[PATCH 3.2 127/185] ARM: 7912/1: check stack pointer in get_wchan

Ben Hutchings
2013-12-29T02:47:35Z

From: Konstantin Khlebnikov <k.khlebnikov@samsung.com>

commit 1b15ec7a7427d4188ba91b9bbac696250a059d22 upstream.

get_wchan() is lockless. Task may wakeup at any time and change its own stack,
thus each next stack frame may be overwritten and filled with random stuff.

/proc/$pid/stack interface had been disabled for non-current tasks, see [1]
But 'wchan' still allows to trigger stack frame unwinding on volatile stack.

This patch fixes oops in unwind_frame() by adding stack pointer validation on
each step (as x86 code do), unwind_frame() already checks frame pointer.

Also I've found another report of this oops on stackoverflow (irony).

Link: http://www.spinics.net/lists/arm-kernel/msg110589.html [1]
Link: http://stackoverflow.com/questions/18479894/unwind-frame-cause-a-kernel-paging-error

Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@samsung.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/arm/kernel/process.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -468,6 +468,7 @@ EXPORT_SYMBOL(kernel_thread);
unsigned long get_wchan(struct task_struct *p)
{
struct stackframe frame;
+ unsigned long stack_page;
int count = 0;
if (!p || p == current || p->state == TASK_RUNNING)
return 0;
@@ -476,9 +477,11 @@ unsigned long get_wchan(struct task_stru
frame.sp = thread_saved_sp(p);
frame.lr = 0; /* recovered from the stack */
frame.pc = thread_saved_pc(p);
+ stack_page = (unsigned long)task_stack_page(p);
do {
- int ret = unwind_frame(&frame);
- if (ret < 0)
+ if (frame.sp < stack_page ||
+ frame.sp >= stack_page + THREAD_SIZE ||
+ unwind_frame(&frame) < 0)
return 0;
if (!in_sched_functions(frame.pc))
return frame.pc;