Commit 07f146f5 authored by Dave Hansen's avatar Dave Hansen Committed by Ingo Molnar

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: default avatarDave Hansen <>
Reviewed-by: default avatarThomas Gleixner <>
Cc: Andrew Morton <>
Cc: Andy Lutomirski <>
Cc: Borislav Petkov <>
Cc: Brian Gerst <>
Cc: Dave Hansen <>
Cc: Denys Vlasenko <>
Cc: H. Peter Anvin <>
Cc: Linus Torvalds <>
Cc: Peter Zijlstra <>
Cc: Rik van Riel <>
Link: default avatarIngo Molnar <>
parent 1b2ee126
......@@ -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: */
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