linux-kernel - Re: [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace on i386

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Message-ID: <20190726180103.GE3188@linux.intel.com>
Date:   Fri, 26 Jul 2019 11:01:03 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Paul Bolle <pebolle@...cali.nl>
Subject: Re: [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace
 on i386

+cc Paul

On Wed, Jul 24, 2019 at 01:56:34AM +0200, Thomas Gleixner wrote:
> On Tue, 23 Jul 2019, Kees Cook wrote:
> 
> > On Wed, Jul 24, 2019 at 12:59:03AM +0200, Thomas Gleixner wrote:
> > > And as we have sys_clock_gettime64() exposed for 32bit anyway you need to
> > > deal with that in seccomp independently of the VDSO. It does not make sense
> > > to treat sys_clock_gettime() differently than sys_clock_gettime64(). They
> > > both expose the same information, but the latter is y2038 safe.
> > 
> > Okay, so combining Andy's ideas on aliasing and "more seccomp flags",
> > we could declare that clock_gettime64() is not filterable on 32-bit at
> > all without the magic SECCOMP_IGNORE_ALIASES flag or something. Then we
> > would alias clock_gettime64 to clock_gettime _before_ the first evaluation
> > (unless SECCOMP_IGNORE_ALIASES is set)?
> > 
> > (When was clock_gettime64() introduced? Is it too long ago to do this
> > "you can't filter it without a special flag" change?)
> 
> clock_gettime64() and the other sys_*time64() syscalls which address the
> y2038 issue were added in 5.1

Paul Bolle pointed out that this regression showed up in v5.3-rc1, not
v5.2.  In Paul's case, systemd-journal is failing.