On 2/20/24 11:52 PM, thinker.li@xxxxxxxxx wrote:
From: Kui-Feng Lee <thinker.li@xxxxxxxxx>
Recently, cfi_stubs were introduced. However, existing struct_ops types
that are not in the upstream may not be aware of this, resulting in kernel
crashes. By rejecting struct_ops types that do not provide cfi_stubs during
registration, these crashes can be avoided.
Signed-off-by: Kui-Feng Lee <thinker.li@xxxxxxxxx>
---
kernel/bpf/bpf_struct_ops.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 0d7be97a2411..c1c502caae08 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -302,6 +302,11 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
}
sprintf(value_name, "%s%s", VALUE_PREFIX, st_ops->name);
+ if (!st_ops->cfi_stubs) {
+ pr_warn("struct %s has no cfi_stubs\n", st_ops->name);
+ return -EINVAL;
+ }
+
type_id = btf_find_by_name_kind(btf, st_ops->name,
BTF_KIND_STRUCT);
if (type_id < 0) {
@@ -339,6 +344,7 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
for_each_member(i, t, member) {
const struct btf_type *func_proto;
+ u32 moff;
mname = btf_name_by_offset(btf, member->name_off);
if (!*mname) {
@@ -361,6 +367,17 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
if (!func_proto)
continue;
+ moff = __btf_member_bit_offset(t, member) / 8;
+ err = st_ops->check_member ?
+ st_ops->check_member(t, member, NULL) : 0;
I don't think it is necessary to make check_member more complicated by taking
NULL prog. The struct_ops implementer then needs to handle this extra NULL
prog case.
Have you thought about Alexei's earlier suggestion in v3 to reuse the NULL
member in cfi_stubs to flag unsupported member and remove the unsupported_ops[]
from bpf_tcp_ca.c?
If the verifier can consistently reject loading unsupported bpf prog, it will
not reach the bpf_struct_ops_map_update_elem and then hits the NULL member
in cfi_stubs during map_update_elem.
Untested code:
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 011d54a1dc53..c57cb0e2a8a7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -20370,6 +20370,7 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
u32 btf_id, member_idx;
struct btf *btf;
const char *mname;
+ u32 moff;
if (!prog->gpl_compatible) {
verbose(env, "struct ops programs must have a GPL compatible license\n");
@@ -20417,11 +20418,18 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
return -EINVAL;
}
+ moff = __btf_member_bit_offset(t, member) / 8;
+ if (!*(void **)(st_ops->cfi_stubs + moff)) {
+ verbose(env, "attach to unsupported member %s of struct %s\n",
+ mname, st_ops->name);
+ return -ENOTSUPP;
+ }
+
if (st_ops->check_member) {
int err = st_ops->check_member(t, member, prog);
if (err) {
- verbose(env, "attach to unsupported member %s of struct %s\n",
+ verbose(env, "cannot attach to member %s of struct %s\n",
mname, st_ops->name);
return err;
}
diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
index 7f518ea5f4ac..bcb1fcd00973 100644
--- a/net/ipv4/bpf_tcp_ca.c
+++ b/net/ipv4/bpf_tcp_ca.c
@@ -14,10 +14,6 @@
/* "extern" is to avoid sparse warning. It is only used in bpf_struct_ops.c. */
static struct bpf_struct_ops bpf_tcp_congestion_ops;
-static u32 unsupported_ops[] = {
- offsetof(struct tcp_congestion_ops, get_info),
-};
-
static const struct btf_type *tcp_sock_type;
static u32 tcp_sock_id, sock_id;
static const struct btf_type *tcp_congestion_ops_type;
@@ -45,18 +41,6 @@ static int bpf_tcp_ca_init(struct btf *btf)
return 0;
}
-static bool is_unsupported(u32 member_offset)
-{
- unsigned int i;
-
- for (i = 0; i < ARRAY_SIZE(unsupported_ops); i++) {
- if (member_offset == unsupported_ops[i])
- return true;
- }
-
- return false;
-}
-
static bool bpf_tcp_ca_is_valid_access(int off, int size,
enum bpf_access_type type,
const struct bpf_prog *prog,
@@ -248,15 +232,6 @@ static int bpf_tcp_ca_init_member(const struct btf_type *t,
return 0;
}
-static int bpf_tcp_ca_check_member(const struct btf_type *t,
- const struct btf_member *member,
- const struct bpf_prog *prog)
-{
- if (is_unsupported(__btf_member_bit_offset(t, member) / 8))
- return -ENOTSUPP;
- return 0;
-}
-
static int bpf_tcp_ca_reg(void *kdata)
{
return tcp_register_congestion_control(kdata);
@@ -350,7 +325,6 @@ static struct bpf_struct_ops bpf_tcp_congestion_ops = {
.reg = bpf_tcp_ca_reg,
.unreg = bpf_tcp_ca_unreg,
.update = bpf_tcp_ca_update,
- .check_member = bpf_tcp_ca_check_member,
.init_member = bpf_tcp_ca_init_member,
.init = bpf_tcp_ca_init,
.validate = bpf_tcp_ca_validate,
--
2.34.1
+
+ if (!err && !*(void **)(st_ops->cfi_stubs + moff)) {
+ pr_warn("member %s in struct %s has no cfi stub function\n",
+ mname, st_ops->name);
+ err = -EINVAL;
+ goto errout;
+ }
+
if (btf_distill_func_proto(log, btf,
func_proto, mname,
&st_ops->func_models[i])) {
