[PATCH 03/14] powerpc/mm/subpage: Clear RWX bit to indicate no access
From: Aneesh Kumar K.V <hidden>
Date: 2016-03-07 14:10:16
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Michael Ellerman, Linus Torvalds
Subpage protection used to depend on _PAGE_USER bit to implement no access mode. This patch switch that to use _PAGE_RWX. We clear READ and Write access from pte instead of clearing _PAGE_USER now. This was done to enable us to switch to _PAGE_PRIVILGED. subpage_protection() returns the pte bits that need to be cleared. Instead of updating the interface to handle no-access in a separate way, it appears simple to clear RWX acecss to indicate no access. We still don't insert hash pte for these ptes, hence we should not get PROT_FAULT with change. Signed-off-by: Aneesh Kumar K.V <redacted> --- arch/powerpc/mm/hash_utils_64.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index ea23403b3fc0..ec37f4b0a8ff 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c@@ -917,7 +917,7 @@ void demote_segment_4k(struct mm_struct *mm, unsigned long addr) * Userspace sets the subpage permissions using the subpage_prot system call. * * Result is 0: full permissions, _PAGE_RW: read-only, - * _PAGE_USER or _PAGE_USER|_PAGE_RW: no access. + * _PAGE_RWX: no access. */ static int subpage_protection(struct mm_struct *mm, unsigned long ea) {
@@ -943,8 +943,13 @@ static int subpage_protection(struct mm_struct *mm, unsigned long ea) /* extract 2-bit bitfield for this 4k subpage */ spp >>= 30 - 2 * ((ea >> 12) & 0xf); - /* turn 0,1,2,3 into combination of _PAGE_USER and _PAGE_RW */ - spp = ((spp & 2) ? _PAGE_USER : 0) | ((spp & 1) ? _PAGE_RW : 0); + /* + * 0 -> full premission + * 1 -> Read only + * 2 -> no access. + * We return the flag that need to be cleared. + */ + spp = ((spp & 2) ? _PAGE_RWX : 0) | ((spp & 1) ? _PAGE_WRITE : 0); return spp; }
--
2.5.0