Merge branch 'fix-ftrace-for-livepatch-bpf-fexit-programs'

Song Liu says:

====================
Fix ftrace for livepatch + BPF fexit programs

livepatch and BPF trampoline are two special users of ftrace. livepatch
uses ftrace with IPMODIFY flag and BPF trampoline uses ftrace direct
functions. When livepatch and BPF trampoline with fexit programs attach to
the same kernel function, BPF trampoline needs to call into the patched
version of the kernel function.

1/3 and 2/3 of this patchset fix two issues with livepatch + fexit cases,
one in the register_ftrace_direct path, the other in the
modify_ftrace_direct path.

3/3 adds selftests for both cases.
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
v4: https://patch.msgid.link/20251027175023.1521602-1-song@kernel.org

Changes v3 => v4:
1. Add helper reset_direct. (Steven)
2. Add Reviewed-by from Jiri.
3. Fix minor typo in comments.

v3: https://lore.kernel.org/bpf/20251026205445.1639632-1-song@kernel.org/

Changes v2 => v3:
1. Incorporate feedback by AI, which also fixes build error reported by
   Steven and kernel test robot.

v2: https://lore.kernel.org/bpf/20251024182901.3247573-1-song@kernel.org/

Changes v1 => v2:
1. Target bpf tree. (Alexei)
2. Bring back the FTRACE_WARN_ON in __ftrace_hash_update_ipmodify
   for valid code paths. (Steven)
3. Update selftests with cleaner way to find livepatch-sample.ko.
   (offlline discussion with Ihor)

v1: https://lore.kernel.org/bpf/20251024071257.3956031-1-song@kernel.org/
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 140 insertions, 0 deletions

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;
+}