ARM: Prepare for randomized task_struct

With the new task struct randomization, we can run into a build
failure for certain random seeds, which will place fields beyond
the allow immediate size in the assembly:

arch/arm/kernel/entry-armv.S: Assembler messages:
arch/arm/kernel/entry-armv.S:803: Error: bad immediate value for offset (4096)

Only two constants in asm-offset.h are affected, and I'm changing
both of them here to work correctly in all configurations.

One more macro has the problem, but is currently unused, so this
removes it instead of adding complexity.

Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[kees: Adjust commit log slightly]
Signed-off-by: Kees Cook <keescook@chromium.org>

3 files changed, 10 insertions, 7 deletions

diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 68b06f9c65de..ad301f107dd2 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -87,6 +87,8 @@
 #define CALGN(code...)
 #endif
 
+#define IMM12_MASK 0xfff
+
 /*
  * Enable and disable interrupts
  */
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 9f157e7c51e7..c731f0d2b2af 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -797,7 +797,10 @@ ENTRY(__switch_to)
 #if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
         ldr     r7, [r2, #TI_TASK]
         ldr     r8, =__stack_chk_guard
-        ldr     r7, [r7, #TSK_STACK_CANARY]
+        .if (TSK_STACK_CANARY > IMM12_MASK)
+        add     r7, r7, #TSK_STACK_CANARY & ~IMM12_MASK
+        .endif
+        ldr     r7, [r7, #TSK_STACK_CANARY & IMM12_MASK]
 #endif
 #ifdef CONFIG_CPU_USE_DOMAINS
         mcr     p15, 0, r6, c3, c0, 0           @ Set domain register
diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
index 0d40c285bd86..f944836da8a2 100644
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S
@@ -25,11 +25,6 @@
         ldr     \rd, [\rn, #VMA_VM_FLAGS]
         .endm
 
-        .macro  tsk_mm, rd, rn
-        ldr     \rd, [\rn, #TI_TASK]
-        ldr     \rd, [\rd, #TSK_ACTIVE_MM]
-        .endm
-
 /*
  * act_mm - get current->active_mm
  */
@@ -37,7 +32,10 @@
         bic     \rd, sp, #8128
         bic     \rd, \rd, #63
         ldr     \rd, [\rd, #TI_TASK]
-        ldr     \rd, [\rd, #TSK_ACTIVE_MM]
+        .if (TSK_ACTIVE_MM > IMM12_MASK)
+        add     \rd, \rd, #TSK_ACTIVE_MM & ~IMM12_MASK
+        .endif
+        ldr     \rd, [\rd, #TSK_ACTIVE_MM & IMM12_MASK]
         .endm
 
 /*