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

Josh Stone
2015-06-03T20:07:44Z

On 06/03/2015 05:09 AM, Greg Kroah-Hartman wrote:
> 4.0-stable review patch. If anyone has any objections, please let me know.

I sent a copycat patch for arm64, but I think it may be a problem to
leave interrupts disabled for __sys_trace_return. Thoughts, Russell?

> ------------------
>
> From: Russell King <rmk+kernel@arm.linux.org.uk>
>
> 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@redhat.com>
> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> ---
> 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
>
>