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Subject[ 05/85] ARM: 7487/1: mm: avoid setting nG bit for user mappings that arent present
Date
From: Greg KH <gregkh@linuxfoundation.org>

3.4-stable review patch. If anyone has any objections, please let me know.

------------------

From: Will Deacon <will.deacon@arm.com>

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm/include/asm/pgtable.h | 34 ++++++++++++++++++----------------
arch/arm/mm/flush.c | 2 --
2 files changed, 18 insertions(+), 18 deletions(-)

--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -195,6 +195,18 @@ static inline pte_t *pmd_page_vaddr(pmd_

#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)
{
@@ -206,25 +218,15 @@ extern void __sync_icache_dcache(pte_t p
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; }
--- a/arch/arm/mm/flush.c
+++ b/arch/arm/mm/flush.c
@@ -231,8 +231,6 @@ 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;



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