On Wed, Jul 22, 2020 at 2:13 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Adding btf_struct_ids_match function to check if given address provided
> by BTF object + offset is also address of another nested BTF object.
>
> This allows to pass an argument to helper, which is defined via parent
> BTF object + offset, like for bpf_d_path (added in following changes):
>
> SEC("fentry/filp_close")
> int BPF_PROG(prog_close, struct file *file, void *id)
> {
> ...
> ret = bpf_d_path(&file->f_path, ...
>
> The first bpf_d_path argument is hold by verifier as BTF file object
> plus offset of f_path member.
>
> The btf_struct_ids_match function will walk the struct file object and
> check if there's nested struct path object on the given offset.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> include/linux/bpf.h | 2 ++
> kernel/bpf/btf.c | 29 +++++++++++++++++++++++++++++
> kernel/bpf/verifier.c | 18 ++++++++++++------
> 3 files changed, 43 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index bae557ff2da8..c981e258fed3 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1306,6 +1306,8 @@ int btf_struct_access(struct bpf_verifier_log *log,
> const struct btf_type *t, int off, int size,
> enum bpf_access_type atype,
> u32 *next_btf_id);
> +bool btf_struct_ids_match(struct bpf_verifier_log *log,
> + int off, u32 id, u32 mid);
> int btf_resolve_helper_id(struct bpf_verifier_log *log,
> const struct bpf_func_proto *fn, int);
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 1ab5fd5bf992..562d4453fad3 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -4140,6 +4140,35 @@ int btf_struct_access(struct bpf_verifier_log *log,
> return -EINVAL;
> }
>
> +bool btf_struct_ids_match(struct bpf_verifier_log *log,
> + int off, u32 id, u32 mid)
> +{
> + const struct btf_type *type;
> + u32 nid;
> + int err;
> +
mid and nid are terrible names, especially as an input argument name.
mid == need_type_id? nid == cur_type_id or something along those
lines?
> + do {
> + type = btf_type_by_id(btf_vmlinux, id);
> + if (!type)
> + return false;
> + err = btf_struct_walk(log, type, off, 1, &nid);
> + if (err < 0)
> + return false;
> +
> + /* We found nested struct object. If it matches
> + * the requested ID, we're done. Otherwise let's
> + * continue the search with offset 0 in the new
> + * type.
> + */
> + if (err == walk_struct && mid == nid)
> + return true;
> + off = 0;
> + id = nid;
> + } while (err == walk_struct);
This seems like a slightly more obvious control flow:
again:
...
if (err != walk_struct)
return false;
if (mid != nid) {
off = 0;
id = nid;
goto again;
}
return true;
> +
> + return false;
> +}
> +
> int btf_resolve_helper_id(struct bpf_verifier_log *log,
> const struct bpf_func_proto *fn, int arg)
> {
[...]
