Re: [PATCH bpf-next v3 1/2] bpf: Fix aux usage after do_check_insn()

[Eduard Zingerman]

On Sat, 2025-07-05 at 21:09 +0200, Luis Gerhorst wrote:
> We must terminate the speculative analysis if the just-analyzed insn had
> nospec_result set. Using cur_aux() here is wrong because insn_idx might
> have been incremented by do_check_insn(). Therefore, introduce and use
> insn_aux variable.
> 
> Also change cur_aux(env)->nospec in case do_check_insn() ever manages to
> increment insn_idx but still fail.
> 
> Change the warning to check the insn class (which prevents it from
> triggering for ldimm64, for which nospec_result would not be
> problematic) and use verifier_bug_if().
> 
> In line with Eduard's suggestion, do not introduce prev_aux() because
> that requires one to understand that after do_check_insn() call what was
> current became previous. This would at-least require a comment.
> 
> Fixes: d6f1c85f2253 ("bpf: Fall back to nospec for Spectre v1")
> Reported-by: Paul Chaignon <paul.chaignon@xxxxxxxxx>
> Reported-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> Reported-by: syzbot+dc27c5fb8388e38d2d37@xxxxxxxxxxxxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/bpf/685b3c1b.050a0220.2303ee.0010.GAE@xxxxxxxxxx/
> Link: https://lore.kernel.org/bpf/4266fd5de04092aa4971cbef14f1b4b96961f432.camel@xxxxxxxxx/
> Suggested-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> Signed-off-by: Luis Gerhorst <luis.gerhorst@xxxxxx>
> ---

Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>

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