[PATCH bpf-next v2 01/10] bpf: add tracing session support

Menglong Dong
2025-10-22T08:02:15Z

The tracing session 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.

While a non-zero value is returned by the fentry, the fexit will be
skipped, which is similar to kprobe session.

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>
---
arch/arm64/net/bpf_jit_comp.c | 3 +++
arch/loongarch/net/bpf_jit.c | 3 +++
arch/powerpc/net/bpf_jit_comp.c | 3 +++
arch/riscv/net/bpf_jit_comp64.c | 3 +++
arch/s390/net/bpf_jit_comp.c | 3 +++
arch/x86/net/bpf_jit_comp.c | 3 +++
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 1 +
kernel/bpf/btf.c | 2 ++
kernel/bpf/syscall.c | 2 ++
kernel/bpf/trampoline.c | 5 ++++-
kernel/bpf/verifier.c | 12 +++++++++---
net/bpf/test_run.c | 1 +
net/core/bpf_sk_storage.c | 1 +
tools/include/uapi/linux/bpf.h | 1 +
.../selftests/bpf/prog_tests/tracing_failure.c | 2 +-
16 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index ab83089c3d8f..06f4bd6c6755 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -2788,6 +2788,9 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *ro_image,
void *image, *tmp;
int ret;

+ if (tlinks[BPF_TRAMP_SESSION].nr_links)
+ return -EOPNOTSUPP;
+
/* image doesn't need to be in module memory range, so we can
* use kvmalloc.
*/
diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index cbe53d0b7fb0..ad596341658a 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -1739,6 +1739,9 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *ro_image,
void *image, *tmp;
struct jit_ctx ctx;

+ if (tlinks[BPF_TRAMP_SESSION].nr_links)
+ return -EOPNOTSUPP;
+
size = ro_image_end - ro_image;
image = kvmalloc(size, GFP_KERNEL);
if (!image)
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 88ad5ba7b87f..bcc0ce09f6fa 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -1017,6 +1017,9 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
void *rw_image, *tmp;
int ret;

+ if (tlinks[BPF_TRAMP_SESSION].nr_links)
+ return -EOPNOTSUPP;
+
/*
* rw_image doesn't need to be in module memory range, so we can
* use kvmalloc.
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 45cbc7c6fe49..55b0284bf177 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -1286,6 +1286,9 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *ro_image,
struct rv_jit_context ctx;
u32 size = ro_image_end - ro_image;

+ if (tlinks[BPF_TRAMP_SESSION].nr_links)
+ return -EOPNOTSUPP;
+
image = kvmalloc(size, GFP_KERNEL);
if (!image)
return -ENOMEM;
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index cf461d76e9da..3f25bf55b150 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -2924,6 +2924,9 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image,
struct bpf_tramp_jit tjit;
int ret;

+ if (tlinks[BPF_TRAMP_SESSION].nr_links)
+ return -EOPNOTSUPP;
+
/* Compute offsets, check whether the code fits. */
memset(&tjit, 0, sizeof(tjit));
ret = __arch_prepare_bpf_trampoline(im, &tjit, m, flags,
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index d4c93d9e73e4..389c3a96e2b8 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -3478,6 +3478,9 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
int ret;
u32 size = image_end - image;

+ if (tlinks[BPF_TRAMP_SESSION].nr_links)
+ return -EOPNOTSUPP;
+
/* rw_image doesn't need to be in module memory range, so we can
* use kvmalloc.
*/
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 204f9c759a41..3f6cad5df2db 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1270,6 +1270,7 @@ enum bpf_tramp_prog_type {
BPF_TRAMP_FENTRY,
BPF_TRAMP_FEXIT,
BPF_TRAMP_MODIFY_RETURN,
+ BPF_TRAMP_SESSION,
BPF_TRAMP_MAX,
BPF_TRAMP_REPLACE, /* more than MAX */
};
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 6829936d33f5..79ba3023e8be 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1133,6 +1133,7 @@ enum bpf_attach_type {
BPF_NETKIT_PEER,
BPF_TRACE_KPROBE_SESSION,
BPF_TRACE_UPROBE_SESSION,
+ BPF_TRACE_SESSION,
__MAX_BPF_ATTACH_TYPE
};

