bpf: Refactor ARG_PTR_TO_DYNPTR checks into process_dynptr_func

ARG_PTR_TO_DYNPTR is akin to ARG_PTR_TO_TIMER, ARG_PTR_TO_KPTR, where
the underlying register type is subjected to more special checks to
determine the type of object represented by the pointer and its state
consistency.

Move dynptr checks to their own 'process_dynptr_func' function so that
is consistent and in-line with existing code. This also makes it easier
to reuse this code for kfunc handling.

Then, reuse this consolidated function in kfunc dynptr handling too.
Note that for kfuncs, the arg_type constraint of DYNPTR_TYPE_LOCAL has
been lifted.

Acked-by: David Vernet <[e-mail]>
Acked-by: Joanne Koong <[e-mail]>
Signed-off-by: Kumar Kartikeya Dwivedi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

include/linux/bpf_verifier.h

···
 			   enum bpf_arg_type arg_type);
 int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
 		   u32 regno, u32 mem_size);
-bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
-			      struct bpf_reg_state *reg);
-bool is_dynptr_type_expected(struct bpf_verifier_env *env,
-			     struct bpf_reg_state *reg,
-			     enum bpf_arg_type arg_type);
+struct bpf_call_arg_meta;
+int process_dynptr_func(struct bpf_verifier_env *env, int regno,
+			enum bpf_arg_type arg_type, struct bpf_call_arg_meta *meta);
 
 /* this lives here instead of in bpf.h because it needs to dereference tgt_prog */
 static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,

kernel/bpf/verifier.c

···
 	return true;
 }
 
-bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
-			      struct bpf_reg_state *reg)
+static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
 {
 	struct bpf_func_state *state = func(env, reg);
 	int spi = get_spi(reg->off);
···
 	return true;
 }
 
-bool is_dynptr_type_expected(struct bpf_verifier_env *env,
-			     struct bpf_reg_state *reg,
-			     enum bpf_arg_type arg_type)
+static bool is_dynptr_type_expected(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+				    enum bpf_arg_type arg_type)
 {
 	struct bpf_func_state *state = func(env, reg);
 	enum bpf_dynptr_type dynptr_type;
···
 	return 0;
 }
 
+int process_dynptr_func(struct bpf_verifier_env *env, int regno,
+			enum bpf_arg_type arg_type,
+			struct bpf_call_arg_meta *meta)
+{
+	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
+
+	/* We only need to check for initialized / uninitialized helper
+	 * dynptr args if the dynptr is not PTR_TO_DYNPTR, as the
+	 * assumption is that if it is, that a helper function
+	 * initialized the dynptr on behalf of the BPF program.
+	 */
+	if (base_type(reg->type) == PTR_TO_DYNPTR)
+		return 0;
+	if (arg_type & MEM_UNINIT) {
+		if (!is_dynptr_reg_valid_uninit(env, reg)) {
+			verbose(env, "Dynptr has to be an uninitialized dynptr\n");
+			return -EINVAL;
+		}
+
+		/* We only support one dynptr being uninitialized at the moment,
+		 * which is sufficient for the helper functions we have right now.
+		 */
+		if (meta->uninit_dynptr_regno) {
+			verbose(env, "verifier internal error: multiple uninitialized dynptr args\n");
+			return -EFAULT;
+		}
+
+		meta->uninit_dynptr_regno = regno;
+	} else {
+		if (!is_dynptr_reg_valid_init(env, reg)) {
+			verbose(env,
+				"Expected an initialized dynptr as arg #%d\n",
+				regno);
+			return -EINVAL;
+		}
+
+		if (!is_dynptr_type_expected(env, reg, arg_type)) {
+			const char *err_extra = "";
+
+			switch (arg_type & DYNPTR_TYPE_FLAG_MASK) {
+			case DYNPTR_TYPE_LOCAL:
+				err_extra = "local";
+				break;
+			case DYNPTR_TYPE_RINGBUF:
+				err_extra = "ringbuf";
+				break;
+			default:
+				err_extra = "<unknown>";
+				break;
+			}
+			verbose(env,
+				"Expected a dynptr of type %s as arg #%d\n",
+				err_extra, regno);
+			return -EINVAL;
+		}
+	}
+	return 0;
+}
+
 static bool arg_type_is_mem_size(enum bpf_arg_type type)
 {
 	return type == ARG_CONST_SIZE ||
···
 		err = check_mem_size_reg(env, reg, regno, true, meta);
 		break;
 	case ARG_PTR_TO_DYNPTR:
-		/* We only need to check for initialized / uninitialized helper
-		 * dynptr args if the dynptr is not PTR_TO_DYNPTR, as the
-		 * assumption is that if it is, that a helper function
-		 * initialized the dynptr on behalf of the BPF program.
-		 */
-		if (base_type(reg->type) == PTR_TO_DYNPTR)
-			break;
-		if (arg_type & MEM_UNINIT) {
-			if (!is_dynptr_reg_valid_uninit(env, reg)) {
-				verbose(env, "Dynptr has to be an uninitialized dynptr\n");
-				return -EINVAL;
-			}
-
-			/* We only support one dynptr being uninitialized at the moment,
-			 * which is sufficient for the helper functions we have right now.
-			 */
-			if (meta->uninit_dynptr_regno) {
-				verbose(env, "verifier internal error: multiple uninitialized dynptr args\n");
-				return -EFAULT;
-			}
-
-			meta->uninit_dynptr_regno = regno;
-		} else if (!is_dynptr_reg_valid_init(env, reg)) {
-			verbose(env,
-				"Expected an initialized dynptr as arg #%d\n",
-				arg + 1);
-			return -EINVAL;
-		} else if (!is_dynptr_type_expected(env, reg, arg_type)) {
-			const char *err_extra = "";
-
-			switch (arg_type & DYNPTR_TYPE_FLAG_MASK) {
-			case DYNPTR_TYPE_LOCAL:
-				err_extra = "local";
-				break;
-			case DYNPTR_TYPE_RINGBUF:
-				err_extra = "ringbuf";
-				break;
-			default:
-				err_extra = "<unknown>";
-				break;
-			}
-			verbose(env,
-				"Expected a dynptr of type %s as arg #%d\n",
-				err_extra, arg + 1);
-			return -EINVAL;
-		}
+		if (process_dynptr_func(env, regno, arg_type, meta))
+			return -EACCES;
 		break;
 	case ARG_CONST_ALLOC_SIZE_OR_ZERO:
 		if (!tnum_is_const(reg->var_off)) {
···
 				return ret;
 			break;
 		case KF_ARG_PTR_TO_DYNPTR:
-			if (reg->type != PTR_TO_STACK) {
-				verbose(env, "arg#%d expected pointer to stack\n", i);
+			if (reg->type != PTR_TO_STACK &&
+			    reg->type != PTR_TO_DYNPTR) {
+				verbose(env, "arg#%d expected pointer to stack or dynptr_ptr\n", i);
 				return -EINVAL;
 			}
 
