Messages in this thread | | | Subject | Re: [PATCH v2 5/5] x86/pti: Do not enable PTI on fixed Intel processors | From | David Woodhouse <> | Date | Wed, 24 Jan 2018 18:59:21 +0000 |
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On Wed, 2018-01-24 at 18:40 +0000, Alan Cox wrote: > Nobody has published official statements on Cyrix or AMD 32bit processors > so we don't know if they are vulnerable to meltdown. One problem I > suspect is that as with things like Alpha 21264 - the people who knew are > probably long retired. We do know the Intel ones I listed are OK and the > Centaur. > > If someone can figure out the Cyrix and AMD cases that would be great.
Well Tom already submitted a patch to turn it off for *all* AMD, 32-bit and 64-bit.
> > > > By the time the dust settles we might end up with a bunch of different > > match tables, *one* of which is "does not speculate at all". And the > > conditions for the different bugs will each use different sets of match > > tables. For example > > > > if (!x86_match_cpu(cpu_no_speculation_at_all) && > > !x86_match_cpu(speculation_but_no_meltdown) && > > !cpu_sets_rdcl_no()) > > setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN); > > > > if (!x86_match_cpu(cpu_no_speculation_at_all) && > > !x86_match_cpu(no_branch_target_buffer)) > > setup_force_cpu_bug(X86_BUG_SPECTRE_V2); > There are afaik no x86 processors that speculate and don't have a BTB. > It's a bit like building a racing car with no gearbox.
Right, "has a BTB and doesn't tag/flush it according to privilege level and context". Which is the thing that, as lamented, Intel hasn't even proposed a way to *tell* us that's the case, if/when they finally manage to fix it up in the next generation *after* the IBRS_ALL hack.
So yeah, X86_BUG_SPECTRE_V2 probably *does* end up being "speculates".
I'll change !Meltdown from ANY,5 to INTEL,5 + CENTAUR,5 as you suggest, and we can work on Spectre separately.
Thanks. [unhandled content-type:application/x-pkcs7-signature] | |