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author | Dave Hansen <dave.hansen@linux.intel.com> | 2016-02-13 00:02:22 +0300 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2016-02-18 21:46:28 +0300 |
commit | 07f146f53e8de826e4afa3a88ea65bdb13c24959 (patch) | |
tree | 861b2182fe29fe7924a30e0527a68d62511c1ca9 | |
parent | 1b2ee1266ea647713dbaf44825967c180dfc8d76 (diff) | |
download | linux-07f146f53e8de826e4afa3a88ea65bdb13c24959.tar.xz |
x86/mm/pkeys: Optimize fault handling in access_error()
We might not strictly have to make modifictions to
access_error() to check the VMA here.
If we do not, we will do this:
1. app sets VMA pkey to K
2. app touches a !present page
3. do_page_fault(), allocates and maps page, sets pte.pkey=K
4. return to userspace
5. touch instruction reexecutes, but triggers PF_PK
6. do PKEY signal
What happens with this patch applied:
1. app sets VMA pkey to K
2. app touches a !present page
3. do_page_fault() notices that K is inaccessible
4. do PKEY signal
We basically skip the fault that does an allocation.
So what this lets us do is protect areas from even being
*populated* unless it is accessible according to protection
keys. That seems handy to me and makes protection keys work
more like an mprotect()'d mapping.
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20160212210222.EBB63D8C@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r-- | arch/x86/mm/fault.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 319331afae24..68ecdffe284e 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -900,10 +900,16 @@ bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address) static inline bool bad_area_access_from_pkeys(unsigned long error_code, struct vm_area_struct *vma) { + /* This code is always called on the current mm */ + bool foreign = false; + if (!boot_cpu_has(X86_FEATURE_OSPKE)) return false; if (error_code & PF_PK) return true; + /* this checks permission keys on the VMA: */ + if (!arch_vma_access_permitted(vma, (error_code & PF_WRITE), foreign)) + return true; return false; } @@ -1091,6 +1097,8 @@ int show_unhandled_signals = 1; static inline int access_error(unsigned long error_code, struct vm_area_struct *vma) { + /* This is only called for the current mm, so: */ + bool foreign = false; /* * Access or read was blocked by protection keys. We do * this check before any others because we do not want @@ -1099,6 +1107,13 @@ access_error(unsigned long error_code, struct vm_area_struct *vma) */ if (error_code & PF_PK) return 1; + /* + * Make sure to check the VMA so that we do not perform + * faults just to hit a PF_PK as soon as we fill in a + * page. + */ + if (!arch_vma_access_permitted(vma, (error_code & PF_WRITE), foreign)) + return 1; if (error_code & PF_WRITE) { /* write, present and write, not present: */ |