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Date:   Fri, 14 Sep 2018 15:09:27 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Florian Weimer <fweimer@redhat.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@kernel.org>, x86@kernel.org,
        Matt Rickard <matt@softrans.com.au>,
        Stephen Boyd <sboyd@kernel.org>,
        John Stultz <john.stultz@linaro.org>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        devel@linuxdriverproject.org,
        virtualization@lists.linux-foundation.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>, Juergen Gross <jgross@suse.com>
Subject: Re: [patch 00/11] x86/vdso: Cleanups, simmplifications and CLOCK_TAI
 support
Message-ID: <20180914130927.GK24124@hirez.programming.kicks-ass.net>
References: <20180914125006.349747096@linutronix.de>
 <2f723b28-8f81-4b02-861c-42f756a8825a@redhat.com>
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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.