signal.h> #include <linux/rwsem.h> @@ -758,6 +759,9 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, struct follow_page_context ctx = { NULL }; struct page *page;
+ if (vma_is_secretmem(vma)) + return NULL; + page = follow_page_mask(vma, address, foll_flags, &ctx); if (ctx.pgmap) put_dev_pagemap(ctx.pgmap); @@ -891,6 +895,9 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) if ((gup_flags & FOLL_LONGTERM) && vma_is_fsdax(vma)) return -EOPNOTSUPP;
+ if (vma_is_secretmem(vma)) + return -EFAULT; + if (write) { if (!(vm_flags & VM_WRITE)) { if (!(gup_flags & FOLL_FORCE)) @@ -2030,6 +2037,9 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte);
+ if (page_is_secretmem(page)) + goto pte_unmap; + head = try_grab_compound_head(page, 1, flags); if (!head) goto pte_unmap; diff --git a/mm/mlock.c b/mm/mlock.c index f8f8cc32d03d..188711c72b67 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -23,6 +23,7 @@ #include <linux/hugetlb.h> #include <linux/memcontrol.h> #include <linux/mm_inline.h> +#include <linux/secretmem.h>
#include "internal.h"
@@ -503,7 +504,7 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) || is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) || - vma_is_dax(vma)) + vma_is_dax(vma) || vma_is_secretmem(vma)) /* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */ goto out;
diff --git a/mm/secretmem.c b/mm/secretmem.c new file mode 100644 index 000000000000..fa6738e860c2 --- /dev/null +++ b/mm/secretmem.c @@ -0,0 +1,246 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright IBM Corporation, 2021 + * + * Author: Mike Rapoport rppt@linux.ibm.com + */ + +#include <linux/mm.h> +#include <linux/fs.h> +#include <linux/swap.h> +#include <linux/mount.h> +#include <linux/memfd.h> +#include <linux/bitops.h> +#include <linux/printk.h> +#include <linux/pagemap.h> +#include <linux/syscalls.h> +#include <linux/pseudo_fs.h> +#include <linux/secretmem.h> +#include <linux/set_memory.h> +#include <linux/sched/signal.h> + +#include <uapi/linux/magic.h> + +#include <asm/tlbflush.h> + +#include "internal.h" + +#undef pr_fmt +#define pr_fmt(fmt) "secretmem: " fmt + +/* + * Define mode and flag masks to allow validation of the system call + * parameters. + */ +#define SECRETMEM_MODE_MASK (0x0) +#define SECRETMEM_FLAGS_MASK SECRETMEM_MODE_MASK + +static bool secretmem_enable __ro_after_init; +module_param_named(enable, secretmem_enable, bool, 0400); +MODULE_PARM_DESC(secretmem_enable, + "Enable secretmem and memfd_secret(2) system call"); + +static vm_fault_t secretmem_fault(struct vm_fault *vmf) +{ + struct address_space *mapping = vmf->vma->vm_file->f_mapping; + struct inode *inode = file_inode(vmf->vma->vm_file); + pgoff_t offset = vmf->pgoff; + gfp_t gfp = vmf->gfp_mask; + unsigned long addr; + struct page *page; + int err; + + if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) + return vmf_error(-EINVAL); + +retry: + page = find_lock_page(mapping, offset); + if (!page) { + page = alloc_page(gfp | __GFP_ZERO); + if (!page) + return VM_FAULT_OOM; + + err = set_direct_map_invalid_noflush(page, 1); + if (err) { + put_page(page); + return vmf_error(err); + } + + __SetPageUptodate(page); + err = add_to_page_cache_lru(page, mapping, offset, gfp); + if (unlikely(err)) { + put_page(page); + /* + * If a split of large page was required, it + * already happened when we marked the page invalid + * which guarantees that this call won't fail + */ + set_direct_map_default_noflush(page, 1); + if (err == -EEXIST) + goto retry; + + return vmf_error(err); + } + + addr = (unsigned long)page_address(page); + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); + } + + vmf->page = page; + return VM_FAULT_LOCKED; +} + +static const struct vm_operations_struct secretmem_vm_ops = { + .fault = secretmem_fault, +}; + +static int secretmem_mmap(struct file *file, struct vm_area_struct *vma) +{ + unsigned long len = vma->vm_end - vma->vm_start; + + if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0) + return -EINVAL; + + if (mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len)) + return -EAGAIN; + + vma->vm_flags |= VM_LOCKED | VM_DONTDUMP; + vma->vm_ops = &secretmem_vm_ops; + + return 0; +} + +bool vma_is_secretmem(struct vm_area_struct *vma) +{ + return vma->vm_ops == &secretmem_vm_ops; +} + +static const struct file_operations secretmem_fops = { + .mmap = secretmem_mmap, +}; + +static bool secretmem_isolate_page(struct page *page, isolate_mode_t mode) +{ + return false; +} + +static int secretmem_migratepage(struct address_space *mapping, + struct page *newpage, struct page *page, + enum migrate_mode mode) +{ + return -EBUSY; +} + +static void secretmem_freepage(struct page *page) +{ + set_direct_map_default_noflush(page, 1); + clear_highpage(page); +} + +static const struct address_space_operations secretmem_aops = { + .freepage = secretmem_freepage, + .migratepage = secretmem_migratepage, + .isolate_page = secretmem_isolate_page, +}; + +bool page_is_secretmem(struct page *page) +{ + struct address_space *mapping = page_mapping(page); + + if (!mapping) + return false; + + return mapping->a_ops == &secretmem_aops; +} + +static struct vfsmount *secretmem_mnt; + +static struct file *secretmem_file_create(unsigned long flags) +{ + struct file *file = ERR_PTR(-ENOMEM); + struct inode *inode; + + inode = alloc_anon_inode(secretmem_mnt->mnt_sb); + if (IS_ERR(inode)) + return ERR_CAST(inode); + + file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem", + O_RDWR, &secretmem_fops); + if (IS_ERR(file)) + goto err_free_inode; + + mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); + mapping_set_unevictable(inode->i_mapping); + + inode->i_mapping->a_ops = &secretmem_aops; + + /* pretend we are a normal file with zero size */ + inode->i_mode |= S_IFREG; + inode->i_size = 0; + + return file; + +err_free_inode: + iput(inode); + return file; +} + +SYSCALL_DEFINE1(memfd_secret, unsigned long, flags) +{ + struct file *file; + int fd, err; + + /* make sure local flags do not confict with global fcntl.h */ + BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC); + + if (!secretmem_enable) + return -ENOSYS; + + if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC)) + return -EINVAL; + + fd = get_unused_fd_flags(flags & O_CLOEXEC); + if (fd < 0) + return fd; + + file = secretmem_file_create(flags); + if (IS_ERR(file)) { + err = PTR_ERR(file); + goto err_put_fd; + } + + file->f_flags |= O_LARGEFILE; + + fd_install(fd, file); + return fd; + +err_put_fd: + put_unused_fd(fd); + return err; +} + +static int secretmem_init_fs_context(struct fs_context *fc) +{ + return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM; +} + +static struct file_system_type secretmem_fs = { + .name = "secretmem", + .init_fs_context = secretmem_init_fs_context, + .kill_sb = kill_anon_super, +}; + +static int secretmem_init(void) +{ + int ret = 0; + + if (!secretmem_enable) + return ret; + + secretmem_mnt = kern_mount(&secretmem_fs); + if (IS_ERR(secretmem_mnt)) + ret = PTR_ERR(secretmem_mnt); + + return ret; +} +fs_initcall(secretmem_init);
From: Mike Rapoport rppt@linux.ibm.com
It is unsafe to allow saving of secretmem areas to the hibernation snapshot as they would be visible after the resume and this essentially will defeat the purpose of secret memory mappings.
