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 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
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-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org 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@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", #elif __LINUX_ARM_ARCH__ >= 6
Patches currently in stable-queue which might be from philip@cog.systems are
queue-3.18/arm-8721-1-mm-dump-check-hardware-ro-bit-for-lpae.patch