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Re: [PATCH 0/5] x86: CVE-2017-5715, aka Spectre
On Wed, Jan 10, 2018 at 05:13:36PM -0700, Jeff Law wrote:
> On 01/08/2018 07:23 AM, Alan Modra wrote:
> > On Sun, Jan 07, 2018 at 04:36:20PM -0700, Jeff Law wrote:
> >> On 01/07/2018 03:58 PM, H.J. Lu wrote:
> >>> This set of patches for GCC 8 mitigates variant #2 of the speculative execution
> >>> vulnerabilities on x86 processors identified by CVE-2017-5715, aka Spectre.
> > [snip]
> >> My fundamental problem with this patchkit is that it is 100% x86/x86_64
> >> specific.
> >
> > It's possible that x86 needs spectre variant 2 mitigation that isn't
> > necessary on other modern processors like ARM and PowerPC, so let's
> > not rush into general solutions designed around x86..
> >From what I know about variant 2 mitigation it's going to be needed on a
> variety of chip families, not just the Intel architecture.
Yes. I was thinking that it might be possible ignore variant 2
attacks if there were no gadgets available anywhere in the victim
address space, which is true enough but difficult to achieve. That
led me to think that indirect branches didn't matter, until someone
pointed out that the indirect branch attack could be chained. If you
have the first part of a gadget, the read of interesting memory,
followed by an indirect branch, that indirect branch can be spoofed
into code that uses the interesting value in a way that affects cache
state.
--
Alan Modra
Australia Development Lab, IBM