kho: add test for kexec handover

Testing kexec handover requires a kernel driver that will generate some
data and preserve it with KHO on the first boot and then restore that data
and verify it was preserved properly after kexec.

To facilitate such test, along with the kernel driver responsible for data
generation, preservation and restoration add a script that runs a kernel
in a VM with a minimal /init.  The /init enables KHO, loads a kernel image
for kexec and runs kexec reboot.  After the boot of the kexeced kernel,
the driver verifies that the data was properly preserved.

[rppt@kernel.org: fix section mismatch]
  Link: https://lkml.kernel.org/r/aIiRC8fXiOXKbPM_@kernel.org
Link: https://lkml.kernel.org/r/20250727083733.2590139-1-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 100 insertions, 0 deletions

diff --git a/tools/testing/selftests/kho/init.c b/tools/testing/selftests/kho/init.c
new file mode 100644
index 000000000000..8034e24c6bf6
--- /dev/null
+++ b/tools/testing/selftests/kho/init.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#ifndef NOLIBC
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <syscall.h>
+#include <sys/mount.h>
+#include <sys/reboot.h>
+#endif
+
+/* from arch/x86/include/asm/setup.h */
+#define COMMAND_LINE_SIZE	2048
+
+/* from include/linux/kexex.h */
+#define KEXEC_FILE_NO_INITRAMFS	0x00000004
+
+#define KHO_FINILIZE "/debugfs/kho/out/finalize"
+#define KERNEL_IMAGE "/kernel"
+
+static int mount_filesystems(void)
+{
+	if (mount("debugfs", "/debugfs", "debugfs", 0, NULL) < 0)
+		return -1;
+
+	return mount("proc", "/proc", "proc", 0, NULL);
+}
+
+static int kho_enable(void)
+{
+	const char enable[] = "1";
+	int fd;
+
+	fd = open(KHO_FINILIZE, O_RDWR);
+	if (fd < 0)
+		return -1;
+
+	if (write(fd, enable, sizeof(enable)) != sizeof(enable))
+		return 1;
+
+	close(fd);
+	return 0;
+}
+
+static long kexec_file_load(int kernel_fd, int initrd_fd,
+			    unsigned long cmdline_len, const char *cmdline,
+			    unsigned long flags)
+{
+	return syscall(__NR_kexec_file_load, kernel_fd, initrd_fd, cmdline_len,
+		       cmdline, flags);
+}
+
+static int kexec_load(void)
+{
+	char cmdline[COMMAND_LINE_SIZE];
+	ssize_t len;
+	int fd, err;
+
+	fd = open("/proc/cmdline", O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	len = read(fd, cmdline, sizeof(cmdline));
+	close(fd);
+	if (len < 0)
+		return -1;
+
+	/* replace \n with \0 */
+	cmdline[len - 1] = 0;
+	fd = open(KERNEL_IMAGE, O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	err = kexec_file_load(fd, -1, len, cmdline, KEXEC_FILE_NO_INITRAMFS);
+	close(fd);
+
+	return err ? : 0;
+}
+
+int main(int argc, char *argv[])
+{
+	if (mount_filesystems())
+		goto err_reboot;
+
+	if (kho_enable())
+		goto err_reboot;
+
+	if (kexec_load())
+		goto err_reboot;
+
+	if (reboot(RB_KEXEC))
+		goto err_reboot;
+
+	return 0;
+
+err_reboot:
+	reboot(RB_AUTOBOOT);
+	return -1;
+}