[PATCH bpf-next v4 05/11] bpf: make BTF pointer type checking generic

[Lorenz Bauer]

Perform BTF type checks if the register we're working on contains a BTF
pointer, rather than if the argument is for a BTF pointer. This is easier
to understand, and allows removing the code from the arg_type checking
section of the function.

Signed-off-by: Lorenz Bauer <l...@cloudflare.com>
Acked-by: Martin KaFai Lau <ka...@fb.com>
---
 kernel/bpf/verifier.c | 38 ++++++++++++++++++++------------------
 1 file changed, 20 insertions(+), 18 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9f95d6d55c5f..99c0d7adcb1e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4001,27 +4001,9 @@ static int check_func_arg(struct bpf_verifier_env *env, 
u32 arg,
                                goto err_type;
                }
        } else if (arg_type == ARG_PTR_TO_BTF_ID) {
-               const u32 *btf_id = fn->arg_btf_id[arg];
-
                expected_type = PTR_TO_BTF_ID;
                if (type != expected_type)
                        goto err_type;
-
-               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 (arg_type == ARG_PTR_TO_SPIN_LOCK) {
                if (meta->func_id == BPF_FUNC_spin_lock) {
                        if (process_spin_lock(env, regno, true))
@@ -4076,6 +4058,26 @@ static int check_func_arg(struct bpf_verifier_env *env, 
u32 arg,
                return -EFAULT;
        }
 
+       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;
+               }
+       }
+
        if (arg_type == ARG_CONST_MAP_PTR) {
                /* bpf_map_xxx(map_ptr) call: remember that map_ptr */
                meta->map_ptr = reg->map_ptr;
-- 
2.25.1