bpf: add tracing session support

image-dragon · Kernel Patches Daemon · commit 6677ab1c8e05 · 2025-10-28T09:04:15.000-07:00
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 &lt;dongml2@chinatelecom.cn&gt;
Co-developed-by: Leon Hwang &lt;leon.hwang@linux.dev&gt;
Signed-off-by: Leon Hwang &lt;leon.hwang@linux.dev&gt;
diff --git 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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -1276,6 +1276,7 @@ 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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -17291,6 +17291,7 @@ 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;
@@ -22783,6 +22784,7 @@ 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);
@@ -23724,7 +23726,8 @@ 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
@@ -23739,7 +23742,7 @@ 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 {
@@ -23823,6 +23826,7 @@ 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);
@@ -23989,6 +23993,7 @@ 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;
@@ -24070,9 +24075,10 @@ 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
@@ -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
@@ -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
@@ -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
@@ -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)