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 0de8fc8a0e0b..2c1c3e0caff8 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6107,6 +6107,7 @@ 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_SESSION:
/* allow u64* as ctx */
if (btf_is_int(t) && t->size == 8)
return 0;
@@ -6704,6 +6705,7 @@ 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_SESSION:
/* 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.
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8a129746bd6c..cb483701fe39 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3564,6 +3564,7 @@ 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_SESSION &&
prog->expected_attach_type != BPF_MODIFY_RETURN) {
err = -EINVAL;
goto out_put_prog;
@@ -4337,6 +4338,7 @@ 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_SESSION:
case BPF_MODIFY_RETURN:
return BPF_PROG_TYPE_TRACING;
case BPF_LSM_MAC:
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 5949095e51c3..f6d4dea3461e 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -111,7 +111,7 @@ bool bpf_prog_has_trampoline(const struct bpf_prog *prog)

return (ptype == BPF_PROG_TYPE_TRACING &&
(eatype == BPF_TRACE_FENTRY || eatype == BPF_TRACE_FEXIT ||
- eatype == BPF_MODIFY_RETURN)) ||
+ eatype == BPF_MODIFY_RETURN || eatype == BPF_TRACE_SESSION)) ||
(ptype == BPF_PROG_TYPE_LSM && eatype == BPF_LSM_MAC);
}

@@ -418,6 +418,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
tr->flags &= (BPF_TRAMP_F_SHARE_IPMODIFY | BPF_TRAMP_F_TAIL_CALL_CTX);

if (tlinks[BPF_TRAMP_FEXIT].nr_links ||
+ tlinks[BPF_TRAMP_SESSION].nr_links ||
tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links) {
/* NOTE: BPF_TRAMP_F_RESTORE_REGS and BPF_TRAMP_F_SKIP_FRAME
* should not be set together.
@@ -515,6 +516,8 @@ 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_SESSION:
+ return BPF_TRAMP_SESSION;
case BPF_LSM_MAC:
if (!prog->aux->attach_func_proto->type)
/* The function returns void, we cannot modify its
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9b4f6920f79b..3ffdf2143f16 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17281,6 +17281,7 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
break;
case BPF_TRACE_RAW_TP:
case BPF_MODIFY_RETURN:
+ case BPF_TRACE_SESSION:
return 0;
case BPF_TRACE_ITER:
break;
@@ -22736,6 +22737,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
if (prog_type == BPF_PROG_TYPE_TRACING &&
insn->imm == BPF_FUNC_get_func_ret) {
if (eatype == BPF_TRACE_FEXIT ||
+ eatype == BPF_TRACE_SESSION ||
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);
@@ -23677,7 +23679,8 @@ 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_SESSION)) {
/* Program extensions can extend all program types
* except fentry/fexit. The reason is the following.
* The fentry/fexit programs are used for performance
@@ -23692,7 +23695,7 @@ 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/session\n");
return -EINVAL;
}
} else {
@@ -23776,6 +23779,7 @@ 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_SESSION:
if (!btf_type_is_func(t)) {
bpf_log(log, "attach_btf_id %u is not a function\n",
btf_id);
@@ -23942,6 +23946,7 @@ static bool can_be_sleepable(struct bpf_prog *prog)
case BPF_TRACE_FEXIT:
case BPF_MODIFY_RETURN:
case BPF_TRACE_ITER:
+ case BPF_TRACE_SESSION:
return true;
default:
return false;
@@ -24023,9 +24028,10 @@ 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_SESSION ||
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/session/fmod_ret to __noreturn function '%s' is rejected.\n",
tgt_info.tgt_name);
return -EINVAL;
}
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 73d5f0d9f5f4..f7f0fd5383c4 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -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_SESSION:
if (bpf_fentry_test1(1) != 2 ||
bpf_fentry_test2(2, 3) != 5 ||
bpf_fentry_test3(4, 5, 6) != 15 ||
diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
index d3fbaf89a698..8da8834aa134 100644
--- a/net/core/bpf_sk_storage.c
+++ b/net/core/bpf_sk_storage.c
@@ -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_SESSION:
return !!strncmp(prog->aux->attach_func_name, "bpf_sk_storage",
strlen("bpf_sk_storage"));
default:
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 6829936d33f5..79ba3023e8be 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1133,6 +1133,7 @@ enum bpf_attach_type {
BPF_NETKIT_PEER,
BPF_TRACE_KPROBE_SESSION,
BPF_TRACE_UPROBE_SESSION,
+ BPF_TRACE_SESSION,
__MAX_BPF_ATTACH_TYPE
};

diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_failure.c b/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
index 10e231965589..58b02552507d 100644
--- a/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
+++ b/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
@@ -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/session/fmod_ret to __noreturn function 'do_exit' is rejected.");
}

void test_tracing_failure(void)
--
2.51.1.dirty