[PATCH v2 0/6] ARM branch predictor hardening

[Marc Zyngier]

On Tue, 16 Jan 2018 09:11:54 -0800
Florian Fainelli <f.fainelli at gmail.com> wrote:

> On 01/10/2018 09:16 AM, Marc Zyngier wrote:
> > On 10/01/18 16:50, Nishanth Menon wrote:  
> >> On 01/08/2018 12:55 PM, Marc Zyngier wrote:  
> >>> This small series implements some basic BP hardening by invalidating
> >>> the BTB on CPUs that are known to be susceptible to aliasing attacks.
> >>>
> >>> These patches are closely modelled against what we do on arm64,
> >>> although simpler as we can rely on an architected instruction to
> >>> perform the invalidation. The notable exception is Cortex-A15, where
> >>> BTB invalidation behaves like a NOP, and the only way to shoot the
> >>> predictor down is to invalidate the icache *and* to have ACTLR[0] set
> >>> to 1 (which is a secure-only operation).
> >>>  
> >>
> >>
> >> btw, just wanted to understand if we had any reasons as to why 
> >> we'arent tagging these for stable? Yes, I am aware of Greg's comments 
> >> in [1], but the v7 series impacts a heck of a lot of existing products 
> >> and is not that extensive to cause too much of a pain is it?
> >>
> >> OR, am I missing some thing else?
> >>
> >> [1] http://www.kroah.com/log/blog/2018/01/06/meltdown-status/  
> > 
> > This is a work in progress. It is not ready for being merged yet. It can
> > be backported to stable after being merged into mainline.  
> 
> When do you expect to post a v3 of these patches? Happy to test anything
> and report back the results. 

I'll probably post another version by the end of the week.

> As Russell pointed out earlier, his test cases against these patches
> + adding special casing for the Brahma-B15 did not result in any
> improvement for his "spectre" or "meltdown" test cases...

These patches are developed to match the recommendations of the CPU
designers, and are only applicable to Cortex-A8, A9, A12, A15 and A17.
On any other CPU, they will not do anything.

I have not seen Russell's test cases, so I cannot comment on them. But
none of this has any impact on Meltdown or Spectre variant-1. This only
addresses Spectre variant-2. If you have one of the above CPUs, and
that these patches do not fix variant-2 for you, please get in touch.

Thanks,

	M.
-- 
Without deviation from the norm, progress is not possible.