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SubjectRe: [PATCH bpf-next v2] bpf: btf: limit logging of ignored BTF mismatches
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On 12/14/22 4:53 PM, Connor O'Brien wrote:
> Enabling CONFIG_MODULE_ALLOW_BTF_MISMATCH is an indication that BTF
> mismatches are expected and module loading should proceed
> anyway. Logging with pr_warn() on every one of these "benign"
> mismatches creates unnecessary noise when many such modules are
> loaded. Instead, handle this case with a single log warning that BTF
> info may be unavailable.
>
> Mismatches also result in calls to __btf_verifier_log() via
> __btf_verifier_log_type() or btf_verifier_log_member(), adding several
> additional lines of logging per mismatched module. Add checks to these
> paths to skip logging for module BTF mismatches in the "allow
> mismatch" case.
>
> All existing logging behavior is preserved in the default
> CONFIG_MODULE_ALLOW_BTF_MISMATCH=n case.
>
> Signed-off-by: Connor O'Brien <connoro@google.com>

Ack with a few nits below.

Acked-by: Yonghong Song <yhs@fb.com>

> ---
> v2:
> - Use pr_warn_once instead of skipping logging entirely
> - Also skip btf verifier logs for ignored mismatches
>
> v1: https://lore.kernel.org/bpf/20221109024155.2810410-1-connoro@google.com/
> ---
> kernel/bpf/btf.c | 24 +++++++++++++++++++++---
> 1 file changed, 21 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index f7dd8af06413..16b959b49595 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -1404,6 +1404,13 @@ __printf(4, 5) static void __btf_verifier_log_type(struct btf_verifier_env *env,
> if (log->level == BPF_LOG_KERNEL && !fmt)
> return;
>
> + /*
> + * Skip logging when loading module BTF with mismatches permitted
> + */

Just use one line for the above comment.

> + if (env->btf->base_btf && env->btf->kernel_btf &&
> + IS_ENABLED(CONFIG_MODULE_ALLOW_BTF_MISMATCH))
> + return;

I believe env->btf->base_btf alone is enough to test it should be a
module btf. If env->btf->base_btf is true, env->btf->kernel_btf should
also be true. The other way is not true, env->btf->kernel_btf is true,
the btf could be vmlinux (env->btf->base_btf == NULL) or be a module.

> +
> __btf_verifier_log(log, "[%u] %s %s%s",
> env->log_type_id,
> btf_type_str(t),
> @@ -1443,6 +1450,14 @@ static void btf_verifier_log_member(struct btf_verifier_env *env,
>
> if (log->level == BPF_LOG_KERNEL && !fmt)
> return;
> +
> + /*
> + * Skip logging when loading module BTF with mismatches permitted
> + */

Same, just use one line for the above comments.

> + if (env->btf->base_btf && env->btf->kernel_btf &&
> + IS_ENABLED(CONFIG_MODULE_ALLOW_BTF_MISMATCH))
> + return;
> +
> /* The CHECK_META phase already did a btf dump.
> *
> * If member is logged again, it must hit an error in
> @@ -7260,11 +7275,14 @@ static int btf_module_notify(struct notifier_block *nb, unsigned long op,
> }
> btf = btf_parse_module(mod->name, mod->btf_data, mod->btf_data_size);
> if (IS_ERR(btf)) {
> - pr_warn("failed to validate module [%s] BTF: %ld\n",
> - mod->name, PTR_ERR(btf));
> kfree(btf_mod);
> - if (!IS_ENABLED(CONFIG_MODULE_ALLOW_BTF_MISMATCH))
> + if (!IS_ENABLED(CONFIG_MODULE_ALLOW_BTF_MISMATCH)) {
> + pr_warn("failed to validate module [%s] BTF: %ld\n",
> + mod->name, PTR_ERR(btf));
> err = PTR_ERR(btf);
> + } else {
> + pr_warn_once("Kernel module BTF mismatch detected, BTF debug info may be unavailable for some modules\n");
> + }
> goto out;
> }
> err = btf_alloc_id(btf);

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