ARM: 7487/1: mm: avoid setting nG bit for user mappings that aren't present

commit 47f1204329237a0f8655f5a9f14a38ac81946ca1 upstream.

Swap entries are encoding in ptes such that !pte_present(pte) and
pte_file(pte). The remaining bits of the descriptor are used to identify
the swapfile and offset within it to the swap entry.

When writing such a pte for a user virtual address, set_pte_at
unconditionally sets the nG bit, which (in the case of LPAE) will
corrupt the swapfile offset and lead to a BUG:

[  140.494067] swap_free: Unused swap offset entry 000763b4
[  140.509989] BUG: Bad page map in process rs:main Q:Reg  pte:0ec76800 pmd:8f92e003

This patch fixes the problem by only setting the nG bit for user
mappings that are actually present.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index 8512475..9b419ab 100644 (file)
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -232,6 +232,18 @@ static inline pte_t *pmd_page_vaddr(pmd_t pmd)
 #define set_pte_ext(ptep,pte,ext) cpu_set_pte_ext(ptep,pte,ext)
 #define pte_clear(mm,addr,ptep)        set_pte_ext(ptep, __pte(0), 0)
 
+#define pte_none(pte)          (!pte_val(pte))
+#define pte_present(pte)       (pte_val(pte) & L_PTE_PRESENT)
+#define pte_write(pte)         (!(pte_val(pte) & L_PTE_RDONLY))
+#define pte_dirty(pte)         (pte_val(pte) & L_PTE_DIRTY)
+#define pte_young(pte)         (pte_val(pte) & L_PTE_YOUNG)
+#define pte_exec(pte)          (!(pte_val(pte) & L_PTE_XN))
+#define pte_special(pte)       (0)
+
+#define pte_present_user(pte) \
+       ((pte_val(pte) & (L_PTE_PRESENT | L_PTE_USER)) == \
+        (L_PTE_PRESENT | L_PTE_USER))
+
 #if __LINUX_ARM_ARCH__ < 6
 static inline void __sync_icache_dcache(pte_t pteval)
 {
@@ -243,25 +255,15 @@ extern void __sync_icache_dcache(pte_t pteval);
 static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
                              pte_t *ptep, pte_t pteval)
 {
-       if (addr >= TASK_SIZE)
-               set_pte_ext(ptep, pteval, 0);
-       else {
+       unsigned long ext = 0;
+
+       if (addr < TASK_SIZE && pte_present_user(pteval)) {
                __sync_icache_dcache(pteval);
-               set_pte_ext(ptep, pteval, PTE_EXT_NG);
+               ext |= PTE_EXT_NG;
        }
-}
 
-#define pte_none(pte)          (!pte_val(pte))
-#define pte_present(pte)       (pte_val(pte) & L_PTE_PRESENT)
-#define pte_write(pte)         (!(pte_val(pte) & L_PTE_RDONLY))
-#define pte_dirty(pte)         (pte_val(pte) & L_PTE_DIRTY)
-#define pte_young(pte)         (pte_val(pte) & L_PTE_YOUNG)
-#define pte_exec(pte)          (!(pte_val(pte) & L_PTE_XN))
-#define pte_special(pte)       (0)
-
-#define pte_present_user(pte) \
-       ((pte_val(pte) & (L_PTE_PRESENT | L_PTE_USER)) == \
-        (L_PTE_PRESENT | L_PTE_USER))
+       set_pte_ext(ptep, pteval, ext);
+}
 
 #define PTE_BIT_FUNC(fn,op) \
 static inline pte_t pte_##fn(pte_t pte) { pte_val(pte) op; return pte; }

diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
index 1a8d4aa..8fda9f7 100644 (file)
--- a/arch/arm/mm/flush.c
+++ b/arch/arm/mm/flush.c
@@ -236,8 +236,6 @@ void __sync_icache_dcache(pte_t pteval)
        struct page *page;
        struct address_space *mapping;
 
-       if (!pte_present_user(pteval))
-               return;
        if (cache_is_vipt_nonaliasing() && !pte_exec(pteval))
                /* only flush non-aliasing VIPT caches for exec mappings */
                return;