Prevent hibernation whenever there are active secret memory users.
Signed-off-by: Mike Rapoport rppt@linux.ibm.com Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andy Lutomirski luto@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: Borislav Petkov bp@alien8.de Cc: Catalin Marinas catalin.marinas@arm.com Cc: Christopher Lameter cl@linux.com Cc: Dan Williams dan.j.williams@intel.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: David Hildenbrand david@redhat.com Cc: Elena Reshetova elena.reshetova@intel.com Cc: Hagen Paul Pfeifer hagen@jauu.net Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: James Bottomley jejb@linux.ibm.com Cc: "Kirill A. Shutemov" kirill@shutemov.name Cc: Mark Rutland mark.rutland@arm.com Cc: Matthew Wilcox willy@infradead.org Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Palmer Dabbelt palmerdabbelt@google.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Peter Zijlstra peterz@infradead.org Cc: Rick Edgecombe rick.p.edgecombe@intel.com Cc: Roman Gushchin guro@fb.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Tycho Andersen tycho@tycho.ws Cc: Will Deacon will@kernel.org --- include/linux/secretmem.h | 6 ++++++ kernel/power/hibernate.c | 5 ++++- mm/secretmem.c | 15 +++++++++++++++ 3 files changed, 25 insertions(+), 1 deletion(-)
diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h index 70e7db9f94fe..907a6734059c 100644 --- a/include/linux/secretmem.h +++ b/include/linux/secretmem.h @@ -6,6 +6,7 @@
bool vma_is_secretmem(struct vm_area_struct *vma); bool page_is_secretmem(struct page *page); +bool secretmem_active(void);
#else
@@ -19,6 +20,11 @@ static inline bool page_is_secretmem(struct page *page) return false; }
+static inline bool secretmem_active(void) +{ + return false; +} + #endif /* CONFIG_SECRETMEM */
#endif /* _LINUX_SECRETMEM_H */ diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c index da0b41914177..559acef3fddb 100644 --- a/kernel/power/hibernate.c +++ b/kernel/power/hibernate.c @@ -31,6 +31,7 @@ #include <linux/genhd.h> #include <linux/ktime.h> #include <linux/security.h> +#include <linux/secretmem.h> #include <trace/events/power.h>
#include "power.h" @@ -81,7 +82,9 @@ void hibernate_release(void)
bool hibernation_available(void) { - return nohibernate == 0 && !security_locked_down(LOCKDOWN_HIBERNATION); + return nohibernate == 0 && + !security_locked_down(LOCKDOWN_HIBERNATION) && + !secretmem_active(); }
/** diff --git a/mm/secretmem.c b/mm/secretmem.c index fa6738e860c2..f2ae3f32a193 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -40,6 +40,13 @@ module_param_named(enable, secretmem_enable, bool, 0400); MODULE_PARM_DESC(secretmem_enable, "Enable secretmem and memfd_secret(2) system call");
+static atomic_t secretmem_users; + +bool secretmem_active(void) +{ + return !!atomic_read(&secretmem_users); +} + static vm_fault_t secretmem_fault(struct vm_fault *vmf) { struct address_space *mapping = vmf->vma->vm_file->f_mapping; @@ -94,6 +101,12 @@ static const struct vm_operations_struct secretmem_vm_ops = { .fault = secretmem_fault, };
+static int secretmem_release(struct inode *inode, struct file *file) +{ + atomic_dec(&secretmem_users); + return 0; +} + static int secretmem_mmap(struct file *file, struct vm_area_struct *vma) { unsigned long len = vma->vm_end - vma->vm_start; @@ -116,6 +129,7 @@ bool vma_is_secretmem(struct vm_area_struct *vma) }
static const struct file_operations secretmem_fops = { + .release = secretmem_release, .mmap = secretmem_mmap, };
@@ -212,6 +226,7 @@ SYSCALL_DEFINE1(memfd_secret, unsigned long, flags) file->f_flags |= O_LARGEFILE;
fd_install(fd, file); + atomic_inc(&secretmem_users); return fd;
err_put_fd:
From: Mike Rapoport rppt@linux.ibm.com
Wire up memfd_secret system call on architectures that define ARCH_HAS_SET_DIRECT_MAP, namely arm64, risc-v and x86.
Signed-off-by: Mike Rapoport rppt@linux.ibm.com Acked-by: Palmer Dabbelt palmerdabbelt@google.com Acked-by: Arnd Bergmann arnd@arndb.de Acked-by: Catalin Marinas catalin.marinas@arm.com Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Christopher Lameter cl@linux.com Cc: Dan Williams dan.j.williams@intel.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: David Hildenbrand david@redhat.com Cc: Elena Reshetova elena.reshetova@intel.com Cc: Hagen Paul Pfeifer hagen@jauu.net Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: James Bottomley jejb@linux.ibm.com Cc: "Kirill A. Shutemov" kirill@shutemov.name Cc: Mark Rutland mark.rutland@arm.com Cc: Matthew Wilcox willy@infradead.org Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Peter Zijlstra peterz@infradead.org Cc: Rick Edgecombe rick.p.edgecombe@intel.com Cc: Roman Gushchin guro@fb.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Tycho Andersen tycho@tycho.ws Cc: Will Deacon will@kernel.org --- arch/arm64/include/uapi/asm/unistd.h | 1 + arch/riscv/include/asm/unistd.h | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + include/linux/syscalls.h | 1 + include/uapi/asm-generic/unistd.h | 6 +++++- scripts/checksyscalls.sh | 4 ++++ 7 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/uapi/asm/unistd.h b/arch/arm64/include/uapi/asm/unistd.h index f83a70e07df8..ce2ee8f1e361 100644 --- a/arch/arm64/include/uapi/asm/unistd.h +++ b/arch/arm64/include/uapi/asm/unistd.h @@ -20,5 +20,6 @@ #define __ARCH_WANT_SET_GET_RLIMIT #define __ARCH_WANT_TIME32_SYSCALLS #define __ARCH_WANT_SYS_CLONE3 +#define __ARCH_WANT_MEMFD_SECRET
#include <asm-generic/unistd.h> diff --git a/arch/riscv/include/asm/unistd.h b/arch/riscv/include/asm/unistd.h index 977ee6181dab..6c316093a1e5 100644 --- a/arch/riscv/include/asm/unistd.h +++ b/arch/riscv/include/asm/unistd.h @@ -9,6 +9,7 @@ */
#define __ARCH_WANT_SYS_CLONE +#define __ARCH_WANT_MEMFD_SECRET
#include <uapi/asm/unistd.h>
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index a1c9f496fca6..34f04076a140 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -447,3 +447,4 @@ 440 i386 process_madvise sys_process_madvise 441 i386 epoll_pwait2 sys_epoll_pwait2 compat_sys_epoll_pwait2 442 i386 mount_setattr sys_mount_setattr +443 i386 memfd_secret sys_memfd_secret diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index 7bf01cbe582f..bd3783edf27f 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -364,6 +364,7 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +443 common memfd_secret sys_memfd_secret
# # Due to a historical design error, certain syscalls are numbered differently diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 2839dc9a7c01..4b87a2b3f442 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -1041,6 +1041,7 @@ asmlinkage long sys_pidfd_send_signal(int pidfd, int sig, siginfo_t __user *info, unsigned int flags); asmlinkage long sys_pidfd_getfd(int pidfd, int fd, unsigned int flags); +asmlinkage long sys_memfd_secret(unsigned long flags);
/* * Architecture-specific system calls diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index ce58cff99b66..7ac0732dbaa4 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -863,9 +863,13 @@ __SYSCALL(__NR_process_madvise, sys_process_madvise) __SC_COMP(__NR_epoll_pwait2, sys_epoll_pwait2, compat_sys_epoll_pwait2) #define __NR_mount_setattr 442 __SYSCALL(__NR_mount_setattr, sys_mount_setattr) +#ifdef __ARCH_WANT_MEMFD_SECRET +#define __NR_memfd_secret 443 +__SYSCALL(__NR_memfd_secret, sys_memfd_secret) +#endif
#undef __NR_syscalls -#define __NR_syscalls 443 +#define __NR_syscalls 444
/* * 32 bit systems traditionally used different diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh index a18b47695f55..b7609958ee36 100755 --- a/scripts/checksyscalls.sh +++ b/scripts/checksyscalls.sh @@ -40,6 +40,10 @@ cat << EOF #define __IGNORE_setrlimit /* setrlimit */ #endif
+#ifndef __ARCH_WANT_MEMFD_SECRET +#define __IGNORE_memfd_secret +#endif + /* Missing flags argument */ #define __IGNORE_renameat /* renameat2 */
From: Mike Rapoport rppt@linux.ibm.com
The test verifies that file descriptor created with memfd_secret does not allow read/write operations, that secret memory mappings respect RLIMIT_MEMLOCK and that remote accesses with process_vm_read() and ptrace() to the secret memory fail.
