linux-kernel - [PATCH] ARM: fix randomized task

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Date:   Fri, 30 Jun 2017 17:34:43 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     kernel-hardening@...ts.openwall.com,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] ARM: fix randomized task_struct

With the new task struct randomization, we can run into a build
failure for certain random seeds:

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@...aro.org>
Fixes: c33d8b12fbbd ("task_struct: Allow randomized layout")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/arm/kernel/entry-armv.S |  5 ++++-
 arch/arm/mm/proc-macros.S    | 10 ++++------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 9f157e7c51e7..db6d22b23bd8 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 > PAGE_MASK)
+	add	r7, r7, #TSK_STACK_CANARY & PAGE_MASK
+	.endif
+	ldr	r7, [r7, #TSK_STACK_CANARY & ~PAGE_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..2c5f2a0a708b 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 > PAGE_MASK)
+	add	\rd, \rd, #TSK_ACTIVE_MM & PAGE_MASK
+	.endif
+	ldr	\rd, [\rd, #TSK_ACTIVE_MM & ~PAGE_MASK]
 	.endm
 
 /*
-- 
2.9.0