[PATCH bpf-next v5 09/25] bpf: Allow locking bpf_spin_lock in local kptr

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Allow locking a bpf_spin_lock embedded in local kptr, in addition to
already support map value pointers. The handling is similar to that of
map values, by just preserving the reg->id of local kptrs as well, and
adjusting process_spin_lock to work with non-PTR_TO_MAP_VALUE and
remember the id in verifier state.

Refactor the existing process_spin_lock to work with PTR_TO_BTF_ID |
MEM_ALLOC in addition to PTR_TO_MAP_VALUE. We need to update the
reg_may_point_to_spin_lock which is used in mark_ptr_or_null_reg to
preserve reg->id, that will be used in env->cur_state->active_spin_lock
to remember the currently held spin lock.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/helpers.c  |  2 ++
 kernel/bpf/verifier.c | 70 ++++++++++++++++++++++++++++++++-----------
 2 files changed, 55 insertions(+), 17 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 7bc71995f17c..5bc0b9f0f306 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -336,6 +336,7 @@ const struct bpf_func_proto bpf_spin_lock_proto = {
 	.gpl_only	= false,
 	.ret_type	= RET_VOID,
 	.arg1_type	= ARG_PTR_TO_SPIN_LOCK,
+	.arg1_btf_id    = BPF_PTR_POISON,
 };
 
 static inline void __bpf_spin_unlock_irqrestore(struct bpf_spin_lock *lock)
@@ -358,6 +359,7 @@ const struct bpf_func_proto bpf_spin_unlock_proto = {
 	.gpl_only	= false,
 	.ret_type	= RET_VOID,
 	.arg1_type	= ARG_PTR_TO_SPIN_LOCK,
+	.arg1_btf_id    = BPF_PTR_POISON,
 };
 
 void copy_map_value_locked(struct bpf_map *map, void *dst, void *src,
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7dcb4629f764..f1170e9db699 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -453,8 +453,16 @@ static bool reg_type_not_null(enum bpf_reg_type type)
 
 static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg)
 {
-	return reg->type == PTR_TO_MAP_VALUE &&
-	       btf_record_has_field(reg->map_ptr->record, BPF_SPIN_LOCK);
+	struct btf_record *rec = NULL;
+
+	if (reg->type == PTR_TO_MAP_VALUE) {
+		rec = reg->map_ptr->record;
+	} else if (reg->type == (PTR_TO_BTF_ID | MEM_ALLOC)) {
+		struct btf_struct_meta *meta = btf_find_struct_meta(reg->btf, reg->btf_id);
+		if (meta)
+			rec = meta->record;
+	}
+	return btf_record_has_field(rec, BPF_SPIN_LOCK);
 }
 
 static bool type_is_rdonly_mem(u32 type)
@@ -5583,8 +5591,10 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
 	struct bpf_verifier_state *cur = env->cur_state;
 	bool is_const = tnum_is_const(reg->var_off);
-	struct bpf_map *map = reg->map_ptr;
 	u64 val = reg->var_off.value;
+	struct bpf_map *map = NULL;
+	struct btf_record *rec;
+	struct btf *btf = NULL;
 
 	if (!is_const) {
 		verbose(env,
@@ -5592,19 +5602,32 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
 			regno);
 		return -EINVAL;
 	}
-	if (!map->btf) {
-		verbose(env,
-			"map '%s' has to have BTF in order to use bpf_spin_lock\n",
-			map->name);
-		return -EINVAL;
+	if (reg->type == PTR_TO_MAP_VALUE) {
+		map = reg->map_ptr;
+		if (!map->btf) {
+			verbose(env,
+				"map '%s' has to have BTF in order to use bpf_spin_lock\n",
+				map->name);
+			return -EINVAL;
+		}
+		rec = map->record;
+	} else {
+		struct btf_struct_meta *meta;
+
+		btf = reg->btf;
+		meta = btf_find_struct_meta(reg->btf, reg->btf_id);
+		if (meta)
+			rec = meta->record;
 	}
-	if (!btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
-		verbose(env, "map '%s' has no valid bpf_spin_lock\n", map->name);
+
+	if (!btf_record_has_field(rec, BPF_SPIN_LOCK)) {
+		verbose(env, "%s '%s' has no valid bpf_spin_lock\n", map ? "map" : "local",
+			map ? map->name : "kptr");
 		return -EINVAL;
 	}
-	if (map->record->spin_lock_off != val + reg->off) {
+	if (rec->spin_lock_off != val + reg->off) {
 		verbose(env, "off %lld doesn't point to 'struct bpf_spin_lock' that is at %d\n",
-			val + reg->off, map->record->spin_lock_off);
+			val + reg->off, rec->spin_lock_off);
 		return -EINVAL;
 	}
 	if (is_lock) {
@@ -5810,13 +5833,19 @@ static const struct bpf_reg_types int_ptr_types = {
 	},
 };
 
