m/p/kexec: add minimal kexec library
This adds a minimal kexec library which wraps the kexec_file_load
syscall in a Go-style interface.
Change-Id: Ia69b47ec6a305b19b238f30a7515aabdccb44bb9
Reviewed-on: https://review.monogon.dev/c/monogon/+/903
Tested-by: Jenkins CI
Reviewed-by: Sergiusz Bazanski <serge@monogon.tech>
diff --git a/metropolis/pkg/kexec/BUILD.bazel b/metropolis/pkg/kexec/BUILD.bazel
new file mode 100644
index 0000000..61da706
--- /dev/null
+++ b/metropolis/pkg/kexec/BUILD.bazel
@@ -0,0 +1,20 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+ name = "kexec",
+ srcs = ["kexec.go"],
+ importpath = "source.monogon.dev/metropolis/pkg/kexec",
+ visibility = ["//visibility:public"],
+ deps = select({
+ "@io_bazel_rules_go//go/platform:amd64": [
+ "@org_golang_x_sys//unix",
+ ],
+ "@io_bazel_rules_go//go/platform:arm64": [
+ "@org_golang_x_sys//unix",
+ ],
+ "@io_bazel_rules_go//go/platform:riscv64": [
+ "@org_golang_x_sys//unix",
+ ],
+ "//conditions:default": [],
+ }),
+)
diff --git a/metropolis/pkg/kexec/kexec.go b/metropolis/pkg/kexec/kexec.go
new file mode 100644
index 0000000..dc330ec
--- /dev/null
+++ b/metropolis/pkg/kexec/kexec.go
@@ -0,0 +1,35 @@
+//go:build amd64 || arm64 || riscv64
+// +build amd64 arm64 riscv64
+
+// Package kexec allows executing subsequent kernels from Linux userspace.
+package kexec
+
+import (
+ "fmt"
+ "os"
+ "runtime"
+
+ "golang.org/x/sys/unix"
+)
+
+// FileLoad loads the given kernel as the new kernel with the given initramfs
+// and cmdline. The kernel can be started by calling
+// unix.Reboot(unix.LINUX_REBOOT_CMD_KEXEC). The underlying syscall is only
+// available on x86_64, arm64 and riscv.
+// Parts of this function are taken from u-root's kexec package.
+func FileLoad(kernel, initramfs *os.File, cmdline string) error {
+ var flags int
+ var initramfsfd int
+ if initramfs != nil {
+ initramfsfd = int(initramfs.Fd())
+ } else {
+ flags |= unix.KEXEC_FILE_NO_INITRAMFS
+ }
+
+ if err := unix.KexecFileLoad(int(kernel.Fd()), initramfsfd, cmdline, flags); err != nil {
+ return fmt.Errorf("SYS_kexec_file_load(%d, %d, %s, %x) = %v", kernel.Fd(), initramfsfd, cmdline, flags, err)
+ }
+ runtime.KeepAlive(kernel)
+ runtime.KeepAlive(initramfs)
+ return nil
+}