[PATCH v2 bpf-next 09/13] bpf: Special verifier handling for bpf_rbtree_{remove, first}

[Dave Marchevsky <davemarchevsky@fb.com>]

Newly-added bpf_rbtree_{remove,first} kfuncs have some special properties
that require handling in the verifier:

  * both bpf_rbtree_remove and bpf_rbtree_first return the type containing
    the bpf_rb_node field, with the offset set to that field's offset,
    instead of a struct bpf_rb_node *
    * mark_reg_graph_node helper added in previous patch generalizes
      this logic, use it

  * bpf_rbtree_remove's node input is a node that's been inserted
    in the tree - a non-owning reference.

  * bpf_rbtree_remove must invalidate non-owning references in order to
    avoid aliasing issue. Add KF_INVALIDATE_NON_OWN flag, which
    indicates that the marked kfunc is a non-owning ref invalidation
    point, and associated verifier logic using previously-added
    invalidate_non_owning_refs helper.

  * Unlike other functions, which convert one of their input arg regs to
    non-owning reference, bpf_rbtree_first takes no arguments and just
    returns a non-owning reference (possibly null)
    * For now verifier logic for this is special-cased instead of
      adding new kfunc flag.

This patch, along with the previous one, complete special verifier
handling for all rbtree API functions added in this series.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
---
 include/linux/btf.h   |  1 +
 kernel/bpf/helpers.c  |  2 +-
 kernel/bpf/verifier.c | 34 ++++++++++++++++++++++++++++------
 3 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 8aee3f7f4248..3663911bb7c0 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -72,6 +72,7 @@
 #define KF_DESTRUCTIVE		(1 << 6) /* kfunc performs destructive actions */
 #define KF_RCU			(1 << 7) /* kfunc only takes rcu pointer arguments */
 #define KF_RELEASE_NON_OWN	(1 << 8) /* kfunc converts its referenced arg into non-owning ref */
+#define KF_INVALIDATE_NON_OWN	(1 << 9) /* kfunc invalidates non-owning refs after return */
 
 /*
  * Return the name of the passed struct, if exists, or halt the build if for
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index de4523c777b7..0e6d010e6423 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2121,7 +2121,7 @@ BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_task_acquire_not_zero, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_release, KF_RELEASE)
-BTF_ID_FLAGS(func, bpf_rbtree_remove, KF_ACQUIRE)
+BTF_ID_FLAGS(func, bpf_rbtree_remove, KF_ACQUIRE | KF_INVALIDATE_NON_OWN)
 BTF_ID_FLAGS(func, bpf_rbtree_add, KF_RELEASE | KF_RELEASE_NON_OWN)
 BTF_ID_FLAGS(func, bpf_rbtree_first, KF_RET_NULL)
 
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 75979f78399d..b4bf3701de7f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8393,6 +8393,11 @@ static bool is_kfunc_release_non_own(struct bpf_kfunc_call_arg_meta *meta)
 	return meta->kfunc_flags & KF_RELEASE_NON_OWN;
 }
 
+static bool is_kfunc_invalidate_non_own(struct bpf_kfunc_call_arg_meta *meta)
+{
+	return meta->kfunc_flags & KF_INVALIDATE_NON_OWN;
+}
+
 static bool is_kfunc_trusted_args(struct bpf_kfunc_call_arg_meta *meta)
 {
 	return meta->kfunc_flags & KF_TRUSTED_ARGS;
@@ -9425,10 +9430,20 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 				verbose(env, "arg#%d expected pointer to allocated object\n", i);
 				return -EINVAL;
 			}
-			if (!reg->ref_obj_id) {
+			if (meta->func_id == special_kfunc_list[KF_bpf_rbtree_remove]) {
+				if (reg->ref_obj_id) {
+					verbose(env, "rbtree_remove node input must be non-owning ref\n");
+					return -EINVAL;
+				}
+				if (in_rbtree_lock_required_cb(env)) {
+					verbose(env, "rbtree_remove not allowed in rbtree cb\n");
+					return -EINVAL;
+				}
+			} else if (!reg->ref_obj_id) {
 				verbose(env, "allocated object must be referenced\n");
 				return -EINVAL;
 			}
+
 			ret = process_kf_arg_ptr_to_rbtree_node(env, reg, regno, meta);
 			if (ret < 0)
 				return ret;
@@ -9665,11 +9680,12 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 				   meta.func_id == special_kfunc_list[KF_bpf_list_pop_back]) {
 				struct btf_field *field = meta.arg_list_head.field;
 
-				mark_reg_known_zero(env, regs, BPF_REG_0);
-				regs[BPF_REG_0].type = PTR_TO_BTF_ID | MEM_ALLOC;
-				regs[BPF_REG_0].btf = field->graph_root.btf;
-				regs[BPF_REG_0].btf_id = field->graph_root.value_btf_id;
-				regs[BPF_REG_0].off = field->graph_root.node_offset;
+				mark_reg_graph_node(regs, BPF_REG_0, &field->graph_root);
+			} else if (meta.func_id == special_kfunc_list[KF_bpf_rbtree_remove] ||
+				   meta.func_id == special_kfunc_list[KF_bpf_rbtree_first]) {
+				struct btf_field *field = meta.arg_rbtree_root.field;
+
+				mark_reg_graph_node(regs, BPF_REG_0, &field->graph_root);
 			} else if (meta.func_id == special_kfunc_list[KF_bpf_cast_to_kern_ctx]) {
 				mark_reg_known_zero(env, regs, BPF_REG_0);
 				regs[BPF_REG_0].type = PTR_TO_BTF_ID | PTR_TRUSTED;
@@ -9735,7 +9751,13 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			if (is_kfunc_ret_null(&meta))
 				regs[BPF_REG_0].id = id;
 			regs[BPF_REG_0].ref_obj_id = id;
+		} else if (meta.func_id == special_kfunc_list[KF_bpf_rbtree_first]) {
+			ref_set_non_owning_lock(env, &regs[BPF_REG_0]);
 		}
+
+		if (is_kfunc_invalidate_non_own(&meta))
+			invalidate_non_owning_refs(env, &env->cur_state->active_lock);
+
 		if (reg_may_point_to_spin_lock(&regs[BPF_REG_0]) && !regs[BPF_REG_0].id)
 			regs[BPF_REG_0].id = ++env->id_gen;
 	} /* else { add_kfunc_call() ensures it is btf_type_is_void(t) } */
-- 
2.30.2