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arm64: Introduce execute-only page access permissions

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The ARMv8 architecture allows execute-only user permissions by clearing
the PTE_UXN and PTE_USER bits. However, the kernel running on a CPU
implementation without User Access Override (ARMv8.2 onwards) can still
access such page, so execute-only page permission does not protect
against read(2)/write(2) etc. accesses. Systems requiring such
protection must enable features like SECCOMP.

This patch changes the arm64 __P100 and __S100 protection_map[] macros
to the new __PAGE_EXECONLY attributes. A side effect is that
pte_user() no longer triggers for __PAGE_EXECONLY since PTE_USER isn't
set. To work around this, the check is done on the PTE_NG bit via the
pte_ng() macro. VM_READ is also checked now for page faults.

Reviewed-by: Will Deacon <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
This commit is contained in:
Catalin Marinas 2016-08-11 18:44:50 +01:00 • committed by Will Deacon
commit cab15ce604
4 changed files with 15 additions and 10 deletions
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5
mm/mmap.c
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@ -88,6 +88,11 @@ static void unmap_region(struct mm_struct *mm,
* w: (no) no w: (no) no w: (copy) copy w: (no) no
* x: (no) no x: (no) yes x: (no) yes x: (yes) yes
*
* On arm64, PROT_EXEC has the following behaviour for both MAP_SHARED and
* MAP_PRIVATE:
* r: (no) no
* w: (no) no
* x: (yes) yes
*/
pgprot_t protection_map[16] = {
__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,