Implement kexec
To support ramdump of VMs, implement a kexec binary and add it to
Microdroid. The binary will be used to preload the kernel and the init
ramdisk that the system will boot into when a kernel panic occurs.
The binary is very minimal. It has much less functionalities than the
upstream kexec-tools. It has a different cmdline interface, and is just
a thin wrapper around the kexec_file_load syscall. It supports loading
the kernel and the ramdisk only for the exec-on-crash use case.
Bug: 237380224
Test: run kexec on Microdroid
Change-Id: I75610d4f55c97a79a7200ecf9e8aa7fc7b12c010
diff --git a/microdroid/kdump/Android.bp b/microdroid/kdump/Android.bp
new file mode 100644
index 0000000..1a8c9cc
--- /dev/null
+++ b/microdroid/kdump/Android.bp
@@ -0,0 +1,10 @@
+package {
+ default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+cc_binary {
+ name: "microdroid_kexec",
+ stem: "kexec",
+ srcs: ["kexec.c"],
+ installable: false,
+}
diff --git a/microdroid/kdump/kexec.c b/microdroid/kdump/kexec.c
new file mode 100644
index 0000000..65ea0ea
--- /dev/null
+++ b/microdroid/kdump/kexec.c
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// This program loads kernel and initrd which the system will boot into when
+// panic occurs.
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/kexec.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+static int open_checked(const char* path) {
+ int fd = open(path, O_RDONLY);
+ if (fd == -1) {
+ fprintf(stderr, "Failed to open %s: %s\n", path, strerror(errno));
+ exit(1);
+ }
+ return fd;
+}
+
+int main(int argc, const char* argv[]) {
+ if (argc != 4) {
+ fprintf(stderr, "Usage: %s <kernel> <initrd> <commandline>\n", argv[0]);
+ return 1;
+ }
+
+ // TODO(b/238272206): consider harding these
+ const char* kernel = argv[1];
+ const char* initrd = argv[2];
+ const char* cmdline = argv[3];
+ unsigned long cmdline_len = strlen(cmdline) + 1; // include null terminator, otherwise EINVAL
+
+ if (syscall(SYS_kexec_file_load, open_checked(kernel), open_checked(initrd), cmdline_len,
+ cmdline, KEXEC_FILE_ON_CRASH) == -1) {
+ fprintf(stderr, "Failed to load panic kernel: %s\n", strerror(errno));
+ return 1;
+ }
+ return 0;
+}