ARM: 7912/1: check stack pointer in get_wchan

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
Link: http://stackoverflow.com/questions/18479894/unwind-frame-cause-a-kernel-paging-error
Cc: <stable@vger.kernel.org>
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>

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 94f6b05..92f7b15 100644 (file)
--- 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;