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>

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index f8ccc21fa032354facead9735abf9f4eb0cb7eb2..4e7f40c577e6e4fe9df3dd677b0d146b1ceb13c2 100644 (file)
--- 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