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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Raymund Will <rw@suse.com>
Date: Mon, 24 Oct 2022 14:33:50 -0400
Subject: [PATCH] loader: Add support for grub-emu to kexec Linux menu entries
The GRUB emulator is used as a debugging utility but it could also be
used as a user-space bootloader if there is support to boot an operating
system.
The Linux kernel is already able to (re)boot another kernel via the
kexec boot mechanism. So the grub-emu tool could rely on this feature
and have linux and initrd commands that are used to pass a kernel,
initramfs image and command line parameters to kexec for booting
a selected menu entry.
By default the systemctl kexec option is used so systemd can shutdown
all of the running services before doing a reboot using kexec. But if
this is not present, it can fall back to executing the kexec user-space
tool directly. The ability to force a kexec-reboot when systemctl kexec
fails must only be used in controlled environments to avoid possible
filesystem corruption and data loss.
Signed-off-by: Raymund Will <rw@suse.com>
Signed-off-by: John Jolly <jjolly@suse.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Robbie Harwood <rharwood@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
(cherry picked from commit e364307f6acc2f631b4c1fefda0791b9ce1f205f)
[rharwood: conflicts around makefile and grub_exit return code]
---
grub-core/Makefile.core.def | 3 -
grub-core/kern/emu/main.c | 4 +
grub-core/kern/emu/misc.c | 18 ++++-
grub-core/loader/emu/linux.c | 178 +++++++++++++++++++++++++++++++++++++++++++
include/grub/emu/exec.h | 4 +-
include/grub/emu/hostfile.h | 3 +-
include/grub/emu/misc.h | 3 +
docs/grub.texi | 30 ++++++--
grub-core/Makefile.am | 1 +
9 files changed, 230 insertions(+), 14 deletions(-)
create mode 100644 grub-core/loader/emu/linux.c
diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 741a033978..f21da23213 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -1864,11 +1864,8 @@ module = {
riscv32 = loader/riscv/linux.c;
riscv64 = loader/riscv/linux.c;
emu = loader/emu/linux.c;
-
common = loader/linux.c;
common = lib/cmdline.c;
- enable = noemu;
-
efi = loader/efi/linux.c;
};
diff --git a/grub-core/kern/emu/main.c b/grub-core/kern/emu/main.c
index 12277c34d2..68e2b283bb 100644
--- a/grub-core/kern/emu/main.c
+++ b/grub-core/kern/emu/main.c
@@ -107,6 +107,7 @@ static struct argp_option options[] = {
N_("use GRUB files in the directory DIR [default=%s]"), 0},
{"verbose", 'v', 0, 0, N_("print verbose messages."), 0},
{"hold", 'H', N_("SECS"), OPTION_ARG_OPTIONAL, N_("wait until a debugger will attach"), 0},
+ {"kexec", 'X', 0, 0, N_("use kexec to boot Linux kernels via systemctl (pass twice to enable dangerous fallback to non-systemctl)."), 0},
{ 0, 0, 0, 0, 0, 0 }
};
@@ -164,6 +165,9 @@ argp_parser (int key, char *arg, struct argp_state *state)
case 'v':
verbosity++;
break;
+ case 'X':
+ grub_util_set_kexecute ();
+ break;
case ARGP_KEY_ARG:
{
diff --git a/grub-core/kern/emu/misc.c b/grub-core/kern/emu/misc.c
index d278c2921f..02d27c3440 100644
--- a/grub-core/kern/emu/misc.c
+++ b/grub-core/kern/emu/misc.c
@@ -39,6 +39,7 @@
#include <grub/emu/misc.h>
int verbosity;
+int kexecute;
void
grub_util_warn (const char *fmt, ...)
@@ -82,7 +83,7 @@ grub_util_error (const char *fmt, ...)
vfprintf (stderr, fmt, ap);
va_end (ap);
fprintf (stderr, ".\n");
- exit (1);
+ grub_exit (1);
}
void *
@@ -154,6 +155,9 @@ void
__attribute__ ((noreturn))
grub_exit (int rc)
{
+#if defined (GRUB_KERNEL)
+ grub_reboot ();
+#endif
exit (rc < 0 ? 1 : rc);
}
#endif
@@ -215,3 +219,15 @@ grub_util_load_image (const char *path, char *buf)
fclose (fp);
}
+
+void
+grub_util_set_kexecute (void)
+{
+ kexecute++;
+}
+
+int
+grub_util_get_kexecute (void)
+{
+ return kexecute;
+}
diff --git a/grub-core/loader/emu/linux.c b/grub-core/loader/emu/linux.c
new file mode 100644
index 0000000000..0cf378a376
--- /dev/null
+++ b/grub-core/loader/emu/linux.c
@@ -0,0 +1,178 @@
+/*
+ * GRUB -- GRand Unified Bootloader
+ * Copyright (C) 2022 Free Software Foundation, Inc.
