linux-kernel - Re: Compat 32-bit syscall entry from 64-bit task!?

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Message-ID: <20120126110149.GF18613@jl-vm1.vm.bytemark.co.uk>
Date:	Thu, 26 Jan 2012 11:01:49 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Indan Zupancic <indan@....nu>, Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Lutomirski <luto@....edu>,
	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	keescook@...omium.org, john.johansen@...onical.com,
	serge.hallyn@...onical.com, coreyb@...ux.vnet.ibm.com,
	pmoore@...hat.com, eparis@...hat.com, djm@...drot.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, mingo@...e.hu, akpm@...ux-foundation.org,
	khilman@...com, borislav.petkov@....com, amwang@...hat.com,
	ak@...ux.intel.com, eric.dumazet@...il.com, gregkh@...e.de,
	dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com,
	Roland McGrath <mcgrathr@...omium.org>
Subject: Re: Compat 32-bit syscall entry from 64-bit task!?

Denys Vlasenko wrote:
> On Thu, Jan 26, 2012 at 11:31 AM, Jamie Lokier <jamie@...reable.org> wrote:
> > Indan Zupancic wrote:
> >> On Thu, January 26, 2012 02:08, Jamie Lokier wrote:
> >> > Is it disambiguated by PTRACE_EVENT_EXEC happening before the execve
> >> > returns, and you knowing the TID always changes to the PID?  I haven't
> >> > yet checked which TID gets the PTRACE_EVENT_EXEC event, but if it's
> >> > not the old one, perhaps that could be changed.
> >>
> >> Please don't ever change the behaviour of PTRACE_EVENT_EXEC, it's
> >> barely documented already, but if if ever changes it will be also
> >> unreliable.
> >>
> >> It's still unclear if the PTRACE_EVENT_EXEC comes before or after
> >> or instead of the post-execve ptrace event.
> 
> Denis <- confused.
> Was ist das "post-execve ptrace event"? I know no such thing.
> I know about PTRACE_EVENT_EXEC, and "post-execve SIGTRAP".

Sorry, I meant to write execve-syscall-exit event.

> >> I guess before, but
> >> can I count on that? If it is after then I get a stray weird
> >> execve event that messes up the system call cadence.
> >
> > It should be *sent* before because the exec steps must finish before
> > the execve() syscall "returns".
> >
> > I'm not sure if the events are guaranteed to be received in the same
> > order as they are sent.
> 
> All ptrace stops (events and other stops) are synchronous.
> Tracee stops, tracer notices it, tracer restarts tracee,
> and only after this tracee can generate next event.
> Therefore ptrace stops can't get reordered.

That's good to know, thanks.

-- Jamie
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