[PATCH 6.4 141/800] bpf: Remove anonymous union in bpf_kfunc_call_arg_meta

Greg Kroah-Hartman
2023-07-16T19:59:26Z

From: Dave Marchevsky <davemarchevsky@fb.com>

[ Upstream commit 4d585f48ee6b38c54c075b151c5efd2ff65f8ffd ]

For kfuncs like bpf_obj_drop and bpf_refcount_acquire - which take
user-defined types as input - the verifier needs to track the specific
type passed in when checking a particular kfunc call. This requires
tracking (btf, btf_id) tuple. In commit 7c50b1cb76ac
("bpf: Add bpf_refcount_acquire kfunc") I added an anonymous union with
inner structs named after the specific kfuncs tracking this information,
with the goal of making it more obvious which kfunc this data was being
tracked / expected to be tracked on behalf of.

In a recent series adding a new user of this tuple, Alexei mentioned
that he didn't like this union usage as it doesn't really help with
readability or bug-proofing ([0]). In an offline convo we agreed to
have the tuple be fields (arg_btf, arg_btf_id), with comments in
bpf_kfunc_call_arg_meta definition enumerating the uses of the fields by
kfunc-specific handling logic. Such a pattern is used by struct
bpf_reg_state without trouble.

Accordingly, this patch removes the anonymous union in favor of arg_btf
and arg_btf_id fields and comment enumerating their current uses. The
patch also removes struct btf_and_id, which was only being used by the
removed union's inner structs.

This is a mechanical change, existing linked_list and rbtree tests will
validate that correct (btf, btf_id) are being passed.

[0]: https://lore.kernel.org/bpf/20230505021707.vlyiwy57vwxglbka@dhcp-172-26-102-232.dhcp.thefacebook.com

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/r/20230510213047.1633612-1-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Stable-dep-of: 2140a6e3422d ("bpf: Set kptr_struct_meta for node param to list and rbtree insert funcs")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/verifier.c | 41 ++++++++++++++++++++++-------------------
1 file changed, 22 insertions(+), 19 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fb0aee90ccfaa..4b3d0ead703f4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -273,11 +273,6 @@ struct bpf_call_arg_meta {
struct btf_field *kptr_field;
};

-struct btf_and_id {
- struct btf *btf;
- u32 btf_id;
-};
-
struct bpf_kfunc_call_arg_meta {
/* In parameters */
struct btf *btf;
@@ -296,10 +291,18 @@ struct bpf_kfunc_call_arg_meta {
u64 value;
bool found;
} arg_constant;
- union {
- struct btf_and_id arg_obj_drop;
- struct btf_and_id arg_refcount_acquire;
- };
+
+ /* arg_btf and arg_btf_id are used by kfunc-specific handling,
+ * generally to pass info about user-defined local kptr types to later
+ * verification logic
+ * bpf_obj_drop
+ * Record the local kptr type to be drop'd
+ * bpf_refcount_acquire (via KF_ARG_PTR_TO_REFCOUNTED_KPTR arg type)
+ * Record the local kptr type to be refcount_incr'd
+ */
+ struct btf *arg_btf;
+ u32 arg_btf_id;
+
struct {
struct btf_field *field;
} arg_list_head;
@@ -10493,8 +10496,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
}
if (meta->btf == btf_vmlinux &&
meta->func_id == special_kfunc_list[KF_bpf_obj_drop_impl]) {
- meta->arg_obj_drop.btf = reg->btf;
- meta->arg_obj_drop.btf_id = reg->btf_id;
+ meta->arg_btf = reg->btf;
+ meta->arg_btf_id = reg->btf_id;
}
break;
case KF_ARG_PTR_TO_DYNPTR:
@@ -10683,8 +10686,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
verbose(env, "bpf_refcount_acquire calls are disabled for now\n");
return -EINVAL;
}
- meta->arg_refcount_acquire.btf = reg->btf;
- meta->arg_refcount_acquire.btf_id = reg->btf_id;
+ meta->arg_btf = reg->btf;
+ meta->arg_btf_id = reg->btf_id;
break;
}
}
@@ -10916,12 +10919,12 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
} else if (meta.func_id == special_kfunc_list[KF_bpf_refcount_acquire_impl]) {
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 = meta.arg_refcount_acquire.btf;
- regs[BPF_REG_0].btf_id = meta.arg_refcount_acquire.btf_id;
+ regs[BPF_REG_0].btf = meta.arg_btf;
+ regs[BPF_REG_0].btf_id = meta.arg_btf_id;

insn_aux->kptr_struct_meta =
- btf_find_struct_meta(meta.arg_refcount_acquire.btf,
- meta.arg_refcount_acquire.btf_id);
+ btf_find_struct_meta(meta.arg_btf,
+ meta.arg_btf_id);
} else if (meta.func_id == special_kfunc_list[KF_bpf_list_pop_front] ||
meta.func_id == special_kfunc_list[KF_bpf_list_pop_back]) {
struct btf_field *field = meta.arg_list_head.field;
@@ -11051,8 +11054,8 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
if (meta.btf == btf_vmlinux && btf_id_set_contains(&special_kfunc_set, meta.func_id)) {
if (meta.func_id == special_kfunc_list[KF_bpf_obj_drop_impl]) {
insn_aux->kptr_struct_meta =
- btf_find_struct_meta(meta.arg_obj_drop.btf,
- meta.arg_obj_drop.btf_id);
+ btf_find_struct_meta(meta.arg_btf,
+ meta.arg_btf_id);
}
}
}
--
2.39.2