+ *
+ * GRUB is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * GRUB is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GRUB. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/loader.h>
+#include <grub/dl.h>
+#include <grub/command.h>
+#include <grub/time.h>
+
+#include <grub/emu/exec.h>
+#include <grub/emu/hostfile.h>
+#include <grub/emu/misc.h>
+
+GRUB_MOD_LICENSE ("GPLv3+");
+
+static grub_dl_t my_mod;
+
+static char *kernel_path;
+static char *initrd_path;
+static char *boot_cmdline;
+
+static grub_err_t
+grub_linux_boot (void)
+{
+ grub_err_t rc = GRUB_ERR_NONE;
+ char *initrd_param;
+ const char *kexec[] = {"kexec", "-la", kernel_path, boot_cmdline, NULL, NULL};
+ const char *systemctl[] = {"systemctl", "kexec", NULL};
+ int kexecute = grub_util_get_kexecute ();
+
+ if (initrd_path)
+ {
+ initrd_param = grub_xasprintf ("--initrd=%s", initrd_path);
+ kexec[3] = initrd_param;
+ kexec[4] = boot_cmdline;
+ }
+ else
+ initrd_param = grub_xasprintf ("%s", "");
+
+ grub_dprintf ("linux", "%serforming 'kexec -la %s %s %s'\n",
+ (kexecute) ? "P" : "Not p",
+ kernel_path, initrd_param, boot_cmdline);
+
+ if (kexecute)
+ rc = grub_util_exec (kexec);
+
+ grub_free (initrd_param);
+
+ if (rc != GRUB_ERR_NONE)
+ {
+ grub_error (rc, N_("error trying to perform kexec load operation"));
+ grub_sleep (3);
+ return rc;
+ }
+
+ if (kexecute < 1)
+ grub_fatal (N_("use '"PACKAGE"-emu --kexec' to force a system restart"));
+
+ grub_dprintf ("linux", "Performing 'systemctl kexec' (%s) ",
+ (kexecute==1) ? "do-or-die" : "just-in-case");
+ rc = grub_util_exec (systemctl);
+
+ if (kexecute == 1)
+ grub_fatal (N_("error trying to perform 'systemctl kexec': %d"), rc);
+
+ /*
+ * WARNING: forcible reset should only be used in read-only environments.
+ * grub-emu cannot check for these - users beware.
+ */
+ grub_dprintf ("linux", "Performing 'kexec -ex'");
+ kexec[1] = "-ex";
+ kexec[2] = NULL;
+ rc = grub_util_exec (kexec);
+ if (rc != GRUB_ERR_NONE)
+ grub_fatal (N_("error trying to directly perform 'kexec -ex': %d"), rc);
+
+ return rc;
+}
+
+static grub_err_t
+grub_linux_unload (void)
+{
+ /* Unloading: we're no longer in use. */
+ grub_dl_unref (my_mod);
+ grub_free (boot_cmdline);
+ boot_cmdline = NULL;
+ return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)), int argc,
+ char *argv[])
+{
+ int i;
+ char *tempstr;
+
+ /* Mark ourselves as in-use. */
+ grub_dl_ref (my_mod);
+
+ if (argc == 0)
+ return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("filename expected"));
+
+ if (!grub_util_is_regular (argv[0]))
+ return grub_error (GRUB_ERR_FILE_NOT_FOUND,
+ N_("cannot find kernel file %s"), argv[0]);
+
+ grub_free (kernel_path);
+ kernel_path = grub_xasprintf ("%s", argv[0]);
+
+ grub_free (boot_cmdline);
+ boot_cmdline = NULL;
+
+ if (argc > 1)
+ {
+ boot_cmdline = grub_xasprintf ("--command-line=%s", argv[1]);
+ for (i = 2; i < argc; i++)
+ {
+ tempstr = grub_xasprintf ("%s %s", boot_cmdline, argv[i]);
+ grub_free (boot_cmdline);
+ boot_cmdline = tempstr;
+ }
+ }
+
+ grub_loader_set (grub_linux_boot, grub_linux_unload, 0);
+
+ return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_cmd_initrd (grub_command_t cmd __attribute__ ((unused)), int argc,
+ char *argv[])
+{
+ if (argc == 0)
+ return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("filename expected"));
+
+ if (!grub_util_is_regular (argv[0]))
+ return grub_error (GRUB_ERR_FILE_NOT_FOUND,
+ N_("Cannot find initrd file %s"), argv[0]);
+
+ grub_free (initrd_path);
+ initrd_path = grub_xasprintf ("%s", argv[0]);
+
+ /* We are done - mark ourselves as on longer in use. */
+ grub_dl_unref (my_mod);
+
+ return GRUB_ERR_NONE;
+}
+
+static grub_command_t cmd_linux, cmd_initrd;
+
+GRUB_MOD_INIT (linux)
+{
+ cmd_linux = grub_register_command ("linux", grub_cmd_linux, 0,
+ N_("Load Linux."));
+ cmd_initrd = grub_register_command ("initrd", grub_cmd_initrd, 0,
+ N_("Load initrd."));
+ my_mod = mod;
+}
+
+GRUB_MOD_FINI (linux)
+{
+ grub_unregister_command (cmd_linux);
+ grub_unregister_command (cmd_initrd);
+}
diff --git a/include/grub/emu/exec.h b/include/grub/emu/exec.h
index d1073ef86a..1b61b4a2e5 100644
--- a/include/grub/emu/exec.h
+++ b/include/grub/emu/exec.h
@@ -23,6 +23,8 @@
#include <stdarg.h>
#include <sys/types.h>
+#include <grub/symbol.h>
+
pid_t
grub_util_exec_pipe (const char *const *argv, int *fd);
pid_t
