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

[Josh Stone]

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@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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