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Message-ID: <20260107064352.291069-5-dongml2@chinatelecom.cn>
Date: Wed, 7 Jan 2026 14:43:45 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: ast@...nel.org,
andrii@...nel.org
Cc: daniel@...earbox.net,
martin.lau@...ux.dev,
eddyz87@...il.com,
song@...nel.org,
yonghong.song@...ux.dev,
john.fastabend@...il.com,
kpsingh@...nel.org,
sdf@...ichev.me,
haoluo@...gle.com,
jolsa@...nel.org,
davem@...emloft.net,
dsahern@...nel.org,
tglx@...utronix.de,
mingo@...hat.com,
jiang.biao@...ux.dev,
bp@...en8.de,
dave.hansen@...ux.intel.com,
x86@...nel.org,
hpa@...or.com,
bpf@...r.kernel.org,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next v7 04/11] bpf: support fsession for bpf_session_is_return
If fsession exists, we will use the bit (1 << BPF_TRAMP_M_IS_RETURN) in
ctx[-1] to store the "is_return" flag.
Introduce the function bpf_fsession_is_return(), which is used to tell if
it is fexit currently. Meanwhile, inline it in the verifier. The calling
to bpf_session_is_return() will be changed to bpf_fsession_is_return() in
verifier for fsession.
Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
Co-developed-by: Leon Hwang <leon.hwang@...ux.dev>
Signed-off-by: Leon Hwang <leon.hwang@...ux.dev>
---
v7:
- reuse the kfunc bpf_session_is_return() instead of introduce new kfunc
v4:
- split out the bpf_fsession_cookie() to another patch
v3:
- merge the bpf_tracing_is_exit and bpf_fsession_cookie into a single
patch
v2:
- store the session flags after return value, instead of before nr_args
- inline the bpf_tracing_is_exit, as Jiri suggested
---
include/linux/bpf.h | 5 +++++
kernel/bpf/verifier.c | 15 ++++++++++++++-
kernel/trace/bpf_trace.c | 34 +++++++++++++++++++++++-----------
3 files changed, 42 insertions(+), 12 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 565ca7052518..d996dd390681 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1229,6 +1229,9 @@ enum {
#endif
};
+#define BPF_TRAMP_M_NR_ARGS 0
+#define BPF_TRAMP_M_IS_RETURN 8
+
struct bpf_tramp_links {
struct bpf_tramp_link *links[BPF_MAX_TRAMP_LINKS];
int nr_links;
@@ -3945,4 +3948,6 @@ static inline int bpf_map_check_op_flags(struct bpf_map *map, u64 flags, u64 all
return 0;
}
+bool bpf_fsession_is_return(void *ctx);
+
#endif /* _LINUX_BPF_H */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index bfff3f84fd91..d3709edd0e51 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12374,6 +12374,7 @@ enum special_kfunc_type {
KF_bpf_arena_alloc_pages,
KF_bpf_arena_free_pages,
KF_bpf_arena_reserve_pages,
+ KF_bpf_session_is_return,
};
BTF_ID_LIST(special_kfunc_list)
@@ -12451,6 +12452,7 @@ BTF_ID(func, bpf_task_work_schedule_resume_impl)
BTF_ID(func, bpf_arena_alloc_pages)
BTF_ID(func, bpf_arena_free_pages)
BTF_ID(func, bpf_arena_reserve_pages)
+BTF_ID(func, bpf_session_is_return)
static bool is_task_work_add_kfunc(u32 func_id)
{
@@ -12505,7 +12507,8 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
struct bpf_reg_state *reg = ®s[regno];
bool arg_mem_size = false;
- if (meta->func_id == special_kfunc_list[KF_bpf_cast_to_kern_ctx])
+ if (meta->func_id == special_kfunc_list[KF_bpf_cast_to_kern_ctx] ||
+ meta->func_id == special_kfunc_list[KF_bpf_session_is_return])
return KF_ARG_PTR_TO_CTX;
if (argno + 1 < nargs &&
@@ -22440,6 +22443,9 @@ static int specialize_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_desc
