Re: [patch 00/11] x86/vdso: Cleanups, simmplifications and CLOCK_TAI support

From: Peter Zijlstra
Date: Fri Sep 14 2018 - 09:09:53 EST

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.