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>
static inline bool bad_area_access_from_pkeys(unsigned long error_code,
struct vm_area_struct *vma)
{
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;
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;
static inline int
access_error(unsigned long error_code, struct vm_area_struct *vma)
{
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
/*
* Access or read was blocked by protection keys. We do
* this check before any others because we do not want
*/
if (error_code & PF_PK)
return 1;
*/
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: */
if (error_code & PF_WRITE) {
/* write, present and write, not present: */