linux-kernel - Re: [PATCH 2/3] x86: set_personality_ia32() abuses TS

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Message-ID: <20100216171614.GA23503@redhat.com>
Date:	Tue, 16 Feb 2010 18:16:14 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86: set_personality_ia32() abuses TS_COMPAT

On 02/16, Linus Torvalds wrote:
>
> On Tue, 16 Feb 2010, Oleg Nesterov wrote:
> >
> > In fact I'd say this is not right, but fortunetely do_execve() can
> > never return something which could confuse syscall_get_error().
> > And apart from do_signal() we never check TS_COMPAT during return
> > to user-mode.
>
> But 'do_signal()' _can_ happen the first thing after an execve(), no?

this is what I meant,

> And after we have switched to 32-bit mode, we _are_ inside a 32-bit system
> call: the execve has "changed" from a 64-bit one to a 32-bit one.

And this is what I do not understand, we are still in 64-bit execve.

With ot without TS_COMPAT we take the same return path and I can't
see why should we sign-extend ->ax. But I didn't claim this is wrong,
and it is possible I missed something.

> So I really don't understand why you dislike TS_COMPAT here.

The only reason I dislike TS_COMPAT is that I spent a lot of time
trying to understand the necessity to set it here when I tried to
understand the basics of compat issues.

> I understand not liking TS_COMPAT in the first place (it would be nice to
> not have that flag at all), but considering that it exists, and it is
> supposed to be set while in 32-bit system calls, setting it on a 32-bit
> execve() seems to be the RightThing(tm) to do.

OK, please ignore the patch then.

As I said, only the first patch probably makes sense, and even it
was not tested.

Cough. And since I already made a lot of noise...

Now that we always call setup_new_exec() which does
arch_pick_mmap_layout(), what is the point of
exec_mmap()->arch_pick_mmap_layout() ?

Oleg.

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