linux-kernel - Re: [RFC PATCH RESEND v3 3/3] ptrace: add PTRACE_EVENT_SECCOMP support to PTRACE_GET_SYSCALL

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Date:   Tue, 27 Nov 2018 06:21:09 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Elvira Khabirova <lineprinter@...linux.org>,
        Oleg Nesterov <oleg@...hat.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Eugene Syromyatnikov <esyr@...hat.com>,
        linux-kernel@...r.kernel.org, strace-devel@...ts.strace.io,
        linux-api@...r.kernel.org
Subject: Re: [RFC PATCH RESEND v3 3/3] ptrace: add PTRACE_EVENT_SECCOMP
 support to PTRACE_GET_SYSCALL_INFO

On Tue, Nov 27, 2018 at 04:07:32AM +0100, Elvira Khabirova wrote:
> On Mon, 26 Nov 2018 15:35:24 +0100, Oleg Nesterov wrote:
> > On 11/25, Elvira Khabirova wrote:
> > >
> > > Extend PTRACE_GET_SYSCALL_INFO to support PTRACE_EVENT_SECCOMP stops.
> > > The information returned is the same as for syscall-enter-stops.  
> > 
> > Oh, this is not nice ;) there must be a better option, I hope... Plus
> > 
> > Can't ptrace_get_syscall() check
> > 
> > 	child->exit_code == (PTRACE_EVENT_SECCOMP << 8) | SIGTRAP;
> > 
> > to detect the PTRACE_EVENT_SECCOMP case?
> 
> Nope; looks like exit_code is zeroed after wait().

It's explicitly reset to zero in wait_task_stopped() unless WNOWAIT wait
option is set.  When strace requests PTRACE_GET_SYSCALL_INFO after
wait4(), child->exit_code is already set to zero.


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