Signed-off-by: Mike Rapoport rppt@linux.ibm.com Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andy Lutomirski luto@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: Borislav Petkov bp@alien8.de Cc: Catalin Marinas catalin.marinas@arm.com Cc: Christopher Lameter cl@linux.com Cc: Dan Williams dan.j.williams@intel.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: David Hildenbrand david@redhat.com Cc: Elena Reshetova elena.reshetova@intel.com Cc: Hagen Paul Pfeifer hagen@jauu.net Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: James Bottomley jejb@linux.ibm.com Cc: "Kirill A. Shutemov" kirill@shutemov.name Cc: Mark Rutland mark.rutland@arm.com Cc: Matthew Wilcox willy@infradead.org Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Palmer Dabbelt palmerdabbelt@google.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Peter Zijlstra peterz@infradead.org Cc: Rick Edgecombe rick.p.edgecombe@intel.com Cc: Roman Gushchin guro@fb.com Cc: Shakeel Butt shakeelb@google.com Cc: Shuah Khan shuah@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Tycho Andersen tycho@tycho.ws Cc: Will Deacon will@kernel.org --- tools/testing/selftests/vm/.gitignore | 1 + tools/testing/selftests/vm/Makefile | 3 +- tools/testing/selftests/vm/memfd_secret.c | 296 ++++++++++++++++++++++ tools/testing/selftests/vm/run_vmtests.sh | 17 ++ 4 files changed, 316 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/vm/memfd_secret.c
diff --git a/tools/testing/selftests/vm/.gitignore b/tools/testing/selftests/vm/.gitignore index 9a35c3f6a557..c8deddc81e7a 100644 --- a/tools/testing/selftests/vm/.gitignore +++ b/tools/testing/selftests/vm/.gitignore @@ -21,4 +21,5 @@ va_128TBswitch map_fixed_noreplace write_to_hugetlbfs hmm-tests +memfd_secret local_config.* diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile index d42115e4284d..0200fb61646c 100644 --- a/tools/testing/selftests/vm/Makefile +++ b/tools/testing/selftests/vm/Makefile @@ -34,6 +34,7 @@ TEST_GEN_FILES += khugepaged TEST_GEN_FILES += map_fixed_noreplace TEST_GEN_FILES += map_hugetlb TEST_GEN_FILES += map_populate +TEST_GEN_FILES += memfd_secret TEST_GEN_FILES += mlock-random-test TEST_GEN_FILES += mlock2-tests TEST_GEN_FILES += mremap_dontunmap @@ -133,7 +134,7 @@ warn_32bit_failure: endif endif
-$(OUTPUT)/mlock-random-test: LDLIBS += -lcap +$(OUTPUT)/mlock-random-test $(OUTPUT)/memfd_secret: LDLIBS += -lcap
$(OUTPUT)/gup_test: ../../../../mm/gup_test.h
diff --git a/tools/testing/selftests/vm/memfd_secret.c b/tools/testing/selftests/vm/memfd_secret.c new file mode 100644 index 000000000000..c878c2b841fc --- /dev/null +++ b/tools/testing/selftests/vm/memfd_secret.c @@ -0,0 +1,296 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright IBM Corporation, 2020 + * + * Author: Mike Rapoport rppt@linux.ibm.com + */ + +#define _GNU_SOURCE +#include <sys/uio.h> +#include <sys/mman.h> +#include <sys/wait.h> +#include <sys/types.h> +#include <sys/ptrace.h> +#include <sys/syscall.h> +#include <sys/resource.h> +#include <sys/capability.h> + +#include <stdlib.h> +#include <string.h> +#include <unistd.h> +#include <errno.h> +#include <stdio.h> + +#include "../kselftest.h" + +#define fail(fmt, ...) ksft_test_result_fail(fmt, ##__VA_ARGS__) +#define pass(fmt, ...) ksft_test_result_pass(fmt, ##__VA_ARGS__) +#define skip(fmt, ...) ksft_test_result_skip(fmt, ##__VA_ARGS__) + +#ifdef __NR_memfd_secret + +#define PATTERN 0x55 + +static const int prot = PROT_READ | PROT_WRITE; +static const int mode = MAP_SHARED; + +static unsigned long page_size; +static unsigned long mlock_limit_cur; +static unsigned long mlock_limit_max; + +static int memfd_secret(unsigned long flags) +{ + return syscall(__NR_memfd_secret, flags); +} + +static void test_file_apis(int fd) +{ + char buf[64]; + + if ((read(fd, buf, sizeof(buf)) >= 0) || + (write(fd, buf, sizeof(buf)) >= 0) || + (pread(fd, buf, sizeof(buf), 0) >= 0) || + (pwrite(fd, buf, sizeof(buf), 0) >= 0)) + fail("unexpected file IO\n"); + else + pass("file IO is blocked as expected\n"); +} + +static void test_mlock_limit(int fd) +{ + size_t len; + char *mem; + + len = mlock_limit_cur; + mem = mmap(NULL, len, prot, mode, fd, 0); + if (mem == MAP_FAILED) { + fail("unable to mmap secret memory\n"); + return; + } + munmap(mem, len); + + len = mlock_limit_max * 2; + mem = mmap(NULL, len, prot, mode, fd, 0); + if (mem != MAP_FAILED) { + fail("unexpected mlock limit violation\n"); + munmap(mem, len); + return; + } + + pass("mlock limit is respected\n"); +} + +static void try_process_vm_read(int fd, int pipefd[2]) +{ + struct iovec liov, riov; + char buf[64]; + char *mem; + + if (read(pipefd[0], &mem, sizeof(mem)) < 0) { + fail("pipe write: %s\n", strerror(errno)); + exit(KSFT_FAIL); + } + + liov.iov_len = riov.iov_len = sizeof(buf); + liov.iov_base = buf; + riov.iov_base = mem; + + if (process_vm_readv(getppid(), &liov, 1, &riov, 1, 0) < 0) { + if (errno == ENOSYS) + exit(KSFT_SKIP); + exit(KSFT_PASS); + } + + exit(KSFT_FAIL); +} + +static void try_ptrace(int fd, int pipefd[2]) +{ + pid_t ppid = getppid(); + int status; + char *mem; + long ret; + + if (read(pipefd[0], &mem, sizeof(mem)) < 0) { + perror("pipe write"); + exit(KSFT_FAIL); + } + + ret = ptrace(PTRACE_ATTACH, ppid, 0, 0); + if (ret) { + perror("ptrace_attach"); + exit(KSFT_FAIL); + } + + ret = waitpid(ppid, &status, WUNTRACED); + if ((ret != ppid) || !