bpf: reuse btf_prepare_func_args() check for main program BTF validation

Instead of btf_check_subprog_arg_match(), use btf_prepare_func_args()
logic to validate "trustworthiness" of main BPF program's BTF information,
if it is present.

We ignored results of original BTF check anyway, often times producing
confusing and ominously-sounding "reg type unsupported for arg#0
function" message, which has no apparent effect on program correctness
and verification process.

All the -EFAULT returning sanity checks are already performed in
check_btf_info_early(), so there is zero reason to have this duplication
of logic between btf_check_subprog_call() and btf_check_subprog_arg_match().
Dropping btf_check_subprog_arg_match() simplifies
btf_check_func_arg_match() further removing `bool processing_call` flag.

One subtle bit that was done by btf_check_subprog_arg_match() was
potentially marking main program's BTF as unreliable. We do this
explicitly now with a dedicated simple check, preserving the original
behavior, but now based on well factored btf_prepare_func_args() logic.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231215011334.2307144-3-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 3 insertions, 47 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index be2104e5f2f5..33d9a1c73f6e 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6768,8 +6768,7 @@ int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *pr
 static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 				    const struct btf *btf, u32 func_id,
 				    struct bpf_reg_state *regs,
-				    bool ptr_to_mem_ok,
-				    bool processing_call)
+				    bool ptr_to_mem_ok)
 {
 	enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
 	struct bpf_verifier_log *log = &env->log;
@@ -6842,7 +6841,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 					i, btf_type_str(t));
 				return -EINVAL;
 			}
-		} else if (ptr_to_mem_ok && processing_call) {
+		} else if (ptr_to_mem_ok) {
 			const struct btf_type *resolve_ret;
 			u32 type_size;
 
@@ -6867,55 +6866,12 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 	return 0;
 }
 
-/* Compare BTF of a function declaration with given bpf_reg_state.
- * Returns:
- * EFAULT - there is a verifier bug. Abort verification.
- * EINVAL - there is a type mismatch or BTF is not available.
- * 0 - BTF matches with what bpf_reg_state expects.
- * Only PTR_TO_CTX and SCALAR_VALUE states are recognized.
- */
-int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
-				struct bpf_reg_state *regs)
-{
-	struct bpf_prog *prog = env->prog;
-	struct btf *btf = prog->aux->btf;
-	bool is_global;
-	u32 btf_id;
-	int err;
-
-	if (!prog->aux->func_info)
-		return -EINVAL;
-
-	btf_id = prog->aux->func_info[subprog].type_id;
-	if (!btf_id)
-		return -EFAULT;
-
-	if (prog->aux->func_info_aux[subprog].unreliable)
-		return -EINVAL;
-
-	is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
-	err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, false);
-
-	/* Compiler optimizations can remove arguments from static functions
-	 * or mismatched type can be passed into a global function.
-	 * In such cases mark the function as unreliable from BTF point of view.
-	 */
-	if (err)
-		prog->aux->func_info_aux[subprog].unreliable = true;
-	return err;
-}
-
 /* Compare BTF of a function call with given bpf_reg_state.
  * Returns:
  * EFAULT - there is a verifier bug. Abort verification.
  * EINVAL - there is a type mismatch or BTF is not available.
  * 0 - BTF matches with what bpf_reg_state expects.
  * Only PTR_TO_CTX and SCALAR_VALUE states are recognized.
- *
- * NOTE: the code is duplicated from btf_check_subprog_arg_match()
- * because btf_check_func_arg_match() is still doing both. Once that
- * function is split in 2, we can call from here btf_check_subprog_arg_match()
- * first, and then treat the calling part in a new code path.
  */
 int btf_check_subprog_call(struct bpf_verifier_env *env, int subprog,
 			   struct bpf_reg_state *regs)
@@ -6937,7 +6893,7 @@ int btf_check_subprog_call(struct bpf_verifier_env *env, int subprog,
 		return -EINVAL;
 
 	is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
-	err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, true);
+	err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global);
 
 	/* Compiler optimizations can remove arguments from static functions
 	 * or mismatched type can be passed into a global function.