[PATCH 4.4 026/163] arm64: Update PTE_RDONLY in set_pte_at() for PROT_NONE permission

From: Greg Kroah-Hartman
Date: Mon May 02 2016 - 21:48:54 EST

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


From: Catalin Marinas <catalin.marinas@xxxxxxx>

commit fdc69e7df3cb24f18a93192641786e5b7ecd1dfe upstream.

The set_pte_at() function must update the hardware PTE_RDONLY bit
depending on the state of the PTE_WRITE and PTE_DIRTY bits of the given
entry value. However, it currently only performs this for pte_valid()
entries, ignoring PTE_PROT_NONE. The side-effect is that PROT_NONE
mappings would not have the PTE_RDONLY bit set. Without
CONFIG_ARM64_HW_AFDBM, this is not an issue since such PROT_NONE pages
are not accessible anyway.

With commit 2f4b829c625e ("arm64: Add support for hardware updates of
the access and dirty pte bits"), the ptep_set_wrprotect() function was
re-written to cope with automatic hardware updates of the dirty state.
As an optimisation, only PTE_RDONLY is checked to assess the "dirty"
status. Since set_pte_at() does not set this bit for PROT_NONE mappings,
such pages may be considered "dirty" as a result of

This patch updates the pte_valid() check to pte_present() in
set_pte_at(). It also adds PTE_PROT_NONE to the swap entry bits comment.

Fixes: 2f4b829c625e ("arm64: Add support for hardware updates of the access and dirty pte bits")
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Reported-by: Ganapatrao Kulkarni <gkulkarni@xxxxxxxxxxxxxxxxxx>
Tested-by: Ganapatrao Kulkarni <gkulkarni@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/arm64/include/asm/pgtable.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -263,7 +263,7 @@ 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 pte)
- if (pte_valid(pte)) {
+ if (pte_present(pte)) {
if (pte_sw_dirty(pte) && pte_write(pte))
pte_val(pte) &= ~PTE_RDONLY;
@@ -640,6 +640,7 @@ extern pgd_t idmap_pg_dir[PTRS_PER_PGD];
* bits 0-1: present (must be zero)
* bits 2-7: swap type
* bits 8-57: swap offset
+ * bit 58: PTE_PROT_NONE (must be zero)
#define __SWP_TYPE_SHIFT 2
#define __SWP_TYPE_BITS 6