From: Kees Cook <keescook@chromium.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@amacapital.net>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Andy Lutomirski <luto@kernel.org>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace on i386
Date: Mon, 22 Jul 2019 11:39:03 -0700 [thread overview]
Message-ID: <201907221135.2C2D262D8@keescook> (raw)
In-Reply-To: <alpine.DEB.2.21.1907222027090.1659@nanos.tec.linutronix.de>
On Mon, Jul 22, 2019 at 08:31:32PM +0200, Thomas Gleixner wrote:
> On Mon, 22 Jul 2019, Kees Cook wrote:
> > Just so I'm understanding: the vDSO change introduced code to make an
> > actual syscall on i386, which for most seccomp filters would be rejected?
>
> No. The old x86 specific VDSO implementation had a fallback syscall as
> well, i.e. clock_gettime(). On 32bit clock_gettime() uses the y2038
> endangered timespec.
>
> So when the VDSO was made generic we changed the internal data structures
> to be 2038 safe right away. As a consequence the fallback syscall is not
> clock_gettime(), it's clock_gettime64(). which seems to surprise seccomp.
Okay, it's didn't add a syscall, it just changed it. Results are the
same: conservative filters suddenly start breaking due to the different
call. (And now I see why Andy's alias suggestion would help...)
I'm not sure which direction to do with this. It seems like an alias
list is a large hammer for this case, and a "seccomp-bypass when calling
from vDSO" solution seems too fragile?
--
Kees Cook
next prev parent reply other threads:[~2019-07-22 18:39 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-19 17:03 [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace on i386 Sean Christopherson
2019-07-19 17:40 ` Andy Lutomirski
2019-07-22 17:16 ` Kees Cook
2019-07-22 18:31 ` Thomas Gleixner
2019-07-22 18:39 ` Kees Cook [this message]
2019-07-22 19:17 ` Andy Lutomirski
2019-07-22 23:28 ` Kees Cook
2019-07-22 23:47 ` Andy Lutomirski
2019-07-23 9:18 ` Peter Zijlstra
2019-07-23 14:04 ` Andy Lutomirski
2019-07-23 15:14 ` Peter Zijlstra
2019-07-23 21:55 ` Kees Cook
2019-07-23 22:55 ` Andy Lutomirski
2019-07-23 22:59 ` Thomas Gleixner
2019-07-23 23:43 ` Kees Cook
2019-07-23 23:56 ` Thomas Gleixner
2019-07-26 18:01 ` Sean Christopherson
2019-07-27 17:49 ` Andy Lutomirski
2019-07-27 18:43 ` Thomas Gleixner
2019-07-27 21:52 ` Thomas Gleixner
2019-07-28 0:33 ` Andy Lutomirski
2019-07-28 9:57 ` Arnd Bergmann
2019-07-28 10:30 ` Thomas Gleixner
2019-07-28 15:27 ` Arnd Bergmann
2019-07-28 18:14 ` Thomas Gleixner
2019-07-28 18:16 ` Thomas Gleixner
2019-07-28 11:13 ` Thomas Gleixner
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