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

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Message-Id: <201201260221.33224.vda.linux@googlemail.com>
Date:	Thu, 26 Jan 2012 02:21:33 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Jamie Lokier <jamie@...reable.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Indan Zupancic <indan@....nu>,
	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!?

On Thursday 26 January 2012 01:59, Jamie Lokier wrote:
> Denys Vlasenko wrote:
> > (2) syscall exit compat-ness is known from entry type - no need to indicate it; and
> > (3) if we would flag syscall entry with an event value in wait status, then syscall
> > exit will be already distinquisable.
> >
> > Thus, minimally we need one new option, PTRACE_O_TRACE_SYSENTRY -
> > "on syscall entry ptrace stop, set a nonzero event value in wait status"
> > , and two event values: PTRACE_EVENT_SYSCALL_ENTRY (for native entry),
> > PTRACE_EVENT_SYSCALL_ENTRY1 for compat one.
> 
> PTRACE_EVENT_SYSCALL_EXIT would cleanly indicate that the new option
> is actually working without the tracer needing to do a fork+test, if
> PTRACE_ATTACH is used and for some reason the tracer sees a syscall
> exit first.

Can't happen. After PTRACE_ATTACH, you can only see tracee dying, or
getting a signal delivery (usually a SIGSTOP). Anything else
would be a kernel bug.

-- 
vda
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