netdev - [PATCH RFC v2 bpf-next 1/2] bpf: Move the PTR_TO_BTF_ID check to check_reg

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Message-ID: <20200915231903.1306553-1-kafai@fb.com>
Date:   Tue, 15 Sep 2020 16:19:03 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     <bpf@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>,
        Lorenz Bauer <lmb@...udflare.com>, <netdev@...r.kernel.org>
Subject: [PATCH RFC v2 bpf-next 1/2] bpf: Move the PTR_TO_BTF_ID check to check_reg_type()

check_reg_type() checks whether a reg can be used as an arg of a
func_proto.  For PTR_TO_BTF_ID, the check is actually not
completely done until the reg->btf_id is pointing to a
kernel struct that is acceptable by the func_proto.

Thus, this patch moves the btf_id check into check_reg_type().
The compatible_reg_types[] usage is localized in check_reg_type()
now which I found it easier to reason in the next patch.

The "if (!btf_id) verbose(...); " is removed for now since it won't
happen.  It will be added back in the next patch with new error log
specific to mis-configured compatible_reg_types[].

Signed-off-by: Martin KaFai Lau <kafai@...com>
---
 kernel/bpf/verifier.c | 65 +++++++++++++++++++++++--------------------
 1 file changed, 35 insertions(+), 30 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8fdef5656e7f..3a5932bd7c22 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3981,20 +3981,29 @@ static const struct bpf_reg_types *compatible_reg_types[] = {
 	[__BPF_ARG_TYPE_MAX]		= NULL,
 };
 
-static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
-			  const struct bpf_reg_types *compatible)
+static int check_reg_type(struct bpf_verifier_env *env, u32 arg,
+			  enum bpf_arg_type arg_type,
+			  const struct bpf_func_proto *fn)
 {
+	u32 regno = BPF_REG_1 + arg;
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
 	enum bpf_reg_type expected, type = reg->type;
+	const struct bpf_reg_types *compatible;
 	int i, j;
 
+	compatible = compatible_reg_types[arg_type];
+	if (!compatible) {
+		verbose(env, "verifier internal error: unsupported arg type %d\n", arg_type);
+		return -EFAULT;
+	}
+
 	for (i = 0; i < ARRAY_SIZE(compatible->types); i++) {
 		expected = compatible->types[i];
 		if (expected == NOT_INIT)
 			break;
 
 		if (type == expected)
-			return 0;
+			goto found;
 	}
 
 	verbose(env, "R%d type=%s expected=", regno, reg_type_str[type]);
@@ -4002,6 +4011,27 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 		verbose(env, "%s, ", reg_type_str[compatible->types[j]]);
 	verbose(env, "%s\n", reg_type_str[compatible->types[j]]);
 	return -EACCES;
+
+found:
+	if (type == PTR_TO_BTF_ID) {
+		u32 *expected_btf_id = fn->arg_btf_id[arg];
+
+		if (!btf_struct_ids_match(&env->log, reg->off, reg->btf_id,
+					  *expected_btf_id)) {
+			verbose(env, "R%d is a pointer to in-kernel struct %s but %s is expected instead\n",
+				regno, kernel_type_name(reg->btf_id),
+				kernel_type_name(*expected_btf_id));
+			return -EACCES;
+		}
+
+		if (!tnum_is_const(reg->var_off) || reg->var_off.value) {
+			verbose(env, "R%d is a pointer to in-kernel struct with non-zero offset\n",
+				regno);
+			return -EACCES;
+		}
+	}
+
+	return 0;
 }
 
 static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
@@ -4011,7 +4041,6 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 	u32 regno = BPF_REG_1 + arg;
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
 	enum bpf_arg_type arg_type = fn->arg_type[arg];
-	const struct bpf_reg_types *compatible;
 	enum bpf_reg_type type = reg->type;
 	int err = 0;
 
@@ -4051,35 +4080,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		 */
 		goto skip_type_check;
 
-	compatible = compatible_reg_types[arg_type];
-	if (!compatible) {
-		verbose(env, "verifier internal error: unsupported arg type %d\n", arg_type);
-		return -EFAULT;
-	}
-
-	err = check_reg_type(env, regno, compatible);
+	err = check_reg_type(env, arg, arg_type, fn);
 	if (err)
 		return err;
 
-	if (type == PTR_TO_BTF_ID) {
-		const u32 *btf_id = fn->arg_btf_id[arg];
-
-		if (!btf_id) {
-			verbose(env, "verifier internal error: missing BTF ID\n");
-			return -EFAULT;
-		}
-
-		if (!btf_struct_ids_match(&env->log, reg->off, reg->btf_id, *btf_id)) {
-			verbose(env, "R%d has incompatible type %s\n", regno,
-				kernel_type_name(reg->btf_id));
-			return -EACCES;
-		}
-		if (!tnum_is_const(reg->var_off) || reg->var_off.value) {
-			verbose(env, "R%d is a pointer to in-kernel struct with non-zero offset\n",
-				regno);
-			return -EACCES;
-		}
-	} else if (type == PTR_TO_CTX) {
+	if (type == PTR_TO_CTX) {
 		err = check_ctx_reg(env, reg, regno);
 		if (err < 0)
 			return err;
-- 
2.24.1