Re: [PATCH v2 bpf-next] bpf: Fix latent unsoundness in and/or/xor value tracking

[Edward Cree]

On 04/04/2024 03:40, Harishankar Vishwanathan wrote:
> [...]
> Given the above, please advise if we should backport this patch to older
> kernels (and whether I should use the fixes tag).

I don't feel too strongly about it, and if you or Shung-Hsi still
 think, on reflection, that backporting is desirable, then go ahead
 and keep the Fixes: tag.
But maybe tweak the description so someone doesn't see "latent
 unsoundness" and think they need to CVE and rush this patch out as
 a security thing; it's more like hardening.  *shrug*

>> Commit message could also make clearer that the new code considers whether
>>  the *output* ubounds cross sign, rather than looking at the input bounds
>>  as the previous code did.  At first I was confused as to why XOR didn't
>>  need special handling (since -ve xor -ve is +ve).
> 
> Sounds good regarding making it clearer within the context of what the
> existing code does. However, I wanted to clarify that XOR does indeed use
> the same handling as all the other operations. Could you elaborate on what
> you mean?

Just that if you XOR two negative numbers you get a positive number,
 which isn't true for AND or OR; and my confused little brain thought
 that fact was relevant, which it isn't.

-e