ARM: 6654/1: perf/oprofile: fix off-by-one in stack check

Since tail is the previous fp - 1, we need to compare the new fp with tail + 1
to ensure that we don't end up passing in the same tail again, in order to
avoid a potential infinite loop in the perf interrupt handler (which has been
observed to occur).  A similar fix seems to be needed in the OProfile code.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index 5efa2647a2fb..d150ad1ccb5d 100644
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -700,7 +700,7 @@ user_backtrace(struct frame_tail __user *tail,
          * Frame pointers should strictly progress back up the stack
          * (towards higher addresses).
          */
-        if (tail >= buftail.fp)
+        if (tail + 1 >= buftail.fp)
                 return NULL;
 
         return buftail.fp - 1;