Commit-ID: 07f146f53e8de826e4afa3a88ea65bdb13c24959
Gitweb: http://git.kernel.org/tip/07f146f53e8de826e4afa3a88ea65bdb13c24959
Author: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
AuthorDate: Fri, 12 Feb 2016 13:02:22 -0800
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 18 Feb 2016 19:46:28 +0100
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@xxxxxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Link: http://lkml.kernel.org/r/20160212210222.EBB63D8C@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/mm/fault.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 319331a..68ecdff 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: */
--
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