linux-kernel - Re: a method to distinguish between syscall-enter/exit-stop

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Date:	Sat, 7 Feb 2015 02:17:20 +0300
From:	"Dmitry V. Levin" <ldv@...linux.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Will Drewry <wad@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	Alexei Starovoitov <ast@...mgrid.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>
Subject: Re: a method to distinguish between syscall-enter/exit-stop

On Fri, Feb 06, 2015 at 12:07:03PM -0800, Kees Cook wrote:
> On Fri, Feb 6, 2015 at 11:32 AM, Andy Lutomirski <luto@...capital.net> wrote:
> > On Fri, Feb 6, 2015 at 11:23 AM, Kees Cook <keescook@...omium.org> wrote:
[...]
> >> And an unrelated thought:
> >>
> >> 3) Can't we find some way to fix the inability of a ptracer to
> >> distinguish between syscall-enter-stop and syscall-exit-stop?
> >
> > Couldn't we add PTRACE_O_TRACESYSENTRY and PTRACE_O_TRACESYSEXIT along
> > the lines of PTRACE_O_TRACESYSGOOD?
> 
> That might be a nice idea. I haven't written a test to see, but what
> does PTRACE_GETEVENTMSG return on syscall-enter/exit-stop?

The value returned by PTRACE_GETEVENTMSG is the value set along with the
latest PTRACE_EVENT_*.
In case of syscall-enter/exit-stop (which is not a PTRACE_EVENT_*),
there is no particular value set for PTRACE_GETEVENTMSG.


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