On Sat, 3 Feb 2018 18:51:49 -0800
Florian Fainelli [off-list ref] wrote:

Hi Florian,

Hi Marc,

On 02/01/2018 03:07 AM, Marc Zyngier wrote:

quoted

This small series implements some basic BP hardening by invalidating
the BTB on 32bit ARM CPUs that are known to be susceptible to aliasing
attacks (Spectre variant 2). It doesn't help non-ARM 32bit CPUs, nor
32bit kernels that run on 64bit capable CPUs. This series doesn't
mitigate Spectre variant 1 either.

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).

The first patch reuses the Cortex-A8 BTB invalidation in switch_mm and
generalises it to be used on all affected CPUs. The second perform the
same invalidation on prefetch abort outside of the userspace
range. The third one nukes it on guest exit, and results in some major
surgery as we cannot take a branch from the vectors (that, and Thumb2
being a massive pain).

Patches 4 to 6 are doing a similar thing for Cortex-A15, with the
aforementioned ICIALLU.  

I have not had a chance to integrate those patches into the different
downstream branches that we maintain, including upstream, but that's the
plan for next week, because there is nothing else besides spectre &
meltdown anyway right now :)

I would still like to pursue the RFC patch posted to your v3 where the
kernel, if running in secure PL1 tries to set ACTLR[0], except maybe, I
won't try to be too smart and detect the 3 states (firmware set, kernel
set, not set) and just check whether it is set, and if not *and*
HARDEN_BRANCH_PREDICTOR is enabled, then issue a warning?

Sure. That's pretty much orthogonal to this series, so feel free to go
ahead. Please also consider Cortex-A8 when it comes to checking the
ACTLR configuration.

Thanks,

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