} else if (func_id == special_kfunc_list[KF_bpf_arena_free_pages]) {
if (env->insn_aux_data[insn_idx].non_sleepable)
addr = (unsigned long)bpf_arena_free_pages_non_sleepable;
+ } else if (func_id == special_kfunc_list[KF_bpf_session_is_return]) {
+ if (prog->expected_attach_type == BPF_TRACE_FSESSION)
+ addr = (unsigned long)bpf_fsession_is_return;
}
desc->addr = addr;
return 0;
@@ -22558,6 +22564,13 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
desc->func_id == special_kfunc_list[KF_bpf_rdonly_cast]) {
insn_buf[0] = BPF_MOV64_REG(BPF_REG_0, BPF_REG_1);
*cnt = 1;
+ } else if (desc->func_id == special_kfunc_list[KF_bpf_session_is_return] &&
+ env->prog->expected_attach_type == BPF_TRACE_FSESSION) {
+ /* Load nr_args from ctx - 8 */
+ insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
+ insn_buf[1] = BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, BPF_TRAMP_M_IS_RETURN);
+ insn_buf[2] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 1);
+ *cnt = 3;
}
if (env->insn_aux_data[insn_idx].arg_prog) {
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 736b32cf2195..9d3bf3bbe8f6 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3314,6 +3314,12 @@ static u64 bpf_uprobe_multi_entry_ip(struct bpf_run_ctx *ctx)
}
#endif /* CONFIG_UPROBES */
+bool bpf_fsession_is_return(void *ctx)
+{
+ /* This helper call is inlined by verifier. */
+ return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_RETURN));
+}
+
__bpf_kfunc_start_defs();
__bpf_kfunc bool bpf_session_is_return(void *ctx)
@@ -3334,34 +3340,40 @@ __bpf_kfunc __u64 *bpf_session_cookie(void *ctx)
__bpf_kfunc_end_defs();
-BTF_KFUNCS_START(kprobe_multi_kfunc_set_ids)
+BTF_KFUNCS_START(session_kfunc_set_ids)
BTF_ID_FLAGS(func, bpf_session_is_return)
BTF_ID_FLAGS(func, bpf_session_cookie)
-BTF_KFUNCS_END(kprobe_multi_kfunc_set_ids)
+BTF_KFUNCS_END(session_kfunc_set_ids)
-static int bpf_kprobe_multi_filter(const struct bpf_prog *prog, u32 kfunc_id)
+static int bpf_session_filter(const struct bpf_prog *prog, u32 kfunc_id)
{
- if (!btf_id_set8_contains(&kprobe_multi_kfunc_set_ids, kfunc_id))
+ if (!btf_id_set8_contains(&session_kfunc_set_ids, kfunc_id))
return 0;
- if (!is_kprobe_session(prog) && !is_uprobe_session(prog))
+ if (!is_kprobe_session(prog) && !is_uprobe_session(prog) &&
+ prog->expected_attach_type != BPF_TRACE_FSESSION)
return -EACCES;
return 0;
}
-static const struct btf_kfunc_id_set bpf_kprobe_multi_kfunc_set = {
+static const struct btf_kfunc_id_set bpf_session_kfunc_set = {
.owner = THIS_MODULE,
- .set = &kprobe_multi_kfunc_set_ids,
- .filter = bpf_kprobe_multi_filter,
+ .set = &session_kfunc_set_ids,
+ .filter = bpf_session_filter,
};
-static int __init bpf_kprobe_multi_kfuncs_init(void)
+static int __init bpf_trace_kfuncs_init(void)
{
- return register_btf_kfunc_id_set(BPF_PROG_TYPE_KPROBE, &bpf_kprobe_multi_kfunc_set);
+ int err = 0;
+
+ err = err ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_KPROBE, &bpf_session_kfunc_set);
+ err = err ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_session_kfunc_set);
+
+ return err;
}
-late_initcall(bpf_kprobe_multi_kfuncs_init);
+late_initcall(bpf_trace_kfuncs_init);
typedef int (*copy_fn_t)(void *dst, const void *src, u32 size, struct task_struct *tsk);
--
2.52.0
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