mprotect: prevent alteration of the PAT bits

There is a defect in mprotect, which lets the user change the page cache
type bits by-passing the kernel reserve_memtype and free_memtype
wrappers.  Fix the problem by not letting mprotect change the PAT bits.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 4de546899dc1..a5bf31c27375 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -26,6 +26,13 @@
 #include <asm/cacheflush.h>
 #include <asm/tlbflush.h>
 
+#ifndef pgprot_modify
+static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
+{
+        return newprot;
+}
+#endif
+
 static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
                 unsigned long addr, unsigned long end, pgprot_t newprot,
                 int dirty_accountable)
@@ -192,7 +199,9 @@ success:
          * held in write mode.
          */
         vma->vm_flags = newflags;
-        vma->vm_page_prot = vm_get_page_prot(newflags);
+        vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
+                                          vm_get_page_prot(newflags));
+
         if (vma_wants_writenotify(vma)) {
                 vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
                 dirty_accountable = 1;