linux-kernel - Re: PTRACE_SYSCALL && vsyscall (Was: arch_check_bp_in

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Date:	Wed, 9 Jan 2013 18:52:03 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pedro Alves <palves@...hat.com>
Cc:	u3557@...o.sublimeip.com, Denys Vlasenko <dvlasenk@...hat.com>,
	Jan Kratochvil <jan.kratochvil@...hat.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: PTRACE_SYSCALL && vsyscall (Was: arch_check_bp_in_kernelspace:
	fix the range check)

On 01/08, Pedro Alves wrote:
>
> On 12/04/2012 05:59 PM, Oleg Nesterov wrote:
>
> > But If we want to allow to trace vsyscall's, hw bp doesn't look very
> > nice imo. HBP_NUM = 4 and you need to setup 3 bp's to trace them all.
>
> Irrespective of the whole syscall tracing issue, allowing HW bkpts in
> the vsyscall just seems like a bug fix to me.

And I never argued. I sent the patch iirc ;)

> > That is why I think PTRACE_SYSCALL should "simply work" somehow. And
> > so far I think that "just report syscall_exit with orig_ax = -1" is
> > the best (and simple) solution.
>
> If you report exit alone, you'll confuse current GDB into mistaking
> it for an enter,

Sure. That is why I asked Jan.

> > OK. We can do more. We can report both syscall_enter/exit and we can
> > change orig_ax/ax temporary to "fool" the tracer, so that everything
> > will look as a "normal" syscall. Like vsyscall_seccomp() does.
> >
> > But this needs much more changes.
>
> I'd just like to add, that if any new syscall related option is
> to be added, can we please just go all the way and add
> PTRACE_EVENT_SYSCALL_ENTER|PTRACE_EVENT_SYSCALL_EXIT instead?

Oh yes, this was suggested many times.

Oleg.

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