This is a note to let you know that I've just added the patch titled
ARM: 8721/1: mm: dump: check hardware RO bit for LPAE
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm-8721-1-mm-dump-check-hardware-ro-bit-for-lpae.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 3b0c0c922ff4be275a8beb87ce5657d16f355b54 Mon Sep 17 00:00:00 2001
From: Philip Derrin <philip@cog.systems>
Date: Tue, 14 Nov 2017 00:55:26 +0100
Subject: ARM: 8721/1: mm: dump: check hardware RO bit for LPAE
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@xxxxxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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",
#elif __LINUX_ARM_ARCH__ >= 6
Patches currently in stable-queue which might be from philip@cog.systems are
queue-4.9/arm-8722-1-mm-make-strict_kernel_rwx-effective-for-lpae.patch
queue-4.9/arm-8721-1-mm-dump-check-hardware-ro-bit-for-lpae.patch