bpf: Fix handling maps with no BTF and non-constant offsets for the bpf_wq

Fix handling maps with no BTF and non-constant offsets for the bpf_wq.

This de-duplicates logic with other internal structs (task_work, timer),
keeps error reporting consistent, and makes future changes to the layout
handling centralized.

Fixes: d940c9b ("bpf: add support for KF_ARG_PTR_TO_WORKQUEUE")
Signed-off-by: Mykyta Yatsenko <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Acked-by: Eduard Zingerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: mykyta5

kernel/bpf/verifier.c

@@ -8479,6 +8479,9 @@ static int check_map_field_pointer(struct bpf_verifier_env *env, u32 regno,
 	case BPF_TASK_WORK:
 		field_off = map->record->task_work_off;
 		break;
+	case BPF_WORKQUEUE:
+		field_off = map->record->wq_off;
+		break;
 	default:
 		verifier_bug(env, "unsupported BTF field type: %s\n", struct_name);
 		return -EINVAL;
@@ -8520,13 +8523,17 @@ static int process_wq_func(struct bpf_verifier_env *env, int regno,
 {
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
 	struct bpf_map *map = reg->map_ptr;
-	u64 val = reg->var_off.value;
+	int err;
 
-	if (map->record->wq_off != val + reg->off) {
-		verbose(env, "off %lld doesn't point to 'struct bpf_wq' that is at %d\n",
-			val + reg->off, map->record->wq_off);
-		return -EINVAL;
+	err = check_map_field_pointer(env, regno, BPF_WORKQUEUE);
+	if (err)
+		return err;
+
+	if (meta->map.ptr) {
+		verifier_bug(env, "Two map pointers in a bpf_wq helper");
+		return -EFAULT;
 	}
+
 	meta->map.uid = reg->map_uid;
 	meta->map.ptr = map;
 	return 0;