(WIFSTOPPED(status))) { + fprintf(stderr, "weird waitppid result %ld stat %x\n", + ret, status); + exit(KSFT_FAIL); + } + + if (ptrace(PTRACE_PEEKDATA, ppid, mem, 0)) + exit(KSFT_PASS); + + exit(KSFT_FAIL); +} + +static void check_child_status(pid_t pid, const char *name) +{ + int status; + + waitpid(pid, &status, 0); + + if (WIFEXITED(status) && WEXITSTATUS(status) == KSFT_SKIP) { + skip("%s is not supported\n", name); + return; + } + + if ((WIFEXITED(status) && WEXITSTATUS(status) == KSFT_PASS) || + WIFSIGNALED(status)) { + pass("%s is blocked as expected\n", name); + return; + } + + fail("%s: unexpected memory access\n", name); +} + +static void test_remote_access(int fd, const char *name, + void (*func)(int fd, int pipefd[2])) +{ + int pipefd[2]; + pid_t pid; + char *mem; + + if (pipe(pipefd)) { + fail("pipe failed: %s\n", strerror(errno)); + return; + } + + pid = fork(); + if (pid < 0) { + fail("fork failed: %s\n", strerror(errno)); + return; + } + + if (pid == 0) { + func(fd, pipefd); + return; + } + + mem = mmap(NULL, page_size, prot, mode, fd, 0); + if (mem == MAP_FAILED) { + fail("Unable to mmap secret memory\n"); + return; + } + + ftruncate(fd, page_size); + memset(mem, PATTERN, page_size); + + if (write(pipefd[1], &mem, sizeof(mem)) < 0) { + fail("pipe write: %s\n", strerror(errno)); + return; + } + + check_child_status(pid, name); +} + +static void test_process_vm_read(int fd) +{ + test_remote_access(fd, "process_vm_read", try_process_vm_read); +} + +static void test_ptrace(int fd) +{ + test_remote_access(fd, "ptrace", try_ptrace); +} + +static int set_cap_limits(rlim_t max) +{ + struct rlimit new; + cap_t cap = cap_init(); + + new.rlim_cur = max; + new.rlim_max = max; + if (setrlimit(RLIMIT_MEMLOCK, &new)) { + perror("setrlimit() returns error"); + return -1; + } + + /* drop capabilities including CAP_IPC_LOCK */ + if (cap_set_proc(cap)) { + perror("cap_set_proc() returns error"); + return -2; + } + + return 0; +} + +static void prepare(void) +{ + struct rlimit rlim; + + page_size = sysconf(_SC_PAGE_SIZE); + if (!page_size) + ksft_exit_fail_msg("Failed to get page size %s\n", + strerror(errno)); + + if (getrlimit(RLIMIT_MEMLOCK, &rlim)) + ksft_exit_fail_msg("Unable to detect mlock limit: %s\n", + strerror(errno)); + + mlock_limit_cur = rlim.rlim_cur; + mlock_limit_max = rlim.rlim_max; + + printf("page_size: %ld, mlock.soft: %ld, mlock.hard: %ld\n", + page_size, mlock_limit_cur, mlock_limit_max); + + if (page_size > mlock_limit_cur) + mlock_limit_cur = page_size; + if (page_size > mlock_limit_max) + mlock_limit_max = page_size; + + if (set_cap_limits(mlock_limit_max)) + ksft_exit_fail_msg("Unable to set mlock limit: %s\n", + strerror(errno)); +} + +#define NUM_TESTS 4 + +int main(int argc, char *argv[]) +{ + int fd; + + prepare(); + + ksft_print_header(); + ksft_set_plan(NUM_TESTS); + + fd = memfd_secret(0); + if (fd < 0) { + if (errno == ENOSYS) + ksft_exit_skip("memfd_secret is not supported\n"); + else + ksft_exit_fail_msg("memfd_secret failed: %s\n", + strerror(errno)); + } + + test_mlock_limit(fd); + test_file_apis(fd); + test_process_vm_read(fd); + test_ptrace(fd); + + close(fd); + + ksft_exit(!ksft_get_fail_cnt()); +} + +#else /* __NR_memfd_secret */ + +int main(int argc, char *argv[]) +{ + printf("skip: skipping memfd_secret test (missing __NR_memfd_secret)\n"); + return KSFT_SKIP; +} + +#endif /* __NR_memfd_secret */ diff --git a/tools/testing/selftests/vm/run_vmtests.sh b/tools/testing/selftests/vm/run_vmtests.sh index e953f3cd9664..95a67382f132 100755 --- a/tools/testing/selftests/vm/run_vmtests.sh +++ b/tools/testing/selftests/vm/run_vmtests.sh @@ -346,4 +346,21 @@ else exitcode=1 fi
+echo "running memfd_secret test" +echo "------------------------------------" +./memfd_secret +ret_val=$? + +if [ $ret_val -eq 0 ]; then + echo "[PASS]" +elif [ $ret_val -eq $ksft_skip ]; then + echo "[SKIP]" + exitcode=$ksft_skip +else + echo "[FAIL]" + exitcode=1 +fi + +exit $exitcode + exit $exitcode
On Wed, 3 Mar 2021 18:22:00 +0200 Mike Rapoport rppt@kernel.org wrote:
This is an implementation of "secret" mappings backed by a file descriptor.
The file descriptor backing secret memory mappings is created using a dedicated memfd_secret system call The desired protection mode for the memory is configured using flags parameter of the system call. The mmap() of the file descriptor created with memfd_secret() will create a "secret" memory mapping. The pages in that mapping will be marked as not present in the direct map and will be present only in the page table of the owning mm.
Although normally Linux userspace mappings are protected from other users, such secret mappings are useful for environments where a hostile tenant is trying to trick the kernel into giving them access to other tenants mappings.
I continue to struggle with this and I don't recall seeing much enthusiasm from others. Perhaps we're all missing the value point and some additional selling is needed.
Am I correct in understanding that the overall direction here is to protect keys (and perhaps other things) from kernel bugs? That if the kernel was bug-free then there would be no need for this feature? If so, that's a bit sad. But realistic I guess.
Is this intended to protect keys/etc after the attacker has gained the ability to run arbitrary kernel-mode code? If so, that seems optimistic, doesn't it?
I think that a very complete description of the threats which this feature addresses would be helpful.
On Wed, 2021-05-05 at 12:08 -0700, Andrew Morton wrote:
On Wed, 3 Mar 2021 18:22:00 +0200 Mike Rapoport rppt@kernel.org wrote:
This is an implementation of "secret" mappings backed by a file descriptor.
The file descriptor backing secret memory mappings is created using a dedicated memfd_secret system call The desired protection mode for the memory is configured using flags parameter of the system call. The mmap() of the file descriptor created with memfd_secret() will create a "secret" memory mapping. The pages in that mapping will be marked as not present in the direct map and will be present only in the page table of the owning mm.
Although normally Linux userspace mappings are protected from other users, such secret mappings are useful for environments where a hostile tenant is trying to trick the kernel into giving them access to other tenants mappings.
I continue to struggle with this and I don't recall seeing much enthusiasm from others. Perhaps we're all missing the value point and some additional selling is needed.
