[PATCH 4.4 12/96] ARM: 8721/1: mm: dump: check hardware RO bit for LPAE

Greg Kroah-Hartman
2017-11-28T10:28:31Z

From: Philip Derrin <philip@cog.systems>

commit 3b0c0c922ff4be275a8beb87ce5657d16f355b54 upstream.

When CONFIG_ARM_LPAE is set, the PMD dump relies on the software
read-only bit to determine whether a page is writable. This
concealed a bug which left the kernel text section writable
(AP2=0) while marked read-only in the software bit.

In a kernel with the AP2 bug, the dump looks like this:

---[ Kernel Mapping ]---
0xc0000000-0xc0200000 2M RW NX SHD
0xc0200000-0xc0600000 4M ro x SHD
0xc0600000-0xc0800000 2M ro NX SHD
0xc0800000-0xc4800000 64M RW NX SHD

The fix is to check that the software and hardware bits are both
set before displaying "ro". The dump then shows the true perms:

---[ Kernel Mapping ]---
0xc0000000-0xc0200000 2M RW NX SHD
0xc0200000-0xc0600000 4M RW x SHD
0xc0600000-0xc0800000 2M RW NX SHD
0xc0800000-0xc4800000 64M RW NX SHD

Fixes: ded947798469 ("ARM: 8109/1: mm: Modify pte_write and pmd_write logic for LPAE")
Signed-off-by: Philip Derrin <philip@cog.systems>
Tested-by: Neil Dick <neil@cog.systems>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm/mm/dump.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/arm/mm/dump.c
+++ b/arch/arm/mm/dump.c
@@ -126,8 +126,8 @@ static const struct prot_bits section_bi
.val = PMD_SECT_USER,
.set = "USR",
}, {
- .mask = L_PMD_SECT_RDONLY,
- .val = L_PMD_SECT_RDONLY,
+ .mask = L_PMD_SECT_RDONLY | PMD_SECT_AP2,
+ .val = L_PMD_SECT_RDONLY | PMD_SECT_AP2,
.set = "ro",
.clear = "RW",