selftests/bpf: Add tests for livepatch + bpf trampoline

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>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20251027175023.1521602-4-song@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/tools/testing/selftests/bpf/config b/tools/testing/selftests/bpf/config
index 70b28c1e653eadb19de1ee869b62a67098837109..f2a2fd236ca839bb430fde18b65d2f4930f110c9 100644 (file)
--- 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 (file)
index 0000000..72aa537
--- /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 (file)
index 0000000..15579d5
--- /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;
+}