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SubjectRe: [PATCH] arm: check stack pointer in get_wchan
On Fri, Nov 15, 2013 at 12:19:07PM +0000, Konstantin Khlebnikov wrote:
> 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).

For that comment alone:

Acked-by: Will Deacon <will.deacon@arm.com>

[also, the patch looks sane to me].

Will

> Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@samsung.com>
> Cc: Vyacheslav Tyrtov <v.tyrtov@samsung.com>
> Link: http://www.spinics.net/lists/arm-kernel/msg110589.html [1]
> Link: http://stackoverflow.com/questions/18479894/unwind-frame-cause-a-kernel-paging-error
> ---
> arch/arm/kernel/process.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
> index 94f6b05..92f7b15 100644
> --- a/arch/arm/kernel/process.c
> +++ b/arch/arm/kernel/process.c
> @@ -404,6 +404,7 @@ EXPORT_SYMBOL(dump_fpu);
> 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;
> @@ -412,9 +413,11 @@ unsigned long get_wchan(struct task_struct *p)
> 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;
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>


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