Re: [PATCH v8 bpf-next 07/13] bpf: Add btf_struct_ids_match function

On Wed, Jul 29, 2020 at 10:51:26AM -0700, Andrii Nakryiko wrote:

On Wed, Jul 29, 2020 at 9:04 AM Jiri Olsa [off-list ref] wrote:

quoted

On Tue, Jul 28, 2020 at 04:35:16PM -0700, Andrii Nakryiko wrote:

SNIP

quoted

quoted

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)

just realized that if id == mid and off == 0, btf_struct_ids_match()
will return false. Right now verifier is careful to not call
btf_struct_ids_match in such case, but I wonder if it's better to make
that (common) case also work?

right, also we should call btf_struct_ids_match when
IDs are equal and off != 0, which we don't do now

jirka