The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: ea72ce5da22806d5713f3ffb39a6d5ae73841f93 Gitweb: https://git.kernel.org/tip/ea72ce5da22806d5713f3ffb39a6d5ae73841f93 Author: Thomas Gleixner tglx@linutronix.de AuthorDate: Wed, 14 Aug 2024 00:29:36 +02:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Tue, 20 Aug 2024 13:44:57 +02:00

x86/kaslr: Expose and use the end of the physical memory address space

iounmap() on x86 occasionally fails to unmap because the provided valid ioremap address is not below high_memory. It turned out that this happens due to KASLR.

KASLR uses the full address space between PAGE_OFFSET and vaddr_end to randomize the starting points of the direct map, vmalloc and vmemmap regions. It thereby limits the size of the direct map by using the installed memory size plus an extra configurable margin for hot-plug memory. This limitation is done to gain more randomization space because otherwise only the holes between the direct map, vmalloc, vmemmap and vaddr_end would be usable for randomizing.

The limited direct map size is not exposed to the rest of the kernel, so the memory hot-plug and resource management related code paths still operate under the assumption that the available address space can be determined with MAX_PHYSMEM_BITS.

request_free_mem_region() allocates from (1 << MAX_PHYSMEM_BITS) - 1 downwards. That means the first allocation happens past the end of the direct map and if unlucky this address is in the vmalloc space, which causes high_memory to become greater than VMALLOC_START and consequently causes iounmap() to fail for valid ioremap addresses.

MAX_PHYSMEM_BITS cannot be changed for that because the randomization does not align with address bit boundaries and there are other places which actually require to know the maximum number of address bits. All remaining usage sites of MAX_PHYSMEM_BITS have been analyzed and found to be correct.

Cure this by exposing the end of the direct map via PHYSMEM_END and use that for the memory hot-plug and resource management related places instead of relying on MAX_PHYSMEM_BITS. In the KASLR case PHYSMEM_END maps to a variable which is initialized by the KASLR initialization and otherwise it is based on MAX_PHYSMEM_BITS as before.

To prevent future hickups add a check into add_pages() to catch callers trying to add memory above PHYSMEM_END.

Fixes: 0483e1fa6e09 ("x86/mm: Implement ASLR for kernel memory regions") Reported-by: Max Ramanouski max8rr8@gmail.com Reported-by: Alistair Popple apopple@nvidia.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-By: Max Ramanouski max8rr8@gmail.com Tested-by: Alistair Popple apopple@nvidia.com Reviewed-by: Dan Williams dan.j.williams@intel.com Reviewed-by: Alistair Popple apopple@nvidia.com Reviewed-by: Kees Cook kees@kernel.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/87ed6soy3z.ffs@tglx --- arch/x86/include/asm/page_64.h | 1 +- arch/x86/include/asm/pgtable_64_types.h | 4 +++- arch/x86/mm/init_64.c | 4 +++- arch/x86/mm/kaslr.c | 32 +++++++++++++++++++----- include/linux/mm.h | 4 +++- kernel/resource.c | 6 +---- mm/memory_hotplug.c | 2 +- mm/sparse.c | 2 +- 8 files changed, 43 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h index af4302d..f3d257c 100644 --- a/arch/x86/include/asm/page_64.h +++ b/arch/x86/include/asm/page_64.h @@ -17,6 +17,7 @@ extern unsigned long phys_base; extern unsigned long page_offset_base; extern unsigned long vmalloc_base; extern unsigned long vmemmap_base; +extern unsigned long physmem_end;

static __always_inline unsigned long __phys_addr_nodebug(unsigned long x) { diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h index 9053dfe..a98e534 100644 --- a/arch/x86/include/asm/pgtable_64_types.h +++ b/arch/x86/include/asm/pgtable_64_types.h @@ -140,6 +140,10 @@ extern unsigned int ptrs_per_p4d; # define VMEMMAP_START __VMEMMAP_BASE_L4 #endif /* CONFIG_DYNAMIC_MEMORY_LAYOUT */

+#ifdef CONFIG_RANDOMIZE_MEMORY +# define PHYSMEM_END physmem_end +#endif + /* * End of the region for which vmalloc page tables are pre-allocated. * For non-KMSAN builds, this is the same as VMALLOC_END. diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index d8dbeac..ff25364 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -958,8 +958,12 @@ static void update_end_of_memory_vars(u64 start, u64 size) int add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages, struct mhp_params *params) { + unsigned long end = ((start_pfn + nr_pages) << PAGE_SHIFT) - 1; int ret;

