[PATCH 4.0 108/148] ARM: fix missing syscall trace exit

From: Greg Kroah-Hartman
Date: Wed Jun 03 2015 - 08:39:41 EST


4.0-stable review patch. If anyone has any objections, please let me know.

------------------

From: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>

commit 1b97937246d8b97c0760d16d8992c7937bdf5e6a upstream.

Josh Stone reports:

I've discovered a case where both arm and arm64 will miss a ptrace
syscall-exit that they should report. If the syscall is entered
without TIF_SYSCALL_TRACE set, then it goes on the fast path. It's
then possible to have TIF_SYSCALL_TRACE added in the middle of the
syscall, but ret_fast_syscall doesn't check this flag again.

Fix this by always checking for a syscall trace in the fast exit path.

Reported-by: Josh Stone <jistone@xxxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
arch/arm/kernel/entry-common.S | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -33,7 +33,9 @@ ret_fast_syscall:
UNWIND(.fnstart )
UNWIND(.cantunwind )
disable_irq @ disable interrupts
- ldr r1, [tsk, #TI_FLAGS]
+ ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing
+ tst r1, #_TIF_SYSCALL_WORK
+ bne __sys_trace_return
tst r1, #_TIF_WORK_MASK
bne fast_work_pending
asm_trace_hardirqs_on


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