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

Hi,

On Thu, Dec 19, 2024 at 9:51 AM Will Deacon [off-list ref] wrote:

quoted

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?