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

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Message-ID: <201907231636.AD3ED717D@keescook>
Date:   Tue, 23 Jul 2019 16:43:04 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace
 on i386

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?)

-- 
Kees Cook