4.17-stable review patch. If anyone has any objections, please let me know.
------------------
From: Dave Hansen dave.hansen@linux.intel.com
commit eac7073aa69aa1cac819aa712146284f53f642b1 upstream.
The kernel image starts out with the Global bit set across the entire kernel image. The bit is cleared with set_memory_nonglobal() in the configurations with PCIDs where the performance benefits of the Global bit are not needed.
However, this is fragile. It means that we are stuck opting *out* of the less-secure (Global bit set) configuration, which seems backwards. Let's start more secure (Global bit clear) and then let things opt back in if they want performance, or are truly mapping common data between kernel and userspace.
This fixes a bug. Before this patch, there are areas that are unmapped from the user page tables (like like everything above 0xffffffff82600000 in the example below). These have the hallmark of being a wrong Global area: they are not identical in the 'current_kernel' and 'current_user' page table dumps. They are also read-write, which means they're much more likely to contain secrets.
Before this patch:
current_kernel:---[ High Kernel Mapping ]--- current_kernel-0xffffffff80000000-0xffffffff81000000 16M pmd current_kernel-0xffffffff81000000-0xffffffff81e00000 14M ro PSE GLB x pmd current_kernel-0xffffffff81e00000-0xffffffff81e11000 68K ro GLB x pte current_kernel-0xffffffff81e11000-0xffffffff82000000 1980K RW GLB NX pte current_kernel-0xffffffff82000000-0xffffffff82600000 6M ro PSE GLB NX pmd current_kernel-0xffffffff82600000-0xffffffff82c00000 6M RW PSE GLB NX pmd current_kernel-0xffffffff82c00000-0xffffffff82e00000 2M RW GLB NX pte current_kernel-0xffffffff82e00000-0xffffffff83200000 4M RW PSE GLB NX pmd current_kernel-0xffffffff83200000-0xffffffffa0000000 462M pmd
current_user:---[ High Kernel Mapping ]--- current_user-0xffffffff80000000-0xffffffff81000000 16M pmd current_user-0xffffffff81000000-0xffffffff81e00000 14M ro PSE GLB x pmd current_user-0xffffffff81e00000-0xffffffff81e11000 68K ro GLB x pte current_user-0xffffffff81e11000-0xffffffff82000000 1980K RW GLB NX pte current_user-0xffffffff82000000-0xffffffff82600000 6M ro PSE GLB NX pmd current_user-0xffffffff82600000-0xffffffffa0000000 474M pmd
After this patch:
current_kernel:---[ High Kernel Mapping ]--- current_kernel-0xffffffff80000000-0xffffffff81000000 16M pmd current_kernel-0xffffffff81000000-0xffffffff81e00000 14M ro PSE GLB x pmd current_kernel-0xffffffff81e00000-0xffffffff81e11000 68K ro GLB x pte current_kernel-0xffffffff81e11000-0xffffffff82000000 1980K RW NX pte current_kernel-0xffffffff82000000-0xffffffff82600000 6M ro PSE GLB NX pmd current_kernel-0xffffffff82600000-0xffffffff82c00000 6M RW PSE NX pmd current_kernel-0xffffffff82c00000-0xffffffff82e00000 2M RW NX pte current_kernel-0xffffffff82e00000-0xffffffff83200000 4M RW PSE NX pmd current_kernel-0xffffffff83200000-0xffffffffa0000000 462M pmd
current_user:---[ High Kernel Mapping ]--- current_user-0xffffffff80000000-0xffffffff81000000 16M pmd current_user-0xffffffff81000000-0xffffffff81e00000 14M ro PSE GLB x pmd current_user-0xffffffff81e00000-0xffffffff81e11000 68K ro GLB x pte current_user-0xffffffff81e11000-0xffffffff82000000 1980K RW NX pte current_user-0xffffffff82000000-0xffffffff82600000 6M ro PSE GLB NX pmd current_user-0xffffffff82600000-0xffffffffa0000000 474M pmd
Fixes: 0f561fce4d69 ("x86/pti: Enable global pages for shared areas") Reported-by: Hugh Dickins hughd@google.com Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: keescook@google.com Cc: aarcange@redhat.com Cc: jgross@suse.com Cc: jpoimboe@redhat.com Cc: gregkh@linuxfoundation.org Cc: peterz@infradead.org Cc: torvalds@linux-foundation.org Cc: bp@alien8.de Cc: luto@kernel.org Cc: ak@linux.intel.com Cc: Kees Cook keescook@google.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Juergen Gross jgross@suse.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Borislav Petkov bp@alien8.de Cc: Andy Lutomirski luto@kernel.org Cc: Andi Kleen ak@linux.intel.com Link: https://lkml.kernel.org/r/20180802225825.A100C071@viggo.jf.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/mm/pageattr.c | 6 ++++++ arch/x86/mm/pti.c | 34 ++++++++++++++++++++++++---------- 2 files changed, 30 insertions(+), 10 deletions(-)
--- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -1784,6 +1784,12 @@ int set_memory_nonglobal(unsigned long a __pgprot(_PAGE_GLOBAL), 0); }
+int set_memory_global(unsigned long addr, int numpages) +{ + return change_page_attr_set(&addr, numpages, + __pgprot(_PAGE_GLOBAL), 0); +} + static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc) { struct cpa_data cpa; --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -436,6 +436,13 @@ static inline bool pti_kernel_image_glob }
/* + * This is the only user for these and it is not arch-generic + * like the other set_memory.h functions. Just extern them. + */ +extern int set_memory_nonglobal(unsigned long addr, int numpages); +extern int set_memory_global(unsigned long addr, int numpages); + +/* * For some configurations, map all of kernel text into the user page * tables. This reduces TLB misses, especially on non-PCID systems. */ @@ -447,7 +454,8 @@ void pti_clone_kernel_text(void) * clone the areas past rodata, they might contain secrets. */ unsigned long start = PFN_ALIGN(_text); - unsigned long end = (unsigned long)__end_rodata_hpage_align; + unsigned long end_clone = (unsigned long)__end_rodata_hpage_align; + unsigned long end_global = PFN_ALIGN((unsigned long)__stop___ex_table);
if (!pti_kernel_image_global_ok()) return; @@ -459,14 +467,18 @@ void pti_clone_kernel_text(void) * pti_set_kernel_image_nonglobal() did to clear the * global bit. */ - pti_clone_pmds(start, end, _PAGE_RW); + pti_clone_pmds(start, end_clone, _PAGE_RW); + + /* + * pti_clone_pmds() will set the global bit in any PMDs + * that it clones, but we also need to get any PTEs in + * the last level for areas that are not huge-page-aligned. + */ + + /* Set the global bit for normal non-__init kernel text: */ + set_memory_global(start, (end_global - start) >> PAGE_SHIFT); }
-/* - * This is the only user for it and it is not arch-generic like - * the other set_memory.h functions. Just extern it. - */ -extern int set_memory_nonglobal(unsigned long addr, int numpages); void pti_set_kernel_image_nonglobal(void) { /* @@ -478,9 +490,11 @@ void pti_set_kernel_image_nonglobal(void unsigned long start = PFN_ALIGN(_text); unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE);
- if (pti_kernel_image_global_ok()) - return; - + /* + * This clears _PAGE_GLOBAL from the entire kernel image. + * pti_clone_kernel_text() map put _PAGE_GLOBAL back for + * areas that are mapped to userspace. + */ set_memory_nonglobal(start, (end - start) >> PAGE_SHIFT); }