ARM: fix missing syscall trace exit

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@redhat.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index f8ccc21fa032..4e7f40c577e6 100644
--- 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