Re: [PATCH v2 1/6] arm64: errata: Assume that unknown CPUs _are_ vulnerable to Spectre BHB

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Hi,

On Thu, Dec 19, 2024 at 9:51 AM Will Deacon <will@xxxxxxxxxx> wrote:
>
> > As of right now, the only CPU IDs added to the "unaffected" list are
> > ARM Cortex A35, A53, and A55. This list was created by looking at
> > older cores listed in cputype.h that weren't listed in the "affected"
> > list previously.
>
> There's a list of affected CPUs from Arm here:
>
> https://developer.arm.com/Arm%20Security%20Center/Spectre-BHB
>
> (obviously only covers their own designs).
>
> So it looks like A510 and A520 should be unaffected too, although I
> didn't check exhaustively.

I was hoping that newer cores would hit the supports_csv2p3() check
and be considered safe, but I guess the white paper explicitly says
that A510 doesn't implement it and is still considered safe. I looked
up the TRM of A520 and it looks like it also doesn't set CSV2P3, so I
guess I'll add that one too.


> It also looks like A715 is affected but the
> whitepaper doesn't tell you what version of 'k' to use...

It doesn't? I see a "k" of 38 there. Wow, and Neoverse N2 needs 132!!!

...though I guess on newer steppings of those chips they'll just use
"clear BHB", which seems available and is the preferred mitigation?





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