Commit d9ab2f76 authored by Eduard Zingerman's avatar Eduard Zingerman Committed by Andrii Nakryiko
Browse files

libbpf: Tie struct_ops programs to kernel BTF ids, not to local ids 



Enforce the following existing limitation on struct_ops programs based
on kernel BTF id instead of program-local BTF id:

    struct_ops BPF prog can be re-used between multiple .struct_ops &
    .struct_ops.link as long as it's the same struct_ops struct
    definition and the same function pointer field

This allows reusing same BPF program for versioned struct_ops map
definitions, e.g.:

    SEC("struct_ops/test")
    int BPF_PROG(foo) { ... }

    struct some_ops___v1 { int (*test)(void); };
    struct some_ops___v2 { int (*test)(void); };

    SEC(".struct_ops.link") struct some_ops___v1 a = { .test = foo }
    SEC(".struct_ops.link") struct some_ops___v2 b = { .test = foo }

Signed-off-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240306104529.6453-3-eddyz87@gmail.com
parent a2a5172c

tools/lib/bpf/libbpf.c

+26 −23
Original line number Diff line number Diff line
@@ -1146,8 +1146,32 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map) 


			if (mod_btf)

				prog->attach_btf_obj_fd = mod_btf->fd;



			/* if we haven't yet processed this BPF program, record proper

			 * attach_btf_id and member_idx

			 */

			if (!prog->attach_btf_id) {

				prog->attach_btf_id = kern_type_id;

				prog->expected_attach_type = kern_member_idx;

			}



			/* struct_ops BPF prog can be re-used between multiple

			 * .struct_ops & .struct_ops.link as long as it's the

			 * same struct_ops struct definition and the same

			 * function pointer field

			 */

			if (prog->attach_btf_id != kern_type_id) {

				pr_warn("struct_ops init_kern %s func ptr %s: invalid reuse of prog %s in sec %s with type %u: attach_btf_id %u != kern_type_id %u\n",

					map->name, mname, prog->name, prog->sec_name, prog->type,

					prog->attach_btf_id, kern_type_id);

				return -EINVAL;

			}

			if (prog->expected_attach_type != kern_member_idx) {

				pr_warn("struct_ops init_kern %s func ptr %s: invalid reuse of prog %s in sec %s with type %u: expected_attach_type %u != kern_member_idx %u\n",

					map->name, mname, prog->name, prog->sec_name, prog->type,

					prog->expected_attach_type, kern_member_idx);

				return -EINVAL;

			}



			st_ops->kern_func_off[i] = kern_data_off + kern_moff;
@@ -9428,27 +9452,6 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj, 
			return -EINVAL;

		}



		/* if we haven't yet processed this BPF program, record proper

		 * attach_btf_id and member_idx

		 */

		if (!prog->attach_btf_id) {

			prog->attach_btf_id = st_ops->type_id;

			prog->expected_attach_type = member_idx;

		}



		/* struct_ops BPF prog can be re-used between multiple

		 * .struct_ops & .struct_ops.link as long as it's the

		 * same struct_ops struct definition and the same

		 * function pointer field

		 */

		if (prog->attach_btf_id != st_ops->type_id ||

		    prog->expected_attach_type != member_idx) {

			pr_warn("struct_ops reloc %s: cannot use prog %s in sec %s with type %u attach_btf_id %u expected_attach_type %u for func ptr %s\n",

				map->name, prog->name, prog->sec_name, prog->type,

				prog->attach_btf_id, prog->expected_attach_type, name);

			return -EINVAL;

		}



		st_ops->progs[member_idx] = prog;



		/* st_ops->data will be exposed to users, being returned by