-			if (!is_dynptr_reg_valid_init(env, reg)) {
-				verbose(env, "arg#%d pointer type %s %s must be valid and initialized\n",
-					i, btf_type_str(ref_t), ref_tname);
-				return -EINVAL;
-			}
-
-			if (!is_dynptr_type_expected(env, reg, ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_LOCAL)) {
-				verbose(env, "arg#%d pointer type %s %s points to unsupported dynamic pointer type\n",
-					i, btf_type_str(ref_t), ref_tname);
-				return -EINVAL;
-			}
+			ret = process_dynptr_func(env, regno, ARG_PTR_TO_DYNPTR, NULL);
+			if (ret < 0)
+				return ret;
 			break;
 		case KF_ARG_PTR_TO_LIST_HEAD:
 			if (reg->type != PTR_TO_MAP_VALUE &&

tools/testing/selftests/bpf/prog_tests/kfunc_dynptr_param.c

···
 	const char *expected_verifier_err_msg;
 	int expected_runtime_err;
 } kfunc_dynptr_tests[] = {
-	{"dynptr_type_not_supp",
-	 "arg#0 pointer type STRUCT bpf_dynptr_kern points to unsupported dynamic pointer type", 0},
-	{"not_valid_dynptr",
-	 "arg#0 pointer type STRUCT bpf_dynptr_kern must be valid and initialized", 0},
-	{"not_ptr_to_stack", "arg#0 expected pointer to stack", 0},
+	{"not_valid_dynptr", "Expected an initialized dynptr as arg #1", 0},
+	{"not_ptr_to_stack", "arg#0 expected pointer to stack or dynptr_ptr", 0},
 	{"dynptr_data_null", NULL, -EBADMSG},
 };
 

tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c

···
 char _license[] SEC("license") = "GPL";
 
 SEC("?lsm.s/bpf")
-int BPF_PROG(dynptr_type_not_supp, int cmd, union bpf_attr *attr,
-	     unsigned int size)
-{
-	char write_data[64] = "hello there, world!!";
-	struct bpf_dynptr ptr;
-
-	bpf_ringbuf_reserve_dynptr(&ringbuf, sizeof(write_data), 0, &ptr);
-
-	return bpf_verify_pkcs7_signature(&ptr, &ptr, NULL);
-}
-
-SEC("?lsm.s/bpf")
 int BPF_PROG(not_valid_dynptr, int cmd, union bpf_attr *attr, unsigned int size)
 {
 	unsigned long val;