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bpf: Check unsupported ops from the bpf_struct_ops's cfi_stubs

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The bpf_tcp_ca struct_ops currently uses a "u32 unsupported_ops[]"
array to track which ops is not supported.

After cfi_stubs had been added, the function pointer in cfi_stubs is
also NULL for the unsupported ops. Thus, the "u32 unsupported_ops[]"
becomes redundant. This observation was originally brought up in the
bpf/cfi discussion:
https://lore.kernel.org/bpf/CAADnVQJoEkdjyCEJRPASjBw1QGsKYrF33QdMGc1RZa9b88bAEA@mail.gmail.com/

The recent bpf qdisc patch (https://lore.kernel.org/bpf/20240714175130.4051012-6-amery.hung@bytedance.com/)
also needs to specify quite many unsupported ops. It is a good time
to clean it up.

This patch removes the need of "u32 unsupported_ops[]" and tests for null-ness
in the cfi_stubs instead.

Testing the cfi_stubs is done in a new function bpf_struct_ops_supported().
The verifier will call bpf_struct_ops_supported() when loading the
struct_ops program. The ".check_member" is removed from the bpf_tcp_ca
in this patch. ".check_member" could still be useful for other subsytems
to enforce other restrictions (e.g. sched_ext checks for prog->sleepable).

To keep the same error return, ENOTSUPP is used.

Cc: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20240722183049.2254692-2-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
This commit is contained in:
Martin KaFai Lau 2024-07-22 11:30:45 -07:00 committed by Andrii Nakryiko
parent 0d7c06125c
commit e42ac14180
4 changed files with 21 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/linux/bpf.h
View File

@ -1795,6 +1795,7 @@ struct bpf_struct_ops_common_value {
#define BPF_MODULE_OWNER ((void *)((0xeB9FUL << 2) + POISON_POINTER_DELTA))
bool bpf_struct_ops_get(const void *kdata);
void bpf_struct_ops_put(const void *kdata);
int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff);
int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map, void *key,
void *value);
int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks,
@ -1851,6 +1852,10 @@ static inline void bpf_module_put(const void *data, struct module *owner)
{
module_put(owner);
}
static inline int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)
{
return -ENOTSUPP;
}
static inline int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map,
void *key,
void *value)

7
kernel/bpf/bpf_struct_ops.c
View File

@ -1040,6 +1040,13 @@ void bpf_struct_ops_put(const void *kdata)
bpf_map_put(&st_map->map);
}
int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)
{
void *func_ptr = *(void **)(st_ops->cfi_stubs + moff);
return func_ptr ? 0 : -ENOTSUPP;
}
static bool bpf_struct_ops_valid_to_reg(struct bpf_map *map)
{
struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;

10
kernel/bpf/verifier.c
View File

@ -21132,6 +21132,7 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
u32 btf_id, member_idx;
struct btf *btf;
const char *mname;
int err;
if (!prog->gpl_compatible) {
verbose(env, "struct ops programs must have a GPL compatible license\n");
@ -21179,8 +21180,15 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
return -EINVAL;
}
err = bpf_struct_ops_supported(st_ops, __btf_member_bit_offset(t, member) / 8);
if (err) {
verbose(env, "attach to unsupported member %s of struct %s\n",
mname, st_ops->name);
return err;
}
if (st_ops->check_member) {
int err = st_ops->check_member(t, member, prog);
err = st_ops->check_member(t, member, prog);
if (err) {
verbose(env, "attach to unsupported member %s of struct %s\n",

26
net/ipv4/bpf_tcp_ca.c
View File

@ -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,
@ -251,15 +235,6 @@ 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, struct bpf_link *link)
{
return tcp_register_congestion_control(kdata);
@ -354,7 +329,6 @@ 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,