+static const struct bpf_reg_types spin_lock_types = {
+	.types = {
+		PTR_TO_MAP_VALUE,
+		PTR_TO_BTF_ID | MEM_ALLOC,
+	}
+};
+
 static const struct bpf_reg_types fullsock_types = { .types = { PTR_TO_SOCKET } };
 static const struct bpf_reg_types scalar_types = { .types = { SCALAR_VALUE } };
 static const struct bpf_reg_types context_types = { .types = { PTR_TO_CTX } };
 static const struct bpf_reg_types ringbuf_mem_types = { .types = { PTR_TO_MEM | MEM_RINGBUF } };
 static const struct bpf_reg_types const_map_ptr_types = { .types = { CONST_PTR_TO_MAP } };
 static const struct bpf_reg_types btf_ptr_types = { .types = { PTR_TO_BTF_ID } };
-static const struct bpf_reg_types spin_lock_types = { .types = { PTR_TO_MAP_VALUE } };
 static const struct bpf_reg_types percpu_btf_ptr_types = { .types = { PTR_TO_BTF_ID | MEM_PERCPU } };
 static const struct bpf_reg_types func_ptr_types = { .types = { PTR_TO_FUNC } };
 static const struct bpf_reg_types stack_ptr_types = { .types = { PTR_TO_STACK } };
@@ -5941,6 +5970,11 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 				return -EACCES;
 			}
 		}
+	} else if (type_is_local_kptr(reg->type)) {
+		if (meta->func_id != BPF_FUNC_spin_lock && meta->func_id != BPF_FUNC_spin_unlock) {
+			verbose(env, "verifier internal error: unimplemented handling of local kptr\n");
+			return -EFAULT;
+		}
 	}
 
 	return 0;
@@ -6057,7 +6091,8 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		goto skip_type_check;
 
 	/* arg_btf_id and arg_size are in a union. */
-	if (base_type(arg_type) == ARG_PTR_TO_BTF_ID)
+	if (base_type(arg_type) == ARG_PTR_TO_BTF_ID ||
+	    base_type(arg_type) == ARG_PTR_TO_SPIN_LOCK)
 		arg_btf_id = fn->arg_btf_id[arg];
 
 	err = check_reg_type(env, regno, arg_type, arg_btf_id, meta);
@@ -6675,9 +6710,10 @@ static bool check_btf_id_ok(const struct bpf_func_proto *fn)
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(fn->arg_type); i++) {
-		if (base_type(fn->arg_type[i]) == ARG_PTR_TO_BTF_ID && !fn->arg_btf_id[i])
-			return false;
-
+		if (base_type(fn->arg_type[i]) == ARG_PTR_TO_BTF_ID)
+			return !!fn->arg_btf_id[i];
+		if (base_type(fn->arg_type[i]) == ARG_PTR_TO_SPIN_LOCK)
+			return fn->arg_btf_id[i] == BPF_PTR_POISON;
 		if (base_type(fn->arg_type[i]) != ARG_PTR_TO_BTF_ID && fn->arg_btf_id[i] &&
 		    /* arg_btf_id and arg_size are in a union. */
 		    (base_type(fn->arg_type[i]) != ARG_PTR_TO_MEM ||
-- 
2.38.1