From: Andi Kleen <ak@muc.de>
To: Arne Georg Gleditsch <arne.gleditsch@dolphinics.no>
Cc: linux-kernel@vger.kernel.org, John Stultz <johnstul@us.ibm.com>,
Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
Roman Zippel <zippel@linux-m68k.org>
Subject: Re: arch/x86/kernel/vsyscall_64.c: overeager NOP of syscalls
Date: 21 Feb 2008 16:58:52 +0100
Date: Thu, 21 Feb 2008 16:58:52 +0100 [thread overview]
Message-ID: <20080221155852.GA42442@muc.de> (raw)
In-Reply-To: <kjm4pc3d92p.fsf@pelargir.dolphinics.no>
On Wed, Feb 20, 2008 at 02:57:34PM +0100, Arne Georg Gleditsch wrote:
> Hi,
>
> I'm looking at 2.6.25-rc2. vsyscall_sysctl_change contains code to NOP
> out the actual system call instructions of the vsyscall page when
> vsyscall64 is enabled. This seems to interact badly with the fallback
> code in do_vgettimeofday which tries to call gettimeofday if the
> configured clock source does not support vread. (In effect,
> gettimeofday() becomes a nop and time() always returns 0. Not very
> useful.)
>
> Is there a good reason to keep this? Aren't the instructions in
> question avoided (or invoked) according to the vsyscall64 flag by the
> surrounding logic anyway?
Yes they are. But a system call sequence at a known fixed address
is potentially useful to exploits. That is why it is nop'ed out when
it is not needed.
-Andi
next prev parent reply other threads:[~2008-02-21 16:02 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-20 13:57 arch/x86/kernel/vsyscall_64.c: overeager NOP of syscalls Arne Georg Gleditsch
2008-02-20 18:08 ` Thomas Gleixner
2008-02-21 15:58 ` Andi Kleen [this message]
2008-02-21 19:45 ` Thomas Gleixner
2008-02-21 20:02 ` john stultz
2008-02-21 20:47 ` Thomas Gleixner
2008-02-21 20:59 ` Thomas Gleixner
2008-02-22 12:55 ` Andi Kleen
2008-02-22 12:49 ` Andi Kleen
2008-02-22 10:38 ` Arne Georg Gleditsch
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