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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Date:	Thu, 19 Jan 2012 16:53:01 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Indan Zupancic <indan@....nu>
Cc:	Jamie Lokier <jamie@...reable.org>,
	Andi Kleen <andi@...stfloor.org>, Martin Mares <mj@....cz>,
	Andi Kleen <ak@...ux.intel.com>,
	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,
	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 Thu, Jan 19, 2012 at 4:21 PM, Indan Zupancic <indan@....nu> wrote:
>
> With current ptrace you can do exactly that. It's just very slow, because
> you have to copy the data word by word via PTRACE_PEEKDATA. But if Linux
> would support something like BSD's PT_IO ptrace request, then it could be
> limited to one extra ptrace command. (PTRACE_STRNCPY would be handy.)

Actually, you could use the new "process_vm_readv/writev()" system
calls. No need to do the crazy slow ptrace stuff.

I dunno. It got merged through Andrew, and the code looks sane, but
I've never actually seen anybody *use* it. So maybe there is something
wrong there. And no, it doesn't have a "strncpy" interface, I'm
afraid.

                   Linus
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