Re: [PATCHv7 bpf-next 10/29] bpf: Add multi tracing attach types

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Missing `BPF_TRACE_FENTRY_MULTI` and `BPF_TRACE_FEXIT_MULTI` cases in `btf_validate_prog_ctx_type` causes valid `.multi` programs using `u64 *ctx` to be rejected.
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commit 0330f287f02c3a32c9ab8bf7f4f5a6ad6cf7366f
Author: Jiri Olsa <jolsa@kernel.org>

bpf: Add multi tracing attach types

This commit introduces new program attach types BPF_TRACE_FENTRY_MULTI and 
BPF_TRACE_FEXIT_MULTI to support multi-tracing attachment. Base verifier 
support is added to recognize these types and accept them as sleepable 
programs, while deferring actual target validation to link creation.

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 8ed484cb1a8a4..521ec2a9051ed 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
[ ... ]
> @@ -16314,6 +16314,8 @@ static bool return_retval_range(struct bpf_verifier_env *env, struct bpf_retval_
>  		case BPF_TRACE_FENTRY:
>  		case BPF_TRACE_FEXIT:
>  		case BPF_TRACE_FSESSION:
> +		case BPF_TRACE_FENTRY_MULTI:
> +		case BPF_TRACE_FEXIT_MULTI:

[Severity: High]
Are we missing an update to btf_validate_prog_ctx_type() in kernel/bpf/btf.c
to handle these new multi types?

Currently, BPF_TRACE_FENTRY and BPF_TRACE_FEXIT are explicitly whitelisted
there to allow u64 * as a context type:

kernel/bpf/btf.c:btf_validate_prog_ctx_type() {
    ...
		case BPF_TRACE_FENTRY:
		case BPF_TRACE_FEXIT:
		case BPF_MODIFY_RETURN:
		case BPF_TRACE_FSESSION:
			/* allow u64* as ctx */
			if (btf_is_int(t) && t->size == 8)
				return 0;
			break;
    ...
}

Without adding the new multi types to this switch statement, the verifier
will fall back to the default canonical type (void *) and will reject valid
multi programs that use BPF_PROG and u64 *ctx.

>  			*range = retval_range(0, 0);
>  			break;
>  		case BPF_TRACE_RAW_TP:

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Sashiko AI review · https://sashiko.dev/#/patchset/20260603110554.29590-11-jolsa@kernel.org?part=1