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bpf: add fsession support 

The fsession is something that similar to kprobe session. It allow to
attach a single BPF program to both the entry and the exit of the target
functions.

Introduce the struct bpf_fsession_link, which allows to add the link to
both the fentry and fexit progs_hlist of the trampoline.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Co-developed-by: Leon Hwang <leon.hwang@linux.dev>
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20260124062008.8657-2-dongml2@chinatelecom.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
master
Menglong Dong 2026-01-24 14:19:56 +08:00 committed by Alexei Starovoitov
parent c7900f225a
commit 2d419c4465
10 changed files with 97 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
include/linux/bpf.h
View File

@ -1309,6 +1309,7 @@ enum bpf_tramp_prog_type {
BPF_TRAMP_MODIFY_RETURN,
BPF_TRAMP_MAX,
BPF_TRAMP_REPLACE, /* more than MAX */
BPF_TRAMP_FSESSION,
};
struct bpf_tramp_image {
@ -1875,6 +1876,11 @@ struct bpf_tracing_link {
struct bpf_prog *tgt_prog;
};
struct bpf_fsession_link {
struct bpf_tracing_link link;
struct bpf_tramp_link fexit;
};
struct bpf_raw_tp_link {
struct bpf_link link;
struct bpf_raw_event_map *btp;
@ -2169,6 +2175,19 @@ static inline void bpf_struct_ops_desc_release(struct bpf_struct_ops_desc *st_op
#endif
static inline int bpf_fsession_cnt(struct bpf_tramp_links *links)
{
struct bpf_tramp_links fentries = links[BPF_TRAMP_FENTRY];
int cnt = 0;
for (int i = 0; i < links[BPF_TRAMP_FENTRY].nr_links; i++) {
if (fentries.links[i]->link.prog->expected_attach_type == BPF_TRACE_FSESSION)
cnt++;
}
return cnt;
}
int bpf_prog_ctx_arg_info_init(struct bpf_prog *prog,
const struct bpf_ctx_arg_aux *info, u32 cnt);

1
include/uapi/linux/bpf.h
View File

@ -1145,6 +1145,7 @@ enum bpf_attach_type {
BPF_NETKIT_PEER,
BPF_TRACE_KPROBE_SESSION,
BPF_TRACE_UPROBE_SESSION,
BPF_TRACE_FSESSION,
__MAX_BPF_ATTACH_TYPE
};

2
kernel/bpf/btf.c
View File

@ -6219,6 +6219,7 @@ static int btf_validate_prog_ctx_type(struct bpf_verifier_log *log, const struct
case BPF_TRACE_FENTRY:
case BPF_TRACE_FEXIT:
case BPF_MODIFY_RETURN:
case BPF_TRACE_FSESSION:
/* allow u64* as ctx */
if (btf_is_int(t) && t->size == 8)
return 0;
@ -6820,6 +6821,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
fallthrough;
case BPF_LSM_CGROUP:
case BPF_TRACE_FEXIT:
case BPF_TRACE_FSESSION:
/* When LSM programs are attached to void LSM hooks
* they use FEXIT trampolines and when attached to
* int LSM hooks, they use MODIFY_RETURN trampolines.

18
kernel/bpf/syscall.c
View File

@ -3577,6 +3577,7 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
case BPF_PROG_TYPE_TRACING:
if (prog->expected_attach_type != BPF_TRACE_FENTRY &&
prog->expected_attach_type != BPF_TRACE_FEXIT &&
prog->expected_attach_type != BPF_TRACE_FSESSION &&
prog->expected_attach_type != BPF_MODIFY_RETURN) {
err = -EINVAL;
goto out_put_prog;
@ -3626,7 +3627,21 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
key = bpf_trampoline_compute_key(tgt_prog, NULL, btf_id);
}
link = kzalloc(sizeof(*link), GFP_USER);
if (prog->expected_attach_type == BPF_TRACE_FSESSION) {
struct bpf_fsession_link *fslink;
fslink = kzalloc(sizeof(*fslink), GFP_USER);
if (fslink) {
bpf_link_init(&fslink->fexit.link, BPF_LINK_TYPE_TRACING,
&bpf_tracing_link_lops, prog, attach_type);
fslink->fexit.cookie = bpf_cookie;
link = &fslink->link;
} else {
link = NULL;
}
} else {
link = kzalloc(sizeof(*link), GFP_USER);
}
if (!link) {
err = -ENOMEM;
goto out_put_prog;
@ -4350,6 +4365,7 @@ attach_type_to_prog_type(enum bpf_attach_type attach_type)
case BPF_TRACE_RAW_TP:
case BPF_TRACE_FENTRY:
case BPF_TRACE_FEXIT:
case BPF_TRACE_FSESSION:
case BPF_MODIFY_RETURN:
return BPF_PROG_TYPE_TRACING;
case BPF_LSM_MAC:

53
kernel/bpf/trampoline.c
View File

@ -109,10 +109,17 @@ bool bpf_prog_has_trampoline(const struct bpf_prog *prog)
enum bpf_attach_type eatype = prog->expected_attach_type;
enum bpf_prog_type ptype = prog->type;
return (ptype == BPF_PROG_TYPE_TRACING &&
(eatype == BPF_TRACE_FENTRY || eatype == BPF_TRACE_FEXIT ||
eatype == BPF_MODIFY_RETURN)) ||
(ptype == BPF_PROG_TYPE_LSM && eatype == BPF_LSM_MAC);
switch (ptype) {
case BPF_PROG_TYPE_TRACING:
if (eatype == BPF_TRACE_FENTRY || eatype == BPF_TRACE_FEXIT ||
eatype == BPF_MODIFY_RETURN || eatype == BPF_TRACE_FSESSION)
return true;
return false;
case BPF_PROG_TYPE_LSM:
return eatype == BPF_LSM_MAC;
default:
return false;
}
}
void bpf_image_ksym_init(void *data, unsigned int size, struct bpf_ksym *ksym)
@ -559,6 +566,8 @@ static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
return BPF_TRAMP_MODIFY_RETURN;
case BPF_TRACE_FEXIT:
return BPF_TRAMP_FEXIT;
case BPF_TRACE_FSESSION:
return BPF_TRAMP_FSESSION;
case BPF_LSM_MAC:
if (!prog->aux->attach_func_proto->type)
/* The function returns void, we cannot modify its
@ -594,8 +603,10 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link,
struct bpf_trampoline *tr,
struct bpf_prog *tgt_prog)
{
struct bpf_fsession_link *fslink = NULL;
enum bpf_tramp_prog_type kind;
struct bpf_tramp_link *link_exiting;
struct hlist_head *prog_list;
int err = 0;
int cnt = 0, i;
@ -621,24 +632,43 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link,
BPF_MOD_JUMP, NULL,
link->link.prog->bpf_func);
}
if (kind == BPF_TRAMP_FSESSION) {
prog_list = &tr->progs_hlist[BPF_TRAMP_FENTRY];
cnt++;
} else {
prog_list = &tr->progs_hlist[kind];
}
if (cnt >= BPF_MAX_TRAMP_LINKS)
return -E2BIG;
if (!hlist_unhashed(&link->tramp_hlist))
/* prog already linked */
return -EBUSY;
hlist_for_each_entry(link_exiting, &tr->progs_hlist[kind], tramp_hlist) {
hlist_for_each_entry(link_exiting, prog_list, tramp_hlist) {
if (link_exiting->link.prog != link->link.prog)
continue;
/* prog already linked */
return -EBUSY;
}
hlist_add_head(&link->tramp_hlist, &tr->progs_hlist[kind]);
tr->progs_cnt[kind]++;
hlist_add_head(&link->tramp_hlist, prog_list);
if (kind == BPF_TRAMP_FSESSION) {
tr->progs_cnt[BPF_TRAMP_FENTRY]++;
fslink = container_of(link, struct bpf_fsession_link, link.link);
hlist_add_head(&fslink->fexit.tramp_hlist, &tr->progs_hlist[BPF_TRAMP_FEXIT]);
tr->progs_cnt[BPF_TRAMP_FEXIT]++;
} else {
tr->progs_cnt[kind]++;
}
err = bpf_trampoline_update(tr, true /* lock_direct_mutex */);
if (err) {
hlist_del_init(&link->tramp_hlist);
tr->progs_cnt[kind]--;
if (kind == BPF_TRAMP_FSESSION) {
tr->progs_cnt[BPF_TRAMP_FENTRY]--;
hlist_del_init(&fslink->fexit.tramp_hlist);
tr->progs_cnt[BPF_TRAMP_FEXIT]--;
} else {
tr->progs_cnt[kind]--;
}
}
return err;
}
@ -672,6 +702,13 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
guard(mutex)(&tgt_prog->aux->ext_mutex);
tgt_prog->aux->is_extended = false;
return err;
} else if (kind == BPF_TRAMP_FSESSION) {
struct bpf_fsession_link *fslink =
container_of(link, struct bpf_fsession_link, link.link);
hlist_del_init(&fslink->fexit.tramp_hlist);
tr->progs_cnt[BPF_TRAMP_FEXIT]--;
kind = BPF_TRAMP_FENTRY;
}
hlist_del_init(&link->tramp_hlist);
tr->progs_cnt[kind]--;

