On Mon, Nov 28, 2022 at 5:29 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Adding bpf_vma_build_id_parse function to retrieve build id from
> passed vma object and making it available as bpf kfunc.
>
> We can't use build_id_parse directly as kfunc, because we would
> not have control over the build id buffer size provided by user.
>
> Instead we are adding new bpf_vma_build_id_parse function with
> 'build_id__sz' argument that instructs verifier to check for the
> available space in build_id buffer.
>
> This way we check that there's always available memory space
> behind build_id pointer. We also check that the build_id__sz is
> at least BUILD_ID_SIZE_MAX so we can place any buildid in.
>
> The bpf_vma_build_id_parse kfunc is marked as KF_TRUSTED_ARGS,
> so it can be only called with trusted vma objects. These are
> currently provided only by find_vma callback function and
> task_vma iterator program.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> include/linux/bpf.h | 4 ++++
> kernel/trace/bpf_trace.c | 31 +++++++++++++++++++++++++++++++
> 2 files changed, 35 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index c6aa6912ea16..359c8fe11779 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2839,4 +2839,8 @@ static inline bool type_is_alloc(u32 type)
> return type & MEM_ALLOC;
> }
>
> +int bpf_vma_build_id_parse(struct vm_area_struct *vma,
> + unsigned char *build_id,
> + size_t build_id__sz);
> +
> #endif /* _LINUX_BPF_H */
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 3bbd3f0c810c..7340de74531a 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -23,6 +23,7 @@
> #include <linux/sort.h>
> #include <linux/key.h>
> #include <linux/verification.h>
> +#include <linux/buildid.h>
>
> #include <net/bpf_sk_storage.h>
>
> @@ -1383,6 +1384,36 @@ static int __init bpf_key_sig_kfuncs_init(void)
> late_initcall(bpf_key_sig_kfuncs_init);
> #endif /* CONFIG_KEYS */
>
> +int bpf_vma_build_id_parse(struct vm_area_struct *vma,
> + unsigned char *build_id,
> + size_t build_id__sz)
> +{
> + __u32 size;
> + int err;
> +
> + if (build_id__sz < BUILD_ID_SIZE_MAX)
> + return -EINVAL;
> +
> + err = build_id_parse(vma, build_id, &size);
> + return err ?: (int) size;
if err is positive the caller won't be able
to distinguish it vs size.
> +}
> +
> +BTF_SET8_START(tracing_btf_ids)
> +BTF_ID_FLAGS(func, bpf_vma_build_id_parse, KF_TRUSTED_ARGS)
> +BTF_SET8_END(tracing_btf_ids)
> +
> +static const struct btf_kfunc_id_set tracing_kfunc_set = {
> + .owner = THIS_MODULE,
> + .set = &tracing_btf_ids,
> +};
> +
> +static int __init kfunc_tracing_init(void)
> +{
> + return register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &tracing_kfunc_set);
> +}
> +
> +late_initcall(kfunc_tracing_init);
Its own btf_id set and its own late_initcall just for one kfunc?
Please reduce this boilerplate code.
Move it to kernel/bpf/helpers.c ?
