[PATCH v2 bpf 3/3] selftests/bpf: Add tests for livepatch + bpf trampoline
From: Song Liu <song@kernel.org>
Date: 2025-10-24 18:29:23
Also in:
bpf, live-patching
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [selftests] (test runners & infrastructure), kernel selftest framework, the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Shuah Khan, Linus Torvalds
Both livepatch and BPF trampoline use ftrace. Special attention is needed
when livepatch and fexit program touch the same function at the same
time, because livepatch updates a kernel function and the BPF trampoline
need to call into the right version of the kernel function.
Use samples/livepatch/livepatch-sample.ko for the test.
The test covers two cases:
1) When a fentry program is loaded first. This exercises the
modify_ftrace_direct code path.
2) When a fentry program is loaded first. This exercises the
register_ftrace_direct code path.
Signed-off-by: Song Liu <song@kernel.org>
---
tools/testing/selftests/bpf/config | 3 +
.../bpf/prog_tests/livepatch_trampoline.c | 107 ++++++++++++++++++
.../bpf/progs/livepatch_trampoline.c | 30 +++++
3 files changed, 140 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/livepatch_trampoline.c
create mode 100644 tools/testing/selftests/bpf/progs/livepatch_trampoline.c
diff --git a/tools/testing/selftests/bpf/config b/tools/testing/selftests/bpf/config
index 70b28c1e653e..f2a2fd236ca8 100644
--- a/tools/testing/selftests/bpf/config
+++ b/tools/testing/selftests/bpf/config@@ -50,6 +50,7 @@ CONFIG_IPV6_SIT=y CONFIG_IPV6_TUNNEL=y CONFIG_KEYS=y CONFIG_LIRC=y +CONFIG_LIVEPATCH=y CONFIG_LWTUNNEL=y CONFIG_MODULE_SIG=y CONFIG_MODULE_SRCVERSION_ALL=y
@@ -111,6 +112,8 @@ CONFIG_IP6_NF_FILTER=y CONFIG_NF_NAT=y CONFIG_PACKET=y CONFIG_RC_CORE=y +CONFIG_SAMPLES=y +CONFIG_SAMPLE_LIVEPATCH=m CONFIG_SECURITY=y CONFIG_SECURITYFS=y CONFIG_SYN_COOKIES=y
diff --git a/tools/testing/selftests/bpf/prog_tests/livepatch_trampoline.c b/tools/testing/selftests/bpf/prog_tests/livepatch_trampoline.c
new file mode 100644
index 000000000000..72aa5376c30e
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/livepatch_trampoline.c@@ -0,0 +1,107 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */ + +#include <test_progs.h> +#include "testing_helpers.h" +#include "livepatch_trampoline.skel.h" + +static int load_livepatch(void) +{ + char path[4096]; + + /* CI will set KBUILD_OUTPUT */ + snprintf(path, sizeof(path), "%s/samples/livepatch/livepatch-sample.ko", + getenv("KBUILD_OUTPUT") ? : "../../../.."); + + return load_module(path, env_verbosity > VERBOSE_NONE); +} + +static void unload_livepatch(void) +{ + /* Disable the livepatch before unloading the module */ + system("echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled"); + + unload_module("livepatch_sample", env_verbosity > VERBOSE_NONE); +} + +static void read_proc_cmdline(void) +{ + char buf[4096]; + int fd, ret; + + fd = open("/proc/cmdline", O_RDONLY); + if (!ASSERT_OK_FD(fd, "open /proc/cmdline")) + return; + + ret = read(fd, buf, sizeof(buf)); + if (!ASSERT_GT(ret, 0, "read /proc/cmdline")) + goto out; + + ASSERT_OK(strncmp(buf, "this has been live patched", 26), "strncmp"); + +out: + close(fd); +} + +static void __test_livepatch_trampoline(bool fexit_first) +{ + struct livepatch_trampoline *skel = NULL; + int err; + + skel = livepatch_trampoline__open_and_load(); + if (!ASSERT_OK_PTR(skel, "skel_open_and_load")) + goto out; + + skel->bss->my_pid = getpid(); + + if (!fexit_first) { + /* fentry program is loaded first by default */ + err = livepatch_trampoline__attach(skel); + if (!ASSERT_OK(err, "skel_attach")) + goto out; + } else { + /* Manually load fexit program first. */ + skel->links.fexit_cmdline = bpf_program__attach(skel->progs.fexit_cmdline); + if (!ASSERT_OK_PTR(skel->links.fexit_cmdline, "attach_fexit")) + goto out; + + skel->links.fentry_cmdline = bpf_program__attach(skel->progs.fentry_cmdline); + if (!ASSERT_OK_PTR(skel->links.fentry_cmdline, "attach_fentry")) + goto out; + } + + read_proc_cmdline(); + + ASSERT_EQ(skel->bss->fentry_hit, 1, "fentry_hit"); + ASSERT_EQ(skel->bss->fexit_hit, 1, "fexit_hit"); +out: + livepatch_trampoline__destroy(skel); +} + +void test_livepatch_trampoline(void) +{ + int retry_cnt = 0; + +retry: + if (load_livepatch()) { + if (retry_cnt) { + ASSERT_OK(1, "load_livepatch"); + goto out; + } + /* + * Something else (previous run of the same test?) loaded + * the KLP module. Unload the KLP module and retry. + */ + unload_livepatch(); + retry_cnt++; + goto retry; + } + + if (test__start_subtest("fentry_first")) + __test_livepatch_trampoline(false); + + if (test__start_subtest("fexit_first")) + __test_livepatch_trampoline(true); +out: + unload_livepatch(); +}
diff --git a/tools/testing/selftests/bpf/progs/livepatch_trampoline.c b/tools/testing/selftests/bpf/progs/livepatch_trampoline.c
new file mode 100644
index 000000000000..15579d5bcd91
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/livepatch_trampoline.c@@ -0,0 +1,30 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */ + +#include <linux/bpf.h> +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_tracing.h> + +int fentry_hit; +int fexit_hit; +int my_pid; + +SEC("fentry/cmdline_proc_show") +int BPF_PROG(fentry_cmdline) +{ + if (my_pid != (bpf_get_current_pid_tgid() >> 32)) + return 0; + + fentry_hit = 1; + return 0; +} + +SEC("fexit/cmdline_proc_show") +int BPF_PROG(fexit_cmdline) +{ + if (my_pid != (bpf_get_current_pid_tgid() >> 32)) + return 0; + + fexit_hit = 1; + return 0; +}
--
2.47.3