Am I correct in understanding that the overall direction here is to protect keys (and perhaps other things) from kernel bugs? That if the kernel was bug-free then there would be no need for this feature? If so, that's a bit sad. But realistic I guess.
Secret memory really serves several purposes. The "increase the level of difficulty of secret exfiltration" you describe. And, as you say, if the kernel were bug free this wouldn't be necessary.
But also:
1. Memory safety for use space code. Once the secret memory is allocated, the user can't accidentally pass it into the kernel to be transmitted somewhere. 2. It also serves as a basis for context protection of virtual machines, but other groups are working on this aspect, and it is broadly similar to the secret exfiltration from the kernel problem.
Is this intended to protect keys/etc after the attacker has gained the ability to run arbitrary kernel-mode code? If so, that seems optimistic, doesn't it?
Not exactly: there are many types of kernel attack, but mostly the attacker either manages to effect a privilege escalation to root or gets the ability to run a ROP gadget. The object of this code is to be completely secure against root trying to extract the secret (some what similar to the lockdown idea), thus defeating privilege escalation and to provide "sufficient" protection against ROP gadgets.
The ROP gadget thing needs more explanation: the usual defeatist approach is to say that once the attacker gains the stack, they can do anything because they can find enough ROP gadgets to be turing complete. However, in the real world, given the kernel stack size limit and address space layout randomization making finding gadgets really hard, usually the attacker gets one or at most two gadgets to string together. Not having any in-kernel primitive for accessing secret memory means the one gadget ROP attack can't work. Since the only way to access secret memory is to reconstruct the missing mapping entry, the attacker has to recover the physical page and insert a PTE pointing to it in the kernel and then retrieve the contents. That takes at least three gadgets which is a level of difficulty beyond most standard attacks.
I think that a very complete description of the threats which this feature addresses would be helpful.
It's designed to protect against three different threats:
1. Detection of user secret memory mismanagement 2. significant protection against privilege escalation 3. enhanced protection (in conjunction with all the other in-kernel attack prevention systems) against ROP attacks.
Do you want us to add this to one of the patch descriptions?
James
On 06.05.21 17:26, James Bottomley wrote:
On Wed, 2021-05-05 at 12:08 -0700, Andrew Morton wrote:
On Wed, 3 Mar 2021 18:22:00 +0200 Mike Rapoport rppt@kernel.org wrote:
This is an implementation of "secret" mappings backed by a file descriptor.
The file descriptor backing secret memory mappings is created using a dedicated memfd_secret system call The desired protection mode for the memory is configured using flags parameter of the system call. The mmap() of the file descriptor created with memfd_secret() will create a "secret" memory mapping. The pages in that mapping will be marked as not present in the direct map and will be present only in the page table of the owning mm.
Although normally Linux userspace mappings are protected from other users, such secret mappings are useful for environments where a hostile tenant is trying to trick the kernel into giving them access to other tenants mappings.
I continue to struggle with this and I don't recall seeing much enthusiasm from others. Perhaps we're all missing the value point and some additional selling is needed.
Am I correct in understanding that the overall direction here is to protect keys (and perhaps other things) from kernel bugs? That if the kernel was bug-free then there would be no need for this feature? If so, that's a bit sad. But realistic I guess.
Secret memory really serves several purposes. The "increase the level of difficulty of secret exfiltration" you describe. And, as you say, if the kernel were bug free this wouldn't be necessary.
But also:
1. Memory safety for use space code. Once the secret memory is allocated, the user can't accidentally pass it into the kernel to be transmitted somewhere.
That's an interesting point I didn't realize so far.
2. It also serves as a basis for context protection of virtual machines, but other groups are working on this aspect, and it is broadly similar to the secret exfiltration from the kernel problem.
I was wondering if this also helps against CPU microcode issues like spectre and friends.
Is this intended to protect keys/etc after the attacker has gained the ability to run arbitrary kernel-mode code? If so, that seems optimistic, doesn't it?
Not exactly: there are many types of kernel attack, but mostly the attacker either manages to effect a privilege escalation to root or gets the ability to run a ROP gadget. The object of this code is to be completely secure against root trying to extract the secret (some what similar to the lockdown idea), thus defeating privilege escalation and to provide "sufficient" protection against ROP gadget.
What stops "root" from mapping /dev/mem and reading that memory?
IOW, would we want to enforce "CONFIG_STRICT_DEVMEM" with CONFIG_SECRETMEM?
Also, there is a way to still read that memory when root by
1. Having kdump active (which would often be the case, but maybe not to dump user pages ) 2. Triggering a kernel crash (easy via proc as root) 3. Waiting for the reboot after kump() created the dump and then reading the content from disk.
Or, as an attacker, load a custom kexec() kernel and read memory from the new environment. Of course, the latter two are advanced mechanisms, but they are possible when root. We might be able to mitigate, for example, by zeroing out secretmem pages before booting into the kexec kernel, if we care :)
On Thu, 2021-05-06 at 18:45 +0200, David Hildenbrand wrote:
On 06.05.21 17:26, James Bottomley wrote:
On Wed, 2021-05-05 at 12:08 -0700, Andrew Morton wrote:
On Wed, 3 Mar 2021 18:22:00 +0200 Mike Rapoport <rppt@kernel.org
wrote:
This is an implementation of "secret" mappings backed by a file descriptor.
The file descriptor backing secret memory mappings is created using a dedicated memfd_secret system call The desired protection mode for the memory is configured using flags parameter of the system call. The mmap() of the file descriptor created with memfd_secret() will create a "secret" memory mapping. The pages in that mapping will be marked as not present in the direct map and will be present only in the page table of the owning mm.
Although normally Linux userspace mappings are protected from other users, such secret mappings are useful for environments where a hostile tenant is trying to trick the kernel into giving them access to other tenants mappings.
I continue to struggle with this and I don't recall seeing much enthusiasm from others. Perhaps we're all missing the value point and some additional selling is needed.
Am I correct in understanding that the overall direction here is to protect keys (and perhaps other things) from kernel bugs? That if the kernel was bug-free then there would be no need for this feature? If so, that's a bit sad. But realistic I guess.
Secret memory really serves several purposes. The "increase the level of difficulty of secret exfiltration" you describe. And, as you say, if the kernel were bug free this wouldn't be necessary.
But also:
1. Memory safety for use space code. Once the secret memory is allocated, the user can't accidentally pass it into thekernel to be transmitted somewhere.
That's an interesting point I didn't realize so far.
2. It also serves as a basis for context protection of virtual machines, but other groups are working on this aspect, andit is broadly similar to the secret exfiltration from the kernel problem.
I was wondering if this also helps against CPU microcode issues like spectre and friends.
It can for VMs, but not really for the user space secret memory use cases ... the in-kernel mitigations already present are much more effective.
Is this intended to protect keys/etc after the attacker has gained the ability to run arbitrary kernel-mode code? If so, that seems optimistic, doesn't it?
Not exactly: there are many types of kernel attack, but mostly the attacker either manages to effect a privilege escalation to root or gets the ability to run a ROP gadget. The object of this code is to be completely secure against root trying to extract the secret (some what similar to the lockdown idea), thus defeating privilege escalation and to provide "sufficient" protection against ROP gadget.
What stops "root" from mapping /dev/mem and reading that memory?
/dev/mem uses the direct map for the copy at least for read/write, so it gets a fault in the same way root trying to use ptrace does. I think we've protected mmap, but Mike would know that better than I.
IOW, would we want to enforce "CONFIG_STRICT_DEVMEM" with CONFIG_SECRETMEM?
