Re: [syzbot ci] Re: bpf: Use tnums for JEQ/JNE is_branch_taken logic

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2025-08-20 at 13:34 +0200, Paul Chaignon wrote:

[...]

> I have a patch to potentially fix this, but I'm still testing it and
> would prefer to send it separately as it doesn't really relate to my
> current patchset.

I'd like to bring this point again: this is a cat-and-mouse game.
is_scalar_branch_taken() and regs_refine_cond_op() are essentially
same operation and should be treated as such: produce register states
for both branches and prune those that result in an impossible state.
There is nothing wrong with this logically and we haven't got a single
real bug from the invariant violations check if I remember correctly.

Comparing the two functions, it looks like tricky cases are BPF_JE/JNE
and BPF_JSET/JSET|BPF_X. However, given that regs_refine_cond_op() is
called for a false branch with opcode reversed it looks like there is
no issues with these cases.

I'll give this a try.

[...]