Re: [patch added to the 3.12 stable tree] x86_64, switch_to(): Load TLS descriptors before switching DS and ES

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> > > It even has a CVE (CVE-2014-9419).

Every fart can get a CVE these days.

> attack may only work against 32-bit targets.  Maybe we should just get
> rid of the fsbase/gsbase-via-GDT optimization.  (If we did that, then
> we could go farther and turn TLS off entirely on non-compat kernels.)

Sorry, but this is just crazy talk. Just don't go there.

> 
> Andi, I think the 64-bit TLS code.  Do you recall what the <4GB
> optimization is for?

To avoid the WRMSR penalty on the context switch.

It is obsolete with the WR*BASE patchkit.

> Hmm.  On my system, both PIE and non-PIE 64-bit executables seem to
> put their TLS base in mmap space, which is far above 4GB.  So this

Yes some recent systems have broken the optimization.  But it still
helps in a lot of cases.

> > I indeed can run estest with failures on 3.12. But what does it mean to
> > me would be nice to have explained...

AFAIK it means nothing.

-Andi
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