Unless there's a corner case I haven't thought of, I don't think it adds much. However, doing a full lockdown on a public system where users want to use secret memory is best practice I think (except I think you want it to be the full secure boot lockdown to close all the root holes).
Also, there is a way to still read that memory when root by
- Having kdump active (which would often be the case, but maybe not
to dump user pages ) 2. Triggering a kernel crash (easy via proc as root) 3. Waiting for the reboot after kump() created the dump and then reading the content from disk.
Anything that can leave physical memory intact but boot to a kernel where the missing direct map entry is restored could theoretically extract the secret. However, it's not exactly going to be a stealthy extraction ...
Or, as an attacker, load a custom kexec() kernel and read memory from the new environment. Of course, the latter two are advanced mechanisms, but they are possible when root. We might be able to mitigate, for example, by zeroing out secretmem pages before booting into the kexec kernel, if we care :)
I think we could handle it by marking the region, yes, and a zero on shutdown might be useful ... it would prevent all warm reboot type attacks.
James
Is this intended to protect keys/etc after the attacker has gained the ability to run arbitrary kernel-mode code? If so, that seems optimistic, doesn't it?
Not exactly: there are many types of kernel attack, but mostly the attacker either manages to effect a privilege escalation to root or gets the ability to run a ROP gadget. The object of this code is to be completely secure against root trying to extract the secret (some what similar to the lockdown idea), thus defeating privilege escalation and to provide "sufficient" protection against ROP gadget.
What stops "root" from mapping /dev/mem and reading that memory?
/dev/mem uses the direct map for the copy at least for read/write, so it gets a fault in the same way root trying to use ptrace does. I think we've protected mmap, but Mike would know that better than I.
I'm more concerned about the mmap case -> remap_pfn_range(). Anybody going via the VMA shouldn't see the struct page, at least when vma_normal_page() is properly used; so you cannot detect secretmem memory mapped via /dev/mem reliably. At least that's my theory :)
[...]
Also, there is a way to still read that memory when root by
- Having kdump active (which would often be the case, but maybe not
to dump user pages ) 2. Triggering a kernel crash (easy via proc as root) 3. Waiting for the reboot after kump() created the dump and then reading the content from disk.
Anything that can leave physical memory intact but boot to a kernel where the missing direct map entry is restored could theoretically extract the secret. However, it's not exactly going to be a stealthy extraction ...
Or, as an attacker, load a custom kexec() kernel and read memory from the new environment. Of course, the latter two are advanced mechanisms, but they are possible when root. We might be able to mitigate, for example, by zeroing out secretmem pages before booting into the kexec kernel, if we care :)
I think we could handle it by marking the region, yes, and a zero on shutdown might be useful ... it would prevent all warm reboot type attacks.
Right. But I guess when you're actually root, you can just write a kernel module to extract the information you need (unless we have signed modules, so it could be harder/impossible).
Στις 2021-05-06 20:05, James Bottomley έγραψε:
On Thu, 2021-05-06 at 18:45 +0200, David Hildenbrand wrote:
Also, there is a way to still read that memory when root by
- Having kdump active (which would often be the case, but maybe not
to dump user pages ) 2. Triggering a kernel crash (easy via proc as root) 3. Waiting for the reboot after kump() created the dump and then reading the content from disk.
Anything that can leave physical memory intact but boot to a kernel where the missing direct map entry is restored could theoretically extract the secret. However, it's not exactly going to be a stealthy extraction ...
Or, as an attacker, load a custom kexec() kernel and read memory from the new environment. Of course, the latter two are advanced mechanisms, but they are possible when root. We might be able to mitigate, for example, by zeroing out secretmem pages before booting into the kexec kernel, if we care :)
I think we could handle it by marking the region, yes, and a zero on shutdown might be useful ... it would prevent all warm reboot type attacks.
I had similar concerns about recovering secrets with kdump, and considered cleaning up keyrings before jumping to the new kernel. The problem is we can't provide guarantees in that case, once the kernel has crashed and we are on our way to run crashkernel, we can't be sure we can reliably zero-out anything, the more code we add to that path the more risky it gets. However during reboot/normal kexec() we should do some cleanup, it makes sense and secretmem can indeed be useful in that case. Regarding loading custom kexec() kernels, we mitigate this with the kexec file-based API where we can verify the signature of the loaded kimage (assuming the system runs a kernel provided by a trusted 3rd party and we 've maintained a chain of trust since booting).
On 07.05.21 01:16, Nick Kossifidis wrote:
Στις 2021-05-06 20:05, James Bottomley έγραψε:
On Thu, 2021-05-06 at 18:45 +0200, David Hildenbrand wrote:
Also, there is a way to still read that memory when root by
- Having kdump active (which would often be the case, but maybe not
to dump user pages ) 2. Triggering a kernel crash (easy via proc as root) 3. Waiting for the reboot after kump() created the dump and then reading the content from disk.
Anything that can leave physical memory intact but boot to a kernel where the missing direct map entry is restored could theoretically extract the secret. However, it's not exactly going to be a stealthy extraction ...
Or, as an attacker, load a custom kexec() kernel and read memory from the new environment. Of course, the latter two are advanced mechanisms, but they are possible when root. We might be able to mitigate, for example, by zeroing out secretmem pages before booting into the kexec kernel, if we care :)
I think we could handle it by marking the region, yes, and a zero on shutdown might be useful ... it would prevent all warm reboot type attacks.
I had similar concerns about recovering secrets with kdump, and considered cleaning up keyrings before jumping to the new kernel. The problem is we can't provide guarantees in that case, once the kernel has crashed and we are on our way to run crashkernel, we can't be sure we can reliably zero-out anything, the more code we add to that path the
Well, I think it depends. Assume we do the following
1) Zero out any secretmem pages when handing them back to the buddy. (alternative: init_on_free=1) -- if not already done, I didn't check the code.
2) On kdump(), zero out all allocated secretmem. It'd be easier if we'd just allocated from a fixed physical memory area; otherwise we have to walk process page tables or use a PFN walker. And zeroing out secretmem pages without a direct mapping is a different challenge.
Now, during 2) it can happen that
a) We crash in our clearing code (e.g., something is seriously messed up) and fail to start the kdump kernel. That's actually good, instead of leaking data we fail hard.
b) We don't find all secretmem pages, for example, because process page tables are messed up or something messed up our memmap (if we'd use that to identify secretmem pages via a PFN walker somehow)
But for the simple cases (e.g., malicious root tries to crash the kernel via /proc/sysrq-trigger) both a) and b) wouldn't apply.
Obviously, if an admin would want to mitigate right now, he would want to disable kdump completely, meaning any attempt to load a crashkernel would fail and cannot be enabled again for that kernel (also not via cmdline an attacker could modify to reboot into a system with the option for a crashkernel). Disabling kdump in the kernel when secretmem pages are allocated is one approach, although sub-optimal.
more risky it gets. However during reboot/normal kexec() we should do some cleanup, it makes sense and secretmem can indeed be useful in that case. Regarding loading custom kexec() kernels, we mitigate this with the kexec file-based API where we can verify the signature of the loaded kimage (assuming the system runs a kernel provided by a trusted 3rd party and we 've maintained a chain of trust since booting).
For example in VMs (like QEMU), we often don't clear physical memory during a reboot. So if an attacker manages to load a kernel that you can trick into reading random physical memory areas, we can leak secretmem data I think.
And there might be ways to achieve that just using the cmdline, not necessarily loading a different kernel. For example if you limit the kernel footprint ("mem=256M") and disable strict_iomem_checks ("strict_iomem_checks=relaxed") you can just extract that memory via /dev/mem if I am not wrong.
