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Message-ID: <20251026030143.23807-3-dongml2@chinatelecom.cn>
Date: Sun, 26 Oct 2025 11:01:38 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: ast@...nel.org,
jolsa@...nel.org
Cc: daniel@...earbox.net,
john.fastabend@...il.com,
andrii@...nel.org,
martin.lau@...ux.dev,
eddyz87@...il.com,
song@...nel.org,
yonghong.song@...ux.dev,
kpsingh@...nel.org,
sdf@...ichev.me,
haoluo@...gle.com,
mattbobrowski@...gle.com,
rostedt@...dmis.org,
mhiramat@...nel.org,
leon.hwang@...ux.dev,
jiang.biao@...ux.dev,
bpf@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org
Subject: [PATCH bpf-next v3 2/7] bpf: add two kfunc for TRACE_SESSION
If TRACE_SESSION exists, we will use extra 8-bytes in the stack of the
trampoline to store the flags that we needed, and the 8-bytes lie after
the return value, which means ctx[nr_args + 1]. And we will store the
flag "is_exit" to the first bit of it.
Introduce the kfunc bpf_tracing_is_exit(), which is used to tell if it
is fexit currently. Meanwhile, inline it in the verifier.
Add the kfunc bpf_fsession_cookie(), which is similar to
bpf_session_cookie() and return the address of the session cookie. The
address of the session cookie is stored after session flags, which means
ctx[nr_args + 2]. Inline this kfunc in the verifier too.
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>
---
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 | 1 +
kernel/bpf/verifier.c | 33 ++++++++++++++++++++--
kernel/trace/bpf_trace.c | 59 ++++++++++++++++++++++++++++++++++++++--
3 files changed, 88 insertions(+), 5 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 6b5855c80fa6..ce55d3881c0d 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1736,6 +1736,7 @@ struct bpf_prog {
enforce_expected_attach_type:1, /* Enforce expected_attach_type checking at attach time */
call_get_stack:1, /* Do we call bpf_get_stack() or bpf_get_stackid() */
call_get_func_ip:1, /* Do we call get_func_ip() */
+ call_session_cookie:1, /* Do we call bpf_fsession_cookie() */
tstamp_type_access:1, /* Accessed __sk_buff->tstamp_type */
sleepable:1; /* BPF program is sleepable */
enum bpf_prog_type type; /* Type of BPF program */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 818deb6a06e4..6f8aa4718d6f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12293,6 +12293,8 @@ enum special_kfunc_type {
KF___bpf_trap,
KF_bpf_task_work_schedule_signal,
KF_bpf_task_work_schedule_resume,
+ KF_bpf_tracing_is_exit,
+ KF_bpf_fsession_cookie,
};
BTF_ID_LIST(special_kfunc_list)
@@ -12365,6 +12367,8 @@ BTF_ID(func, bpf_res_spin_unlock_irqrestore)
BTF_ID(func, __bpf_trap)
BTF_ID(func, bpf_task_work_schedule_signal)
BTF_ID(func, bpf_task_work_schedule_resume)
+BTF_ID(func, bpf_tracing_is_exit)
+BTF_ID(func, bpf_fsession_cookie)
static bool is_task_work_add_kfunc(u32 func_id)
{
@@ -12419,7 +12423,9 @@ 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_tracing_is_exit] ||
+ meta->func_id == special_kfunc_list[KF_bpf_fsession_cookie])
return KF_ARG_PTR_TO_CTX;
/* In this function, we verify the kfunc's BTF as per the argument type,
@@ -13912,7 +13918,8 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
}
}
- if (meta.func_id == special_kfunc_list[KF_bpf_session_cookie]) {
+ if (meta.func_id == special_kfunc_list[KF_bpf_session_cookie] ||
+ meta.func_id == special_kfunc_list[KF_bpf_fsession_cookie]) {
meta.r0_size = sizeof(u64);
meta.r0_rdonly = false;
}
@@ -14193,6 +14200,9 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
return err;
}
+ if (meta.func_id == special_kfunc_list[KF_bpf_fsession_cookie])
+ env->prog->call_session_cookie = true;
+
return 0;
}
@@ -22012,6 +22022,25 @@ 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_tracing_is_exit]) {
+ /* Load nr_args from ctx - 8 */
+ insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
+ /* add rax, 1 */
+ insn_buf[1] = BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 1);
+ insn_buf[2] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3);
+ insn_buf[3] = BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1);
+ insn_buf[4] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
+ insn_buf[5] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 1);
+ *cnt = 6;
+ } else if (desc->func_id == special_kfunc_list[KF_bpf_fsession_cookie]) {
+ /* Load nr_args from ctx - 8 */
+ insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
+ /* add rax, 2 */
+ insn_buf[1] = BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 2);
+ insn_buf[2] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3);
+ insn_buf[3] = BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1);
+ insn_buf[4] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
+ *cnt = 5;
}
if (env->insn_aux_data[insn_idx].arg_prog) {
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 4f87c16d915a..4a8568bd654d 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3356,12 +3356,65 @@ static const struct btf_kfunc_id_set bpf_kprobe_multi_kfunc_set = {
.filter = bpf_kprobe_multi_filter,
};
-static int __init bpf_kprobe_multi_kfuncs_init(void)
+__bpf_kfunc_start_defs();
+
+__bpf_kfunc bool bpf_tracing_is_exit(void *ctx)
{
- return register_btf_kfunc_id_set(BPF_PROG_TYPE_KPROBE, &bpf_kprobe_multi_kfunc_set);
+ /* This helper call is inlined by verifier. */
+ u64 nr_args = ((u64 *)ctx)[-1];
+
+ /*
+ * ctx[nr_args + 1] is the session flags, and the last bit is
+ * is_exit.
+ */
+ return ((u64 *)ctx)[nr_args + 1] & 1;
+}
+
+__bpf_kfunc u64 *bpf_fsession_cookie(void *ctx)
+{
+ /* This helper call is inlined by verifier. */
+ u64 nr_args = ((u64 *)ctx)[-1];
+
+ /* ctx[nr_args + 2] is the session cookie address */
+ return (u64 *)((u64 *)ctx)[nr_args + 2];
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(tracing_kfunc_set_ids)
+BTF_ID_FLAGS(func, bpf_tracing_is_exit, KF_FASTCALL)
+BTF_ID_FLAGS(func, bpf_fsession_cookie, KF_FASTCALL)
+BTF_KFUNCS_END(tracing_kfunc_set_ids)
+
+static int bpf_tracing_filter(const struct bpf_prog *prog, u32 kfunc_id)
+{
+ if (!btf_id_set8_contains(&tracing_kfunc_set_ids, kfunc_id))
+ return 0;
+
+ if (prog->type != BPF_PROG_TYPE_TRACING ||
+ prog->expected_attach_type != BPF_TRACE_SESSION)
+ return -EINVAL;
+
+ return 0;
+}
+
+static const struct btf_kfunc_id_set bpf_tracing_kfunc_set = {
+ .owner = THIS_MODULE,
+ .set = &tracing_kfunc_set_ids,
+ .filter = bpf_tracing_filter,
+};
+
+static int __init bpf_trace_kfuncs_init(void)
+{
+ int err = 0;
+
+ err = err ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_KPROBE, &bpf_kprobe_multi_kfunc_set);
+ err = err ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_tracing_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);
--
2.51.1
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