[PATCH 4.9 064/128] ARM: 8978/1: mm: make act_mm() respect THREAD_SIZE

Greg Kroah-Hartman
2020-06-19T14:43:44Z

From: Linus Walleij <linus.walleij@linaro.org>

[ Upstream commit e1de94380af588bdf6ad6f0cc1f75004c35bc096 ]

Recent work with KASan exposed the folling hard-coded bitmask
in arch/arm/mm/proc-macros.S:

bic rd, sp, #8128
bic rd, rd, #63

This forms the bitmask 0x1FFF that is coinciding with
(PAGE_SIZE << THREAD_SIZE_ORDER) - 1, this code was assuming
that THREAD_SIZE is always 8K (8192).

As KASan was increasing THREAD_SIZE_ORDER to 2, I ran into
this bug.

Fix it by this little oneline suggested by Ard:

bic rd, sp, #(THREAD_SIZE - 1) & ~63

Where THREAD_SIZE is defined using THREAD_SIZE_ORDER.

We have to also include <linux/const.h> since the THREAD_SIZE
expands to use the _AC() macro.

Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm/mm/proc-macros.S | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
index f8bb65032b79..796e8f675a93 100644
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S
@@ -4,6 +4,7 @@
* VMA_VM_FLAGS
* VM_EXEC
*/
+#include <linux/const.h>
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>

@@ -34,7 +35,7 @@
* act_mm - get current->active_mm
*/
.macro act_mm, rd
- bic \rd, sp, #8128
+ bic \rd, sp, #(THREAD_SIZE - 1) & ~63
bic \rd, \rd, #63
ldr \rd, [\rd, #TI_TASK]
ldr \rd, [\rd, #TSK_ACTIVE_MM]
--
2.25.1