linux-kernel - Re: Compat 32-bit syscall entry from 64-bit task!? [was: Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]

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Message-ID: <CA+55aFyVTh4SQjjcf3x9BSzULttNVcmG9FyaKzhok=2_804xWA@mail.gmail.com>
Date:	Tue, 17 Jan 2012 18:27:19 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jamie Lokier <jamie@...reable.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Indan Zupancic <indan@....nu>,
	Andrew Lutomirski <luto@....edu>,
	Oleg Nesterov <oleg@...hat.com>,
	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!? [was: Re:
 [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]

On Tue, Jan 17, 2012 at 6:04 PM, Jamie Lokier <jamie@...reable.org> wrote:
>
> I think Indan means code is running with 64-bit cs, but the kernel
> treats int $0x80 as a 32-bit syscall and sysenter as a 64-bit syscall,
> and there's no way for the ptracer to know which syscall the kernel
> will perform, even by looking at all registers.  It looks like a hole
> in ptrace which could be fixed.

We could possibly munge the "orig_ax" field to be different for the
int80 vs syscall cases. That's really the only field that isn't direct
x86 state. And it's 64 bits wide, but we really only care about the
low 32 bits in the kernel. So a bit in the high bits that says "this
was a int80 entry" would be possible.

                       Linus
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