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SubjectRe: [PATCH bpf-next v2] bpf: btf: limit logging of ignored BTF mismatches
On Thu, Dec 15, 2022 at 9:06 PM Yonghong Song <yhs@meta.com> wrote:
>
>
>
> 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.
>

Seems like we are also using log->level == BPF_LOG_KERNEL check for
when working with kernel BTFs, so let's stick to the same pattern?


> > +
> > __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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