linux-kernel - Re: [PATCH v4 0/6] Micro-optimize vclock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 17 May 2011 07:11:06 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Borislav Petkov <bp@...64.org>
Subject: Re: [PATCH v4 0/6] Micro-optimize vclock_gettime

On Tue, May 17, 2011 at 4:00 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Thomas Gleixner <tglx@...utronix.de> wrote:
>
>> > see if I can persuade Uli to take accept a glibc patch to stop calling it
>> > in future static glibc versions.
>>
>> How wide spread is this in reality on 64bit systems ?
>>
>> IOW, what's the damage if we take a trap and emulate it in the most painful
>> way we can come up with ?

I dunno.  I'll measure it.

>
> Well, how does that differ from having the real syscall instruction there? How
> are we going to filter real (old-)glibc calls from exploits?

Because there are only four vsyscalls: vgettimeofday, vtime, vgetcpu,
and venosys.  None of them have side-effects, so they only allow an
attacker to write something to user memory somewhere.  The
implementation of vgettimeofday needs a syscall instruction internally
for its fallback, which means that an attack could jump there instead
of to the start of the vsyscall implementation.

>
> If it can be filtered in a meaningful way then we should just do that and
> perhaps offer a (default enabled) .config COMPAT_VDSO_EMU=y switch to turn the
> emulation off.
>
> That way we keep the ABI and also have a way out for users who *really* need
> this to work in a performant way.

Yeah, that probably makes more sense.  It'll make for an uglier
diffstat, though -- there's a lot of ugly duplicate code around to
make vgettimeofday and vgetcpu work.

--Andy

>
> Thanks,
>
>        Ingo
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/