bpf: prepare btf_prepare_func_args() for multiple tags per argument

Add btf_arg_tag flags enum to be able to record multiple tags per
argument. Also streamline pointer argument processing some more.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240105000909.2818934-4-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/btf.c

@@ -6946,6 +6946,11 @@ static bool btf_is_dynptr_ptr(const struct btf *btf, const struct btf_type *t)
 	return false;
 }
 
+enum btf_arg_tag {
+	ARG_TAG_CTX = 0x1,
+	ARG_TAG_NONNULL = 0x2,
+};
+
 /* Process BTF of a function to produce high-level expectation of function
  * arguments (like ARG_PTR_TO_CTX, or ARG_PTR_TO_MEM, etc). This information
  * is cached in subprog info for reuse.
@@ -7027,10 +7032,8 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 	 * Only PTR_TO_CTX and SCALAR are supported atm.
 	 */
 	for (i = 0; i < nargs; i++) {
-		bool is_nonnull = false;
 		const char *tag;
-
-		t = btf_type_by_id(btf, args[i].type);
+		u32 tags = 0;
 
 		tag = btf_find_decl_tag_value(btf, fn_t, i, "arg:");
 		if (IS_ERR(tag) && PTR_ERR(tag) == -ENOENT) {
@@ -7048,43 +7051,61 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 				bpf_log(log, "arg#%d type tag is not supported in static functions\n", i);
 				return -EOPNOTSUPP;
 			}
+
 			if (strcmp(tag, "ctx") == 0) {
-				sub->args[i].arg_type = ARG_PTR_TO_CTX;
-				continue;
+				tags |= ARG_TAG_CTX;
+			} else if (strcmp(tag, "nonnull") == 0) {
+				tags |= ARG_TAG_NONNULL;
+			} else {
+				bpf_log(log, "arg#%d has unsupported set of tags\n", i);
+				return -EOPNOTSUPP;
 			}
-			if (strcmp(tag, "nonnull") == 0)
-				is_nonnull = true;
 		}
 
+		t = btf_type_by_id(btf, args[i].type);
 		while (btf_type_is_modifier(t))
 			t = btf_type_by_id(btf, t->type);
-		if (btf_type_is_ptr(t) && btf_get_prog_ctx_type(log, btf, t, prog_type, i)) {
+		if (!btf_type_is_ptr(t))
+			goto skip_pointer;
+
+		if ((tags & ARG_TAG_CTX) || btf_get_prog_ctx_type(log, btf, t, prog_type, i)) {
+			if (tags & ~ARG_TAG_CTX) {
+				bpf_log(log, "arg#%d has invalid combination of tags\n", i);
+				return -EINVAL;
+			}
 			sub->args[i].arg_type = ARG_PTR_TO_CTX;
 			continue;
 		}
-		if (btf_type_is_ptr(t) && btf_is_dynptr_ptr(btf, t)) {
+		if (btf_is_dynptr_ptr(btf, t)) {
+			if (tags) {
+				bpf_log(log, "arg#%d has invalid combination of tags\n", i);
+				return -EINVAL;
+			}
 			sub->args[i].arg_type = ARG_PTR_TO_DYNPTR | MEM_RDONLY;
 			continue;
 		}
-		if (is_global && btf_type_is_ptr(t)) {
+		if (is_global) { /* generic user data pointer */
 			u32 mem_size;
 
 			t = btf_type_skip_modifiers(btf, t->type, NULL);
 			ref_t = btf_resolve_size(btf, t, &mem_size);
 			if (IS_ERR(ref_t)) {
-				bpf_log(log,
-				    "arg#%d reference type('%s %s') size cannot be determined: %ld\n",
+				bpf_log(log, "arg#%d reference type('%s %s') size cannot be determined: %ld\n",
 					i, btf_type_str(t), btf_name_by_offset(btf, t->name_off),
 					PTR_ERR(ref_t));
 				return -EINVAL;
 			}
 
-			sub->args[i].arg_type = is_nonnull ? ARG_PTR_TO_MEM : ARG_PTR_TO_MEM_OR_NULL;
+			sub->args[i].arg_type = ARG_PTR_TO_MEM | PTR_MAYBE_NULL;
+			if (tags & ARG_TAG_NONNULL)
+				sub->args[i].arg_type &= ~PTR_MAYBE_NULL;
 			sub->args[i].mem_size = mem_size;
 			continue;
 		}
-		if (is_nonnull) {
-			bpf_log(log, "arg#%d marked as non-null, but is not a pointer type\n", i);
+
+skip_pointer:
+		if (tags) {
+			bpf_log(log, "arg#%d has pointer tag, but is not a pointer type\n", i);
 			return -EINVAL;
 		}
 		if (btf_type_is_int(t) || btf_is_any_enum(t)) {

kernel/bpf/verifier.c

@@ -20058,7 +20058,6 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
 	state->first_insn_idx = env->subprog_info[subprog].start;
 	state->last_insn_idx = -1;
 
-
 	regs = state->frame[state->curframe]->regs;
 	if (subprog || env->prog->type == BPF_PROG_TYPE_EXT) {
 		const char *sub_name = subprog_name(env, subprog);