linux-kernel - Re: [PATCH v4 1/2] ptrace: save the type of syscall-stop in ptrace

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Date:   Thu, 29 Nov 2018 16:03:28 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     "Dmitry V. Levin" <ldv@...linux.org>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Elvira Khabirova <lineprinter@...linux.org>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, strace-devel@...ts.strace.io
Subject: Re: [PATCH v4 1/2] ptrace: save the type of syscall-stop in
 ptrace_message

On 11/28, Andy Lutomirski wrote:
>
> I don't like any of this at all.  Can we please choose a sensible API
> design and let the API drive the implementation instead of vice versa?

I too do not understand your concerns...

>  ISTM the correct solution is to add some new state to task_struct for
> this.

Sure we can do this. I have argued with the previous version not because
the new member blows the task_struct. Although I think it is better to avoid
this if possible.

But this doesn't affect the API.

Yes, this version uses ->ptrace_message but I think this is _good_ exactly
because it is already visible to userspace, so if debugger only needs to
distinguish syscall entry/exit it can simply use PTRACE_GETEVENTMSG without
PTRACE_GET_SYSCALL_INFO.

> If we're concerned about making task_struct bigger, I have a
> half-finished patch to factor all the ptrace tracee state into a
> separate struct.

I even sent the patch(es) which does this several years ago ;)

Oleg.