+ if (WARN_ON_ONCE(end > PHYSMEM_END)) + return -ERANGE; + ret = __add_pages(nid, start_pfn, nr_pages, params); WARN_ON_ONCE(ret);

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index 37db264..230f1de 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -47,13 +47,24 @@ static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE; */ static __initdata struct kaslr_memory_region { unsigned long *base; + unsigned long *end; unsigned long size_tb; } kaslr_regions[] = { - { &page_offset_base, 0 }, - { &vmalloc_base, 0 }, - { &vmemmap_base, 0 }, + { + .base = &page_offset_base, + .end = &physmem_end, + }, + { + .base = &vmalloc_base, + }, + { + .base = &vmemmap_base, + }, };

+/* The end of the possible address space for physical memory */ +unsigned long physmem_end __ro_after_init; + /* Get size in bytes used by the memory region */ static inline unsigned long get_padding(struct kaslr_memory_region *region) { @@ -82,6 +93,8 @@ void __init kernel_randomize_memory(void) BUILD_BUG_ON(vaddr_end != CPU_ENTRY_AREA_BASE); BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);

+ /* Preset the end of the possible address space for physical memory */ + physmem_end = ((1ULL << MAX_PHYSMEM_BITS) - 1); if (!kaslr_memory_enabled()) return;

@@ -128,11 +141,18 @@ void __init kernel_randomize_memory(void) vaddr += entropy; *kaslr_regions[i].base = vaddr;

+ /* Calculate the end of the region */ + vaddr += get_padding(&kaslr_regions[i]); /* - * Jump the region and add a minimum padding based on - * randomization alignment. + * KASLR trims the maximum possible size of the + * direct-map. Update the physmem_end boundary. + * No rounding required as the region starts + * PUD aligned and size is in units of TB. */ - vaddr += get_padding(&kaslr_regions[i]); + if (kaslr_regions[i].end) + *kaslr_regions[i].end = __pa_nodebug(vaddr - 1); + + /* Add a minimum padding based on randomization alignment. */ vaddr = round_up(vaddr + 1, PUD_SIZE); remain_entropy -= entropy; } diff --git a/include/linux/mm.h b/include/linux/mm.h index c4b238a..b386415 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -97,6 +97,10 @@ extern const int mmap_rnd_compat_bits_max; extern int mmap_rnd_compat_bits __read_mostly; #endif

+#ifndef PHYSMEM_END +# define PHYSMEM_END ((1ULL << MAX_PHYSMEM_BITS) - 1) +#endif + #include <asm/page.h> #include <asm/processor.h>

diff --git a/kernel/resource.c b/kernel/resource.c index 14777af..a83040f 100644 --- a/kernel/resource.c +++ b/kernel/resource.c @@ -1826,8 +1826,7 @@ static resource_size_t gfr_start(struct resource *base, resource_size_t size, if (flags & GFR_DESCENDING) { resource_size_t end;

- end = min_t(resource_size_t, base->end, - (1ULL << MAX_PHYSMEM_BITS) - 1); + end = min_t(resource_size_t, base->end, PHYSMEM_END); return end - size + 1; }

@@ -1844,8 +1843,7 @@ static bool gfr_continue(struct resource *base, resource_size_t addr, * @size did not wrap 0. */ return addr > addr - size && - addr <= min_t(resource_size_t, base->end, - (1ULL << MAX_PHYSMEM_BITS) - 1); + addr <= min_t(resource_size_t, base->end, PHYSMEM_END); }

static resource_size_t gfr_next(resource_size_t addr, resource_size_t size, diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 66267c2..951878a 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1681,7 +1681,7 @@ struct range __weak arch_get_mappable_range(void)

struct range mhp_get_pluggable_range(bool need_mapping) { - const u64 max_phys = (1ULL << MAX_PHYSMEM_BITS) - 1; + const u64 max_phys = PHYSMEM_END; struct range mhp_range;

if (need_mapping) { diff --git a/mm/sparse.c b/mm/sparse.c index e4b8300..0c3bff8 100644 --- a/mm/sparse.c +++ b/mm/sparse.c @@ -129,7 +129,7 @@ static inline int sparse_early_nid(struct mem_section *section) static void __meminit mminit_validate_memmodel_limits(unsigned long *start_pfn, unsigned long *end_pfn) { - unsigned long max_sparsemem_pfn = 1UL << (MAX_PHYSMEM_BITS-PAGE_SHIFT); + unsigned long max_sparsemem_pfn = (PHYSMEM_END + 1) >> PAGE_SHIFT;

/* * Sanity checks - do not allow an architecture to pass