[U-Boot] U-Boot, cache speculation side channel attacks and ARM

[Marc Zyngier]

On Fri, 19 Jan 2018 17:10:04 -0600
Nishanth Menon <nm at ti.com> wrote:

> On 01/19/2018 04:21 PM, Mark Kettenis wrote:
> >> Date: Fri, 19 Jan 2018 16:56:14 -0500
> >> From: Tom Rini <trini at konsulko.com>
> >>
> >> Hey all,
> >>
> >> So, now that things have quieted down a little bit in this area, I've
> >> been wondering about something.  Over on the U-Boot side of things, are
> >> there changes we need to make in order to support the kernel side of the
> >> various mitigations properly?  I know that for example currently
> >> https://developer.arm.com/support/security-update talks about ATF
> >> patches, in the context of AArch64 however.  But on the other hand for
> >> variant 2, there's nothing listed on the Linux side for 32bit ARM, but
> >> there is for non-Linux OSes.
> >>
> >> And, in the event I'm also missing something else entirely that we need
> >> to do here, is there something that we need to be doing?  Or is it still
> >> too early at this point in time to know?  
> > 
> > I think that for AArch32, the following bit advice is relevant:
> > 
> >    For Cortex-A15, set ACTLR[0]==1 from early initialization of the
> >    processor, and invalidate the branch predictor by performing an
> >    ICIALLU instruction.
> > 
> > For now OpenBSD assumes that "the firmware" sets ACTLR[0] since this
> > register may be read-only in non-secure mode.  And unless I missed
> > something Linux makes the same assumption.
> > 
> > If U-Boot provides the PSCI implementation it should probably flush
> > the BTB on affected 32-bit processors and should defenitely flush on
> > 64-bit processors.  
> 
> Seeing the traffic in kernel, I think I understand these two I know of 
> at least?
> 
> A8/9/12/17:
> "So without IBE set, as the comments above say, the flush won't do 
> anything."
> https://marc.info/?l=linux-arm-kernel&m=151566145121435&w=2

This applies to A8 only. A9/A12/A17 do not need any additional settings
for BPIALL to work correctly.

> A15: ACTLR
> https://marc.info/?l=linux-arm-kernel&m=151562519425981&w=2
> 
> Am I misunderstanding the list we need to do in u-boot?
> 

A15 requires IBE to be set for ICIALLU to invalidate the branch
predictor.

Thanks,

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