[PATCH v4 bpf-next 02/11] bpf: Improve bpf_reg_state space usage for non-owning ref lock

[Dave Marchevsky <davemarchevsky@fb.com>]

This patch eliminates extra bpf_reg_state memory usage added due to
previous patch keeping a copy of lock identity in reg state for
non-owning refs.

Instead of copying lock identity around, this patch changes
non_owning_ref_lock field to be a bool, taking advantage of the
following:

  * There can currently only be one active lock at a time
  * non-owning refs are only valid in the critical section

So if a verifier_state has an active_lock, any non-owning ref must've
been obtained under that lock, and any non-owning ref not obtained under
that lock must have been invalidated previously. Therefore if a
non-owning ref is associated with a lock, it's the active_lock of the
current state. So we can keep a bool "are we associated with active_lock
of current state" instead of copying lock identity around.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
---
 include/linux/bpf_verifier.h |  2 +-
 kernel/bpf/verifier.c        | 25 ++++++++++---------------
 2 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7b5fbb66446c..d25446dd0413 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -84,7 +84,7 @@ struct bpf_reg_state {
 		struct {
 			struct btf *btf;
 			u32 btf_id;
-			struct bpf_active_lock non_owning_ref_lock;
+			bool non_owning_ref_lock;
 		};
 
 		struct { /* for PTR_TO_MEM | PTR_TO_MEM_OR_NULL */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f693cc97c574..89c09752421c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -190,8 +190,7 @@ struct bpf_verifier_stack_elem {
 
 static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx);
 static int release_reference(struct bpf_verifier_env *env, int ref_obj_id);
-static void invalidate_non_owning_refs(struct bpf_verifier_env *env,
-				       struct bpf_active_lock *lock);
+static void invalidate_non_owning_refs(struct bpf_verifier_env *env);
 static int ref_set_non_owning_lock(struct bpf_verifier_env *env,
 				   struct bpf_reg_state *reg);
 
@@ -1077,9 +1076,8 @@ static void print_verifier_state(struct bpf_verifier_env *env,
 				verbose_a("id=%d", reg->id);
 			if (reg->ref_obj_id)
 				verbose_a("ref_obj_id=%d", reg->ref_obj_id);
-			if (reg->non_owning_ref_lock.ptr)
-				verbose_a("non_own_id=(%p,%d)", reg->non_owning_ref_lock.ptr,
-					  reg->non_owning_ref_lock.id);
+			if (reg->non_owning_ref_lock)
+				verbose_a("%s", "non_own_ref");
 			if (t != SCALAR_VALUE)
 				verbose_a("off=%d", reg->off);
 			if (type_is_pkt_pointer(t))
@@ -5049,7 +5047,7 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
 		}
 
 		if (type_is_alloc(reg->type) && !reg->ref_obj_id &&
-		    !reg->non_owning_ref_lock.ptr) {
+		    !reg->non_owning_ref_lock) {
 			verbose(env, "verifier internal error: ref_obj_id for allocated object must be non-zero\n");
 			return -EFAULT;
 		}
@@ -6056,7 +6054,7 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
 			return -EINVAL;
 		}
 
-		invalidate_non_owning_refs(env, &cur->active_lock);
+		invalidate_non_owning_refs(env);
 
 		cur->active_lock.ptr = NULL;
 		cur->active_lock.id = 0;
@@ -7373,16 +7371,14 @@ static int release_reference(struct bpf_verifier_env *env,
 	return 0;
 }
 
-static void invalidate_non_owning_refs(struct bpf_verifier_env *env,
-				       struct bpf_active_lock *lock)
+static void invalidate_non_owning_refs(struct bpf_verifier_env *env)
 {
 	struct bpf_func_state *unused;
 	struct bpf_reg_state *reg;
 
 	bpf_for_each_reg_in_vstate(env->cur_state, unused, reg, ({
-		if (reg->non_owning_ref_lock.ptr &&
-		    reg->non_owning_ref_lock.ptr == lock->ptr &&
-		    reg->non_owning_ref_lock.id == lock->id)
+		if (type_is_ptr_alloc_obj(reg->type) &&
+		    reg->non_owning_ref_lock)
 			__mark_reg_unknown(env, reg);
 	}));
 }
@@ -8948,13 +8944,12 @@ static int ref_set_non_owning_lock(struct bpf_verifier_env *env, struct bpf_reg_
 		return -EFAULT;
 	}
 
-	if (reg->non_owning_ref_lock.ptr) {
+	if (reg->non_owning_ref_lock) {
 		verbose(env, "verifier internal error: non_owning_ref_lock already set\n");
 		return -EFAULT;
 	}
 
-	reg->non_owning_ref_lock.id = state->active_lock.id;
-	reg->non_owning_ref_lock.ptr = state->active_lock.ptr;
+	reg->non_owning_ref_lock = true;
 	return 0;
 }
 
-- 
2.30.2