ARM: 8978/1: mm: make act_mm() respect THREAD_SIZE

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 <[email protected]> Cc: Florian Fainelli <[email protected]> Suggested-by: Ard Biesheuvel <[email protected]> Signed-off-by: Linus Walleij <[email protected]> Signed-off-by: Russell King <[email protected]>
hardkernel · May 26, 2020 · e1de943 · e1de943
1 parent fce2bc2
commit e1de943
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
@@ -5,6 +5,7 @@
  *  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]
 	.if (TSK_ACTIVE_MM > IMM12_MASK)