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().
"arg_type" and "arg_btf_id" are passed to check_reg_type() instead of
"compatible".  The compatible_reg_types[] usage is localized in
check_reg_type() now.

The "if (!btf_id) verbose(...); " is also removed since it won't happen.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Lorenz Bauer <lmb@cloudflare.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200925000344.3854828-1-kafai@fb.com

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 42dee5d..945fa2b 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4028,19 +4028,27 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
 };
 
 static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
-                         const struct bpf_reg_types *compatible)
+                         enum bpf_arg_type arg_type,
+                         const u32 *arg_btf_id)
 {
        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]);
@@ -4048,6 +4056,25 @@ 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) {
+               if (!btf_struct_ids_match(&env->log, reg->off, reg->btf_id,
+                                         *arg_btf_id)) {
+                       verbose(env, "R%d is of type %s but %s is expected\n",
+                               regno, kernel_type_name(reg->btf_id),
+                               kernel_type_name(*arg_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,
@@ -4057,7 +4084,6 @@ 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;
 
@@ -4097,35 +4123,11 @@ 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, regno, arg_type, fn->arg_btf_id[arg]);
        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 is of type %s but %s is expected\n",
-                               regno, kernel_type_name(reg->btf_id), kernel_type_name(*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;