12
kernel/bpf/verifier.c
View File

@ -17848,6 +17848,7 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
switch (env->prog->expected_attach_type) {
case BPF_TRACE_FENTRY:
case BPF_TRACE_FEXIT:
case BPF_TRACE_FSESSION:
range = retval_range(0, 0);
break;
case BPF_TRACE_RAW_TP:
@ -23774,6 +23775,7 @@ patch_map_ops_generic:
if (prog_type == BPF_PROG_TYPE_TRACING &&
insn->imm == BPF_FUNC_get_func_ret) {
if (eatype == BPF_TRACE_FEXIT ||
eatype == BPF_TRACE_FSESSION ||
eatype == BPF_MODIFY_RETURN) {
/* Load nr_args from ctx - 8 */
insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
@ -24725,7 +24727,8 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
if (tgt_prog->type == BPF_PROG_TYPE_TRACING &&
prog_extension &&
(tgt_prog->expected_attach_type == BPF_TRACE_FENTRY ||
tgt_prog->expected_attach_type == BPF_TRACE_FEXIT)) {
tgt_prog->expected_attach_type == BPF_TRACE_FEXIT ||
tgt_prog->expected_attach_type == BPF_TRACE_FSESSION)) {
/* Program extensions can extend all program types
* except fentry/fexit. The reason is the following.
* The fentry/fexit programs are used for performance
@ -24740,7 +24743,7 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
* beyond reasonable stack size. Hence extending fentry
* is not allowed.
*/
bpf_log(log, "Cannot extend fentry/fexit\n");
bpf_log(log, "Cannot extend fentry/fexit/fsession\n");
return -EINVAL;
}
} else {
@ -24824,6 +24827,7 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
case BPF_LSM_CGROUP:
case BPF_TRACE_FENTRY:
case BPF_TRACE_FEXIT:
case BPF_TRACE_FSESSION:
if (!btf_type_is_func(t)) {
bpf_log(log, "attach_btf_id %u is not a function\n",
btf_id);
@ -24990,6 +24994,7 @@ static bool can_be_sleepable(struct bpf_prog *prog)
case BPF_TRACE_FEXIT:
case BPF_MODIFY_RETURN:
case BPF_TRACE_ITER:
case BPF_TRACE_FSESSION:
return true;
default:
return false;
@ -25071,9 +25076,10 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
tgt_info.tgt_name);
return -EINVAL;
} else if ((prog->expected_attach_type == BPF_TRACE_FEXIT ||
prog->expected_attach_type == BPF_TRACE_FSESSION ||
prog->expected_attach_type == BPF_MODIFY_RETURN) &&
btf_id_set_contains(&noreturn_deny, btf_id)) {
verbose(env, "Attaching fexit/fmod_ret to __noreturn function '%s' is rejected.\n",
verbose(env, "Attaching fexit/fsession/fmod_ret to __noreturn function '%s' is rejected.\n",
tgt_info.tgt_name);
return -EINVAL;
}

1
net/bpf/test_run.c
View File

@ -685,6 +685,7 @@ int bpf_prog_test_run_tracing(struct bpf_prog *prog,
switch (prog->expected_attach_type) {
case BPF_TRACE_FENTRY:
case BPF_TRACE_FEXIT:
case BPF_TRACE_FSESSION:
if (bpf_fentry_test1(1) != 2 ||
bpf_fentry_test2(2, 3) != 5 ||
bpf_fentry_test3(4, 5, 6) != 15 ||

1
net/core/bpf_sk_storage.c
View File

@ -365,6 +365,7 @@ static bool bpf_sk_storage_tracing_allowed(const struct bpf_prog *prog)
return true;
case BPF_TRACE_FENTRY:
case BPF_TRACE_FEXIT:
case BPF_TRACE_FSESSION:
return !!strncmp(prog->aux->attach_func_name, "bpf_sk_storage",
strlen("bpf_sk_storage"));
default:

1
tools/include/uapi/linux/bpf.h
View File

@ -1145,6 +1145,7 @@ enum bpf_attach_type {
BPF_NETKIT_PEER,
BPF_TRACE_KPROBE_SESSION,
BPF_TRACE_UPROBE_SESSION,
BPF_TRACE_FSESSION,
__MAX_BPF_ATTACH_TYPE
};

2
tools/testing/selftests/bpf/prog_tests/tracing_failure.c
View File

@ -73,7 +73,7 @@ static void test_tracing_deny(void)
static void test_fexit_noreturns(void)
{
test_tracing_fail_prog("fexit_noreturns",
"Attaching fexit/fmod_ret to __noreturn function 'do_exit' is rejected.");
"Attaching fexit/fsession/fmod_ret to __noreturn function 'do_exit' is rejected.");
}
void test_tracing_failure(void)