linux-kernel - Re: [PATCH v2 4/6] powerpc: use common ptrace_syscall_enter hook to handle _TIF_SYSCALL

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Date:   Mon, 18 Mar 2019 17:26:18 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Oleg Nesterov <oleg@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Richard Weinberger <richard@....at>, jdike@...toit.com,
        Steve Capper <Steve.Capper@....com>,
        Haibo Xu <haibo.xu@....com>, Bin Lu <bin.lu@....com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2 4/6] powerpc: use common ptrace_syscall_enter hook to
 handle _TIF_SYSCALL_EMU

On Mon, Mar 18, 2019 at 10:49:23AM +0000, Sudeep Holla wrote:
> Now that we have a new hook ptrace_syscall_enter that can be called from
> syscall entry code and it handles PTRACE_SYSEMU in generic code, we
> can do some cleanup using the same in do_syscall_trace_enter.
> 
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  arch/powerpc/kernel/ptrace.c | 48 ++++++++++++++++--------------------
>  1 file changed, 21 insertions(+), 27 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index 2e2183b800a8..05579a5dcb12 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -3278,35 +3278,29 @@ long do_syscall_trace_enter(struct pt_regs *regs)
>  
>  	user_exit();
>  
> -	flags = READ_ONCE(current_thread_info()->flags) &
> -		(_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
> -
> -	if (flags) {
> -		int rc = tracehook_report_syscall_entry(regs);
> +	if (unlikely(ptrace_syscall_enter(regs))) {
> +		/*
> +		 * A nonzero return code from tracehook_report_syscall_entry()
> +		 * tells us to prevent the syscall execution, but we are not
> +		 * going to execute it anyway.
> +		 *
> +		 * Returning -1 will skip the syscall execution. We want to
> +		 * avoid clobbering any registers, so we don't goto the skip
> +		 * label below.
> +		 */
> +		return -1;
> +	}

This comment is out of sync with the changed code.


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