[PATCH] Make EFI watchdog behaviour configurable

[Arthur Mesh <amesh@juniper.net>]

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Starting with d9a0c9413e81d3c0affc6383693bdd28dc863a5c, GRUB unconditionally
disables watchdog on EFI platforms. This opens up a window (starting at GRUB's
grub_efi_init(), until OS re-enables it) when EFI system operates w/o watchdog.
If an EFI system gets stuck in that window, the chipset will never reset the
system.

Add `--enable-efi-watchdog' configure argument, which defaults to Off.
When enabled, efi watchdog will not be disabled.
Otherwise, efi watchdog will be disabled.

Create a command line interface to enable/disable watchdog:
 efi-watchdog (enable|disable) <timeout>
---
 configure.ac              |   18 +++++++++++++-
 docs/grub.texi            |    8 ++++++
 grub-core/kern/efi/init.c |   59 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index c864311..91de439 100644
--- a/configure.ac
+++ b/configure.ac
@@ -211,7 +211,10 @@ esac
 case "$platform" in
   coreboot)	machine_CPPFLAGS="$machine_CPPFLAGS -DGRUB_MACHINE_COREBOOT=1" ;;
   multiboot)	machine_CPPFLAGS="$machine_CPPFLAGS -DGRUB_MACHINE_MULTIBOOT=1" ;;
-  efi)		machine_CPPFLAGS="$machine_CPPFLAGS -DGRUB_MACHINE_EFI=1" ;;
+  efi)		machine_CPPFLAGS="$machine_CPPFLAGS -DGRUB_MACHINE_EFI=1"
+	if test x"$enable_efi_watchdog" = xyes ; then
+		machine_CPPFLAGS="$machine_CPPFLAGS -DEFI_WATCHDOG_LEAVE_ALONE=1"
+	fi ;;
   xen)		machine_CPPFLAGS="$machine_CPPFLAGS -DGRUB_MACHINE_XEN=1" ;;
   ieee1275)	machine_CPPFLAGS="$machine_CPPFLAGS -DGRUB_MACHINE_IEEE1275=1" ;;
   uboot)	machine_CPPFLAGS="$machine_CPPFLAGS -DGRUB_MACHINE_UBOOT=1" ;;
@@ -1705,6 +1708,10 @@ if test x"$enable_werror" != xno ; then
   HOST_CFLAGS="$HOST_CFLAGS -Werror"
 fi
 
+AC_ARG_ENABLE([efi-watchdog],
+	      [AS_HELP_STRING([--enable-efi-watchdog],
+                             [Do not explicitly disable EFI watchdog])])
+
 TARGET_CPP="$TARGET_CC -E"
 TARGET_CCAS=$TARGET_CC
 
@@ -1899,6 +1906,15 @@ echo efiemu runtime: Yes
 else
 echo efiemu runtime: No "($efiemu_excuse)"
 fi
+
+if [ x"$platform" = xefi ]; then
+if [ x"$enable_efi_watchdog" != xyes ]; then
+echo disable EFI watchdog: Yes
+else
+echo disable EFI watchdog: No
+fi
+fi
+
 if [ x"$grub_mkfont_excuse" = x ]; then
 echo grub-mkfont: Yes
 else
diff --git a/docs/grub.texi b/docs/grub.texi
index b9f41a7..4cfd50c 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -3784,6 +3784,7 @@ you forget a command, you can run the command @command{help}
 * distrust::                    Remove a pubkey from trusted keys
 * drivemap::                    Map a drive to another
 * echo::                        Display a line of text
+* efi-watchdog::                Manipulate EFI watchdog
 * eval::                        Evaluate agruments as GRUB commands
 * export::                      Export an environment variable
 * false::                       Do nothing, unsuccessfully
@@ -4192,6 +4193,13 @@ When interpreting backslash escapes, backslash followed by any other
 character will print that character.
 @end deffn
 
+@node efi-watchdog
+@subsection efi-watchdog
+
+@deffn Command efi-watchdog enable|disable <timeout>
+Enable or disable the system's watchdog timer. Only available in EFI targeted
+GRUB.
+@end deffn
 
 @node eval
 @subsection eval
diff --git a/grub-core/kern/efi/init.c b/grub-core/kern/efi/init.c
index e9c85de..47053d2 100644
--- a/grub-core/kern/efi/init.c
+++ b/grub-core/kern/efi/init.c
@@ -25,9 +25,62 @@
 #include <grub/env.h>
 #include <grub/mm.h>
 #include <grub/kernel.h>
+#include <grub/extcmd.h>
+#include <grub/command.h>
 
 grub_addr_t grub_modbase;
 
+static grub_command_t cmd_list;
+
+static grub_err_t
+grub_cmd_efi_watchdog (grub_command_t cmd  __attribute__ ((unused)),
+		       int argc, char **args)
+{
+    long input;
+    grub_efi_status_t status;
+    grub_efi_uintn_t timeout;
+
+    if (argc < 1)
+	return grub_error (GRUB_ERR_BAD_ARGUMENT,
+	    N_("efi-watchdog (enable|disable) <timeout>"));
+
+    if (grub_strcasecmp (args[0], "enable") == 0) {
+
+	if (argc != 2)
+	    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+			       N_("efi-watchdog enable <timeout>"));
+
+	input = grub_strtol (args[1], 0, 0);
+
+	if (input >= 0) {
+	    timeout = input;
+	} else {
+	    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+			       N_("<timeout> must be non-negative"));
+	}
+
+    } else if (grub_strcasecmp (args[0], "disable") == 0) {
+
+	if (argc != 1)
+	    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+			       N_("efi-watchdog disable"));
+	timeout = 0;
+
+    } else {
+	return grub_error (GRUB_ERR_BAD_ARGUMENT,
+	    N_("efi-watchdog (enable|disable) <timeout>"));
+    }
+
+    status = efi_call_4 (grub_efi_system_table->boot_services->set_watchdog_timer,
+			 timeout, 0, sizeof(L"GRUB"), L"GRUB");
+
+    if (status != GRUB_EFI_SUCCESS)
+	return grub_error (GRUB_ERR_BUG,
+			   N_("EFI SetWatchdogTimer() bug"));
+    else
+	return GRUB_ERR_NONE;
+}
+
 void
 grub_efi_init (void)
 {
@@ -39,10 +92,15 @@ grub_efi_init (void)
   /* Initialize the memory management system.  */
   grub_efi_mm_init ();
 
+#ifndef EFI_WATCHDOG_LEAVE_ALONE
   efi_call_4 (grub_efi_system_table->boot_services->set_watchdog_timer,
 	      0, 0, 0, NULL);
+#endif
 
   grub_efidisk_init ();
+
+  cmd_list = grub_register_command ("efi-watchdog", grub_cmd_efi_watchdog, 0,
+				    N_("Enable/Disable system's watchdog timer."));
 }
 
 void (*grub_efi_net_config) (grub_efi_handle_t hnd, 
@@ -77,4 +135,5 @@ grub_efi_fini (void)
 {
   grub_efidisk_fini ();
   grub_console_fini ();
+  grub_unregister_command (cmd_list);
 }
-- 
1.7.9.5

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