@@ -32,7 +34,7 @@ int
grub_util_exec_redirect_all (const char *const *argv, const char *stdin_file,
const char *stdout_file, const char *stderr_file);
int
-grub_util_exec (const char *const *argv);
+EXPORT_FUNC(grub_util_exec) (const char *const *argv);
int
grub_util_exec_redirect (const char *const *argv, const char *stdin_file,
const char *stdout_file);
diff --git a/include/grub/emu/hostfile.h b/include/grub/emu/hostfile.h
index cfb1e2b566..a61568e36e 100644
--- a/include/grub/emu/hostfile.h
+++ b/include/grub/emu/hostfile.h
@@ -22,6 +22,7 @@
#include <grub/disk.h>
#include <grub/partition.h>
#include <sys/types.h>
+#include <grub/symbol.h>
#include <grub/osdep/hostfile.h>
int
@@ -29,7 +30,7 @@ grub_util_is_directory (const char *path);
int
grub_util_is_special_file (const char *path);
int
-grub_util_is_regular (const char *path);
+EXPORT_FUNC(grub_util_is_regular) (const char *path);
char *
grub_util_path_concat (size_t n, ...);
diff --git a/include/grub/emu/misc.h b/include/grub/emu/misc.h
index ff9c48a649..01056954b9 100644
--- a/include/grub/emu/misc.h
+++ b/include/grub/emu/misc.h
@@ -57,6 +57,9 @@ void EXPORT_FUNC(grub_util_warn) (const char *fmt, ...) __attribute__ ((format (
void EXPORT_FUNC(grub_util_info) (const char *fmt, ...) __attribute__ ((format (GNU_PRINTF, 1, 2)));
void EXPORT_FUNC(grub_util_error) (const char *fmt, ...) __attribute__ ((format (GNU_PRINTF, 1, 2), noreturn));
+void EXPORT_FUNC(grub_util_set_kexecute) (void);
+int EXPORT_FUNC(grub_util_get_kexecute) (void) WARN_UNUSED_RESULT;
+
grub_uint64_t EXPORT_FUNC (grub_util_get_cpu_time_ms) (void);
#ifdef HAVE_DEVICE_MAPPER
diff --git a/docs/grub.texi b/docs/grub.texi
index a4da9c2a1b..1750b72ee9 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -923,17 +923,17 @@ magic.
@node General boot methods
@section How to boot operating systems
-GRUB has two distinct boot methods. One of the two is to load an
-operating system directly, and the other is to chain-load another boot
-loader which then will load an operating system actually. Generally
-speaking, the former is more desirable, because you don't need to
-install or maintain other boot loaders and GRUB is flexible enough to
-load an operating system from an arbitrary disk/partition. However,
-the latter is sometimes required, since GRUB doesn't support all the
-existing operating systems natively.
+GRUB has three distinct boot methods: loading an operating system
+directly, using kexec from userspace, and chainloading another
+bootloader. Generally speaking, the first two are more desirable
+because you don't need to install or maintain other boot loaders and
+GRUB is flexible enough to load an operating system from an arbitrary
+disk/partition. However, chainloading is sometimes required, as GRUB
+doesn't support all existing operating systems natively.
@menu
* Loading an operating system directly::
+* Kexec::
* Chain-loading::
@end menu
@@ -959,6 +959,20 @@ use more complicated instructions. @xref{DOS/Windows}, for more
information.
+@node Kexec
+@subsection Kexec with grub2-emu
+
+GRUB can be run in userspace by invoking the grub2-emu tool. It will
+read all configuration scripts as if booting directly (see @xref{Loading
+an operating system directly}). With the @code{--kexec} flag, and
+kexec(8) support from the operating system, the @command{linux} command
+will directly boot the target image. For systems that lack working
+systemctl(1) support for kexec, passing the @code{--kexec} flag twice
+will fallback to invoking kexec(8) directly; note however that this
+fallback may be unsafe outside read-only environments, as it does not
+invoke shutdown machinery.
+
+
@node Chain-loading
@subsection Chain-loading an OS
diff --git a/grub-core/Makefile.am b/grub-core/Makefile.am
index c2e8a82bce..dd49939aaa 100644
--- a/grub-core/Makefile.am
+++ b/grub-core/Makefile.am
@@ -309,6 +309,7 @@ KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/emu/net.h
KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/emu/hostdisk.h
KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/emu/hostfile.h
KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/extcmd.h
+KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/emu/exec.h
if COND_GRUB_EMU_SDL
KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/sdl.h
endif
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