[PATCH AUTOSEL 4.4 09/37] ARM: 8978/1: mm: make act_mm() respect THREAD_SIZE

[Sasha Levin]

From: Linus Walleij <linus.walleij@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Cc: Florian Fainelli <f.fainelli@xxxxxxxxx>
Suggested-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 e6bfdcc381f8..1da55d34f4d6 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>
 
@@ -30,7 +31,7 @@
  * 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