So as an attacker, modify the (grub) cmdline to "mem=256M strict_iomem_checks=relaxed", reboot, and read all memory via /dev/mem. Or load a signed kexec kernel with that cmdline and boot into it.
Interesting problem :)
On Thu, May 06, 2021 at 08:26:41AM -0700, James Bottomley wrote:
On Wed, 2021-05-05 at 12:08 -0700, Andrew Morton wrote:
On Wed, 3 Mar 2021 18:22:00 +0200 Mike Rapoport rppt@kernel.org wrote:
This is an implementation of "secret" mappings backed by a file descriptor.
tl;dr: I like this series, I think there are number of clarifications needed, though. See below.
The file descriptor backing secret memory mappings is created using a dedicated memfd_secret system call The desired protection mode for the memory is configured using flags parameter of the system call. The mmap() of the file descriptor created with memfd_secret() will create a "secret" memory mapping. The pages in that mapping will be marked as not present in the direct map and will be present only in the page table of the owning mm.
Although normally Linux userspace mappings are protected from other users, such secret mappings are useful for environments where a hostile tenant is trying to trick the kernel into giving them access to other tenants mappings.
I continue to struggle with this and I don't recall seeing much enthusiasm from others. Perhaps we're all missing the value point and some additional selling is needed.
Am I correct in understanding that the overall direction here is to protect keys (and perhaps other things) from kernel bugs? That if the kernel was bug-free then there would be no need for this feature? If so, that's a bit sad. But realistic I guess.
Secret memory really serves several purposes. The "increase the level of difficulty of secret exfiltration" you describe. And, as you say, if the kernel were bug free this wouldn't be necessary.
But also:
- Memory safety for user space code. Once the secret memory is allocated, the user can't accidentally pass it into the kernel to be transmitted somewhere.
In my first read through, I didn't see how cross-userspace operations were blocked, but it looks like it's the various gup paths where {vma,page}_is_secretmem() is called. (Thank you for the self-test! That helped me follow along.) I think this access pattern should be more clearly spelled out in the cover later (i.e. "This will block things like process_vm_readv()").
I like the results (inaccessible outside the process), though I suspect this will absolutely melt gdb or other ptracers that try to see into the memory. Don't get me wrong, I'm a big fan of such concepts[0], but I see nothing in the cover letter about it (e.g. the effects on "ptrace" or "gdb" are not mentioned.)
There is also a risk here of this becoming a forensics nightmare: userspace malware will just download their entire executable region into a memfd_secret region. Can we, perhaps, disallow mmap/mprotect with PROT_EXEC when vma_is_secretmem()? The OpenSSL example, for example, certainly doesn't need PROT_EXEC.
What's happening with O_CLOEXEC in this code? I don't see that mentioned in the cover letter either. Why is it disallowed? That seems a strange limitation for something trying to avoid leaking secrets into other processes.
And just so I'm sure I understand: if a vma_is_secretmem() check is missed in future mm code evolutions, it seems there is nothing to block the kernel from accessing the contents directly through copy_from_user() via the userspace virtual address, yes?
- It also serves as a basis for context protection of virtual machines, but other groups are working on this aspect, and it is broadly similar to the secret exfiltration from the kernel problem.
Is this intended to protect keys/etc after the attacker has gained the ability to run arbitrary kernel-mode code? If so, that seems optimistic, doesn't it?
Not exactly: there are many types of kernel attack, but mostly the attacker either manages to effect a privilege escalation to root or gets the ability to run a ROP gadget. The object of this code is to be completely secure against root trying to extract the secret (some what similar to the lockdown idea), thus defeating privilege escalation and to provide "sufficient" protection against ROP gadgets.
The ROP gadget thing needs more explanation: the usual defeatist approach is to say that once the attacker gains the stack, they can do anything because they can find enough ROP gadgets to be turing complete. However, in the real world, given the kernel stack size limit and address space layout randomization making finding gadgets really hard, usually the attacker gets one or at most two gadgets to string together. Not having any in-kernel primitive for accessing secret memory means the one gadget ROP attack can't work. Since the only way to access secret memory is to reconstruct the missing mapping entry, the attacker has to recover the physical page and insert a PTE pointing to it in the kernel and then retrieve the contents. That takes at least three gadgets which is a level of difficulty beyond most standard attacks.
As for protecting against exploited kernel flaws I also see benefits here. While the kernel is already blocked from directly reading contents from userspace virtual addresses (i.e. SMAP), this feature does help by blocking the kernel from directly reading contents via the direct map alias. (i.e. this feature is a specialized version of XPFO[1], which tried to do this for ALL user memory.) So in that regard, yes, this has value in the sense that to perform exfiltration, an attacker would need a significant level of control over kernel execution or over page table contents.
Sufficient control over PTE allocation and positioning is possible without kernel execution control[3], and "only" having an arbitrary write primitive can lead to direct PTE control. Because of this, it would be nice to have page tables strongly protected[2] in the kernel. They remain a viable "data only" attack given a sufficiently "capable" write flaw.
I would argue that page table entries are a more important asset to protect than userspace secrets, but given the difficulties with XPFO and the not-yet-available PKS I can understand starting here. It does, absolutely, narrow the ways exploits must be written to exfiltrate secret contents. (We are starting to now constrict[4] many attack methods into attacking the page table itself, which is good in the sense that protecting page tables will be a big win, and bad in the sense that focusing attack research on page tables means we're going to see some very powerful attacks.)
I think that a very complete description of the threats which this feature addresses would be helpful.
It's designed to protect against three different threats:
- Detection of user secret memory mismanagement
I would say "cross-process secret userspace memory exposures" (via a number of common interfaces by blocking it at the GUP level).
- significant protection against privilege escalation
I don't see how this series protects against privilege escalation. (It protects against exfiltration.) Maybe you mean include this in the first bullet point (i.e. "cross-process secret userspace memory exposures, even in the face of privileged processes")?
- enhanced protection (in conjunction with all the other in-kernel attack prevention systems) against ROP attacks.
Same here, I don't see it preventing ROP, but I see it making "simple" ROP insufficient to perform exfiltration.
-Kees
[0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/secu... [1] https://lore.kernel.org/linux-mm/cover.1554248001.git.khalid.aziz@oracle.com... [2] https://lore.kernel.org/lkml/20210505003032.489164-1-rick.p.edgecombe@intel.... [3] https://googleprojectzero.blogspot.com/2015/03/exploiting-dram-rowhammer-bug... [4] https://git.kernel.org/linus/cf68fffb66d60d96209446bfc4a15291dc5a5d41
On Thu, 2021-05-06 at 10:33 -0700, Kees Cook wrote:
On Thu, May 06, 2021 at 08:26:41AM -0700, James Bottomley wrote:
[...]
- Memory safety for user space code. Once the secret memory is allocated, the user can't accidentally pass it into the
kernel to be transmitted somewhere.
In my first read through, I didn't see how cross-userspace operations were blocked, but it looks like it's the various gup paths where {vma,page}_is_secretmem() is called. (Thank you for the self-test! That helped me follow along.) I think this access pattern should be more clearly spelled out in the cover later (i.e. "This will block things like process_vm_readv()").
I'm sure Mike can add it.
I like the results (inaccessible outside the process), though I suspect this will absolutely melt gdb or other ptracers that try to see into the memory.
I wouldn't say "melt" ... one of the Demos we did a FOSDEM was using gdb/ptrace to extract secrets and then showing it couldn't be done if secret memory was used. You can still trace the execution of the process (and thus you could extract the secret as it's processed in registers, for instance) but you just can't extract the actual secret memory contents ... that's a fairly limited and well defined restriction.
