[PATCH bpf-next v2 07/11] bpf: Check subprog arena arguments in the common path

[Amery Hung <ameryhung@gmail.com>]

ARG_PTR_TO_ARENA accepts both arena pointers and scalars. The existing
BPF-subprogram contract includes a constant-zero scalar; it is an arena
address value rather than a conventional pointer rejected by
nullability checking.

Kfunc prototype generation already records this zero acceptance with
PTR_MAYBE_NULL for both arena suffixes; separate JIT metadata determines
whether the kernel callee receives the arena base or NULL. Apply the same
call-site representation to the temporary BPF-subprogram prototype, then
extend the guarded check_func_arg() path to cover arena arguments.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
---
 kernel/bpf/verifier.c | 18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 47ad4f92ef67..237b81ee3159 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10815,6 +10815,8 @@ static void gen_subprog_arg_proto(const struct bpf_subprog_info *sub, const stru
 			 * to protect against invalid memory access.
 			 */
 			arg_type = ARG_IGNORE;
+		} else if (base_type(arg_type) == ARG_PTR_TO_ARENA) {
+			arg_type |= PTR_MAYBE_NULL;
 		}
 		proto->arg_type[arg] = arg_type;
 		t = btf_type_skip_modifiers(btf, args[arg].type, NULL);
@@ -10880,7 +10882,8 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
 		nslots = btf_arg_slots(t);
 
 		if (arg_type == ARG_SCALAR || arg_type == ARG_IGNORE ||
-		    arg_type == ARG_PTR_TO_CTX) {
+		    arg_type == ARG_PTR_TO_CTX ||
+		    base_type(arg_type) == ARG_PTR_TO_ARENA) {
 			ret = check_func_arg(env, arg, slot, 0, &meta, env->insn_idx);
 			if (ret)
 				return ret;
@@ -10908,19 +10911,6 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
 					reg_arg_name(env, argno));
 				return -EINVAL;
 			}
-		} else if (base_type(arg_type) == ARG_PTR_TO_ARENA) {
-			/*
-			 * Can pass any value and the kernel won't crash, but
-			 * only PTR_TO_ARENA or SCALAR make sense. Everything
-			 * else is a bug in the bpf program. Point it out to
-			 * the user at the verification time instead of
-			 * run-time debug nightmare.
-			 */
-			if (reg->type != PTR_TO_ARENA && reg->type != SCALAR_VALUE) {
-				bpf_log(log, "%s is not a pointer to arena or scalar.\n",
-					reg_arg_name(env, argno));
-				return -EINVAL;
-			}
 		} else if (arg_type == ARG_PTR_TO_DYNPTR) {
 			ret = check_func_arg_reg_off(env, reg, argno, ARG_PTR_TO_DYNPTR);
 			if (ret)
-- 
2.52.0