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authorNicolas Pitre <nico@fluxnic.net>2010-06-07 21:50:33 -0400
committerNicolas Pitre <nico@fluxnic.net>2010-06-14 21:31:01 -0400
commitdf0698be14c6683606d5df2d83e3ae40f85ed0d9 (patch)
treefa0a2c08509d88e74d7033fa922f1cdfef83290f /arch/arm/kernel/entry-armv.S
parentc743f38013aeff58ef6252601e397b5ba281c633 (diff)
downloadlinux-linaro-stable-df0698be14c6683606d5df2d83e3ae40f85ed0d9.tar.gz
ARM: stack protector: change the canary value per task
A new random value for the canary is stored in the task struct whenever a new task is forked. This is meant to allow for different canary values per task. On ARM, GCC expects the canary value to be found in a global variable called __stack_chk_guard. So this variable has to be updated with the value stored in the task struct whenever a task switch occurs. Because the variable GCC expects is global, this cannot work on SMP unfortunately. So, on SMP, the same initial canary value is kept throughout, making this feature a bit less effective although it is still useful. One way to overcome this GCC limitation would be to locate the __stack_chk_guard variable into a memory page of its own for each CPU, and then use TLB locking to have each CPU see its own page at the same virtual address for each of them. Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Diffstat (limited to 'arch/arm/kernel/entry-armv.S')
-rw-r--r--arch/arm/kernel/entry-armv.S8
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 7ee48e7f8f31..2d14081b26b1 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -745,6 +745,11 @@ ENTRY(__switch_to)
mov r4, #0xffff0fff
str r3, [r4, #-15] @ TLS val at 0xffff0ff0
#endif
+#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
+ ldr r7, [r2, #TI_TASK]
+ ldr r8, =__stack_chk_guard
+ ldr r7, [r7, #TSK_STACK_CANARY]
+#endif
#ifdef CONFIG_MMU
mcr p15, 0, r6, c3, c0, 0 @ Set domain register
#endif
@@ -753,6 +758,9 @@ ENTRY(__switch_to)
ldr r0, =thread_notify_head
mov r1, #THREAD_NOTIFY_SWITCH
bl atomic_notifier_call_chain
+#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
+ str r7, [r8]
+#endif
THUMB( mov ip, r4 )
mov r0, r5
ARM( ldmia r4, {r4 - sl, fp, sp, pc} ) @ Load all regs saved previously