This patch builds on the previous few locking patches, teaching the
verifier to check whether rbtree's lock is held.
[ RFC Notes:
* After this patch, could change helpers which only can fail due to
dynamic lock check to always succeed, likely allowing us to get rid
of CONDITIONAL_RELEASE logic. But since dynamic lock checking is
almost certainly going to be necessary regardless, didn't do so.
]
Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
---
include/linux/bpf.h | 2 ++
kernel/bpf/rbtree.c | 8 ++++++++
kernel/bpf/verifier.c | 43 +++++++++++++++++++++++++++++++++++++++----
3 files changed, 49 insertions(+), 4 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index d6458aa7b79c..b762c6b3dcfb 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -155,6 +155,8 @@ struct bpf_map_ops {
bpf_callback_t callback_fn,
void *callback_ctx, u64 flags);
+ bool (*map_lock_held)(struct bpf_map *map, void *current_lock);
+
/* BTF id of struct allocated by map_alloc */
int *map_btf_id;
diff --git a/kernel/bpf/rbtree.c b/kernel/bpf/rbtree.c
index 0821e841a518..b5d158254de6 100644
--- a/kernel/bpf/rbtree.c
+++ b/kernel/bpf/rbtree.c
@@ -245,6 +245,13 @@ static int rbtree_map_delete_elem(struct bpf_map *map, void *value)
return -ENOTSUPP;
}
+static bool rbtree_map_lock_held(struct bpf_map *map, void *current_lock)
+{
+ struct bpf_rbtree *tree = container_of(map, struct bpf_rbtree, map);
+
+ return tree->lock == current_lock;
+}
+
BPF_CALL_2(bpf_rbtree_remove, struct bpf_map *, map, void *, value)
{
struct bpf_rbtree *tree = container_of(map, struct bpf_rbtree, map);
@@ -353,4 +360,5 @@ const struct bpf_map_ops rbtree_map_ops = {
.map_delete_elem = rbtree_map_delete_elem,
.map_check_btf = rbtree_map_check_btf,
.map_btf_id = &bpf_rbtree_map_btf_ids[0],
+ .map_lock_held = rbtree_map_lock_held,
};
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f8ba381f1327..3c9af1047d80 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -508,16 +508,25 @@ static bool is_ptr_cast_function(enum bpf_func_id func_id)
func_id == BPF_FUNC_skc_to_tcp_request_sock;
}
+/* These functions can only be called when spinlock associated with rbtree
+ * is held. They all take struct bpf_map ptr to rbtree as their first argument,
+ * so we can verify that the correct lock is held before loading program
+ */
+static bool is_rbtree_lock_check_function(enum bpf_func_id func_id)
+{
+ return func_id == BPF_FUNC_rbtree_add ||
+ func_id == BPF_FUNC_rbtree_remove ||
+ func_id == BPF_FUNC_rbtree_find;
+}
+
/* These functions can only be called when spinlock associated with rbtree
* is held. If they have a callback argument, that callback is not required
* to release active_spin_lock before exiting
*/
static bool is_rbtree_lock_required_function(enum bpf_func_id func_id)
{
- return func_id == BPF_FUNC_rbtree_add ||
- func_id == BPF_FUNC_rbtree_remove ||
- func_id == BPF_FUNC_rbtree_find ||
- func_id == BPF_FUNC_rbtree_unlock;
+ return func_id == BPF_FUNC_rbtree_unlock ||
+ is_rbtree_lock_check_function(func_id);
}
/* These functions are OK to call when spinlock associated with rbtree
@@ -7354,6 +7363,26 @@ static void update_loop_inline_state(struct bpf_verifier_env *env, u32 subprogno
state->callback_subprogno == subprogno);
}
+static int check_rbtree_lock_held(struct bpf_verifier_env *env,
+ struct bpf_map *map)
+{
+ struct bpf_verifier_state *cur = env->cur_state;
+
+ if (!map)
+ return -1;
+
+ if (!cur->active_spin_lock || !cur->maybe_active_spin_lock_addr ||
+ !map || !map->ops->map_lock_held)
+ return -1;
+
+ if (!map->ops->map_lock_held(map, cur->maybe_active_spin_lock_addr)) {
+ verbose(env, "active spin lock doesn't match rbtree's lock\n");
+ return -1;
+ }
+
+ return 0;
+}
+
static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
int *insn_idx_p)
{
@@ -7560,6 +7589,12 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
if (err)
return err;
+ if (is_rbtree_lock_check_function(func_id) &&
+ check_rbtree_lock_held(env, meta.map_ptr)) {
+ verbose(env, "lock associated with rbtree is not held\n");
+ return -EINVAL;
+ }
+
/* reset caller saved regs */
for (i = 0; i < CALLER_SAVED_REGS; i++) {
mark_reg_not_init(env, regs, caller_saved[i]);
--
2.30.2
