linux-kernel - Re: [PATCH v5 9/9] x86-64: Add CONFIG_UNSAFE

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Date:	Mon, 06 Jun 2011 23:53:09 +0200
From:	pageexec@...email.hu
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Andi Kleen <andi@...stfloor.org>, Andy Lutomirski <luto@....edu>,
	Ingo Molnar <mingo@...e.hu>, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Jesper Juhl <jj@...osbits.net>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Jan Beulich <JBeulich@...ell.com>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	Brian Gerst <brgerst@...il.com>,
	Louis Rilling <Louis.Rilling@...labs.com>,
	Valdis.Kletnieks@...edu
Subject: Re: [PATCH v5 9/9] x86-64: Add CONFIG_UNSAFE_VSYSCALLS to feature-removal-schedule

On 7 Jun 2011 at 5:40, Linus Torvalds wrote:

> On Tue, Jun 7, 2011 at 3:46 AM,  <pageexec@...email.hu> wrote:
> >
> >> I'm happy with perhaps moving away from the fixed-address vdso,
> >
> > it's not about the vdso that has been mmap'ed and randomized for quite some
> > time now. it's about the amd64 specific vsyscall page.
> 
> Duh. What do you think that thing is? It's a special fixed-address
> vdso.

that we call the vsyscall page and not some random vdso thing, they're quite
different, that's why there's this whole patch series, duh.

> What I complain about in the patch series was (specifically) that I
> think the naming sucks and (non-specifically) that the whole series is
> annoying.
> 
> The config name is misleading and pointlessly scary - the whole thing
> is not in itself "unsafe", so calling it that is just wrong.

if it's safe to have the vsyscall page at a fixed address, then you surely
wouldn't object to have its replacement at a fixed address as well, would
you? yes/no? (if it's a 'yes' then you'd better have some non-security
arguments too ;)

> We *definitely* don't want to name it in a way that makes some random
> person just turn it off because it's scary, since the random person
> *shouldn't* turn it off today. Comprende?

actually you confused yourself and got it backwards. we want everyone sane
who cares an iota about security to turn off the legacy/fixed address vsyscall
as soon as possible else it's a pointless exercise. capito?

> If we can replace the vsyscall page with a page fault or int3 or
> whatever, and it's only used for the 'time()' system call, just do it. 

i agree fully, there's no real reason for a config option imho, i never
had one in PaX and noone ever complained let alone noticed it (except
perhaps for failed exploit attempts but that's by design).

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