linux-kernel - Re: [patch 00/11] x86/vdso: Cleanups, simmplifications and CLOCK

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Date:   Fri, 14 Sep 2018 15:09:27 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Matt Rickard <matt@...trans.com.au>,
        Stephen Boyd <sboyd@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        devel@...uxdriverproject.org,
        virtualization@...ts.linux-foundation.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Juergen Gross <jgross@...e.com>
Subject: Re: [patch 00/11] x86/vdso: Cleanups, simmplifications and CLOCK_TAI
 support

On Fri, Sep 14, 2018 at 02:56:46PM +0200, Florian Weimer wrote:
> On 09/14/2018 02:50 PM, Thomas Gleixner wrote:
> > Matt attempted to add CLOCK_TAI support to the VDSO clock_gettime()
> > implementation, which extended the clockid switch case and added yet
> > another slightly different copy of the same code.
> > 
> > Especially the extended switch case is problematic as the compiler tends to
> > generate a jump table which then requires to use retpolines.
> 
> Does vDSO code really have to use retpolines?  It's in userspace, after all.

Userspace is equally susceptible to spectre-v2. Ideally we'd recompile
world with retpoline, but given the amount of inline asm in say things
like openssl and similar projects, validating that there are indeed no
indirect calls/jumps left is nontrivial.

There are currently pending patches to otherwise address user-user
spectre-v2 attacks.