Don't get me wrong, I'm a big fan of such concepts[0], but I see nothing in the cover letter about it (e.g. the effects on "ptrace" or "gdb" are not mentioned.)
Sure, but we thought "secret" covered it. It wouldn't be secret if gdb/ptrace from another process could see it.
There is also a risk here of this becoming a forensics nightmare: userspace malware will just download their entire executable region into a memfd_secret region. Can we, perhaps, disallow mmap/mprotect with PROT_EXEC when vma_is_secretmem()? The OpenSSL example, for example, certainly doesn't need PROT_EXEC.
I think disallowing PROT_EXEC is a great enhancement.
What's happening with O_CLOEXEC in this code? I don't see that mentioned in the cover letter either. Why is it disallowed? That seems a strange limitation for something trying to avoid leaking secrets into other processes.
I actually thought we forced it, so I'll let Mike address this. I think allowing it is great, so the secret memory isn't inherited by children, but I can see use cases where a process would want its child to inherit the secrets.
And just so I'm sure I understand: if a vma_is_secretmem() check is missed in future mm code evolutions, it seems there is nothing to block the kernel from accessing the contents directly through copy_from_user() via the userspace virtual address, yes?
Technically no because copy_from_user goes via the userspace page tables which do have access.
- It also serves as a basis for context protection of virtual machines, but other groups are working on this aspect, and it
is broadly similar to the secret exfiltration from the kernel problem.
Is this intended to protect keys/etc after the attacker has gained the ability to run arbitrary kernel-mode code? If so, that seems optimistic, doesn't it?
Not exactly: there are many types of kernel attack, but mostly the attacker either manages to effect a privilege escalation to root or gets the ability to run a ROP gadget. The object of this code is to be completely secure against root trying to extract the secret (some what similar to the lockdown idea), thus defeating privilege escalation and to provide "sufficient" protection against ROP gadgets.
The ROP gadget thing needs more explanation: the usual defeatist approach is to say that once the attacker gains the stack, they can do anything because they can find enough ROP gadgets to be turing complete. However, in the real world, given the kernel stack size limit and address space layout randomization making finding gadgets really hard, usually the attacker gets one or at most two gadgets to string together. Not having any in-kernel primitive for accessing secret memory means the one gadget ROP attack can't work. Since the only way to access secret memory is to reconstruct the missing mapping entry, the attacker has to recover the physical page and insert a PTE pointing to it in the kernel and then retrieve the contents. That takes at least three gadgets which is a level of difficulty beyond most standard attacks.
As for protecting against exploited kernel flaws I also see benefits here. While the kernel is already blocked from directly reading contents from userspace virtual addresses (i.e. SMAP), this feature does help by blocking the kernel from directly reading contents via the direct map alias. (i.e. this feature is a specialized version of XPFO[1], which tried to do this for ALL user memory.) So in that regard, yes, this has value in the sense that to perform exfiltration, an attacker would need a significant level of control over kernel execution or over page table contents.
Sufficient control over PTE allocation and positioning is possible without kernel execution control[3], and "only" having an arbitrary write primitive can lead to direct PTE control. Because of this, it would be nice to have page tables strongly protected[2] in the kernel. They remain a viable "data only" attack given a sufficiently "capable" write flaw.
Right, but this is on the radar of several people and when fixed will strengthen the value of secret memory.
I would argue that page table entries are a more important asset to protect than userspace secrets, but given the difficulties with XPFO and the not-yet-available PKS I can understand starting here. It does, absolutely, narrow the ways exploits must be written to exfiltrate secret contents. (We are starting to now constrict[4] many attack methods into attacking the page table itself, which is good in the sense that protecting page tables will be a big win, and bad in the sense that focusing attack research on page tables means we're going to see some very powerful attacks.)
I think that a very complete description of the threats which this feature addresses would be helpful.
It's designed to protect against three different threats:
- Detection of user secret memory mismanagement
I would say "cross-process secret userspace memory exposures" (via a number of common interfaces by blocking it at the GUP level).
- significant protection against privilege escalation
I don't see how this series protects against privilege escalation. (It protects against exfiltration.) Maybe you mean include this in the first bullet point (i.e. "cross-process secret userspace memory exposures, even in the face of privileged processes")?
It doesn't prevent privilege escalation from happening in the first place, but once the escalation has happened it protects against exfiltration by the newly minted root attacker.
- enhanced protection (in conjunction with all the other in-
kernel attack prevention systems) against ROP attacks.
Same here, I don't see it preventing ROP, but I see it making "simple" ROP insufficient to perform exfiltration.
Right, that's why I call it "enhanced protection". With ROP the design goal is to take exfiltration beyond the simple, and require increasing complexity in the attack ... the usual security whack-a-mole approach ... in the hope that script kiddies get bored by the level of difficulty and move on to something easier.
James
On Thu, May 06, 2021 at 11:47:47AM -0700, James Bottomley wrote:
On Thu, 2021-05-06 at 10:33 -0700, Kees Cook wrote:
On Thu, May 06, 2021 at 08:26:41AM -0700, James Bottomley wrote:
[...]
I think that a very complete description of the threats which this feature addresses would be helpful.
It's designed to protect against three different threats:
- Detection of user secret memory mismanagement
I would say "cross-process secret userspace memory exposures" (via a number of common interfaces by blocking it at the GUP level).
- significant protection against privilege escalation
I don't see how this series protects against privilege escalation. (It protects against exfiltration.) Maybe you mean include this in the first bullet point (i.e. "cross-process secret userspace memory exposures, even in the face of privileged processes")?
It doesn't prevent privilege escalation from happening in the first place, but once the escalation has happened it protects against exfiltration by the newly minted root attacker.
So, after thinking a bit more about this, I don't think there is protection here against privileged execution. This feature kind of helps against cross-process read/write attempts, but it doesn't help with sufficiently privileged (i.e. ptraced) execution, since we can just ask the process itself to do the reading:
$ gdb ./memfd_secret ... ready: 0x7ffff7ffb000 Breakpoint 1, ... (gdb) compile code unsigned long addr = 0x7ffff7ffb000UL; printf("%016lx\n", *((unsigned long *)addr)); 55555555555555555
And since process_vm_readv() requires PTRACE_ATTACH, there's very little difference in effort between process_vm_readv() and the above.
So, what other paths through GUP exist that aren't covered by PTRACE_ATTACH? And if none, then should this actually just be done by setting the process undumpable? (This is already what things like gnupg do.)
So, the user-space side of this doesn't seem to really help. The kernel side protection is interesting for kernel read/write flaws, though, in the sense that the process is likely not being attacked from "current", so a kernel-side attack would need to either walk the page tables and create new ones, or spawn a new userspace process to do the ptracing.
So, while I like the idea of this stuff, and I see how it provides certain coverages, I'm curious to learn more about the threat model to make sure it's actually providing meaningful hurdles to attacks.
On Thu, May 06, 2021 at 11:47:47AM -0700, James Bottomley wrote:
On Thu, 2021-05-06 at 10:33 -0700, Kees Cook wrote:
On Thu, May 06, 2021 at 08:26:41AM -0700, James Bottomley wrote:
What's happening with O_CLOEXEC in this code? I don't see that mentioned in the cover letter either. Why is it disallowed? That seems a strange limitation for something trying to avoid leaking secrets into other processes.
I actually thought we forced it, so I'll let Mike address this. I think allowing it is great, so the secret memory isn't inherited by children, but I can see use cases where a process would want its child to inherit the secrets.
We do not enforce O_CLOEXEC, but if the user explicitly requested O_CLOEXEC it would be passed to get_unused_fd_flags().
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