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, 13 insertions, 3 deletions

diff --git a/include/asm-x86/pgtable.h b/include/asm-x86/pgtable.h
index 801b31f71452..55c3a0e3a8ce 100644
--- a/include/asm-x86/pgtable.h
+++ b/include/asm-x86/pgtable.h
@@ -57,7 +57,8 @@
 #define _KERNPG_TABLE   (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED |    \
                          _PAGE_DIRTY)
 
-#define _PAGE_CHG_MASK  (PTE_MASK | _PAGE_ACCESSED | _PAGE_DIRTY)
+#define _PAGE_CHG_MASK  (PTE_MASK | _PAGE_PCD | _PAGE_PWT |             \
+                         _PAGE_ACCESSED | _PAGE_DIRTY)
 
 #define _PAGE_CACHE_MASK        (_PAGE_PCD | _PAGE_PWT)
 #define _PAGE_CACHE_WB          (0)
@@ -288,12 +289,21 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
          * Chop off the NX bit (if present), and add the NX portion of
          * the newprot (if present):
          */
-        val &= _PAGE_CHG_MASK & ~_PAGE_NX;
-        val |= pgprot_val(newprot) & __supported_pte_mask;
+        val &= _PAGE_CHG_MASK;
+        val |= pgprot_val(newprot) & (~_PAGE_CHG_MASK) & __supported_pte_mask;
 
         return __pte(val);
 }
 
+/* mprotect needs to preserve PAT bits when updating vm_page_prot */
+#define pgprot_modify pgprot_modify
+static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
+{
+        pgprotval_t preservebits = pgprot_val(oldprot) & _PAGE_CHG_MASK;
+        pgprotval_t addbits = pgprot_val(newprot);
+        return __pgprot(preservebits | addbits);
+}
+
 #define pte_pgprot(x) __pgprot(pte_val(x) & (0xfff | _PAGE_NX))
 
 #define canon_pgprot(p) __pgprot(pgprot_val(p) & __supported_pte_mask)