1 files changed, 94 insertions, 0 deletions
diff --git a/grub-core/commands/i386/wrmsr.c b/grub-core/commands/i386/wrmsr.c
new file mode 100644
index 0000000..1b143b8
--- /dev/null
+++ b/grub-core/commands/i386/wrmsr.c
@@ -0,0 +1,94 @@
+/* wrmsr.c - Write CPU model-specific registers. */
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2019  Free Software Foundation, Inc.
+ *  Based on gcc/gcc/config/i386/driver-i386.c
+ *
+ *  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/dl.h>
+#include <grub/misc.h>
+#include <grub/mm.h>
+#include <grub/env.h>
+#include <grub/command.h>
+#include <grub/extcmd.h>
+#include <grub/lockdown.h>
+#include <grub/i18n.h>
+#include <grub/i386/cpuid.h>
+#include <grub/i386/wrmsr.h>
+
+GRUB_MOD_LICENSE("GPLv3+");
+
+static grub_command_t cmd_write;
+
+static grub_err_t
+grub_cmd_msr_write (grub_command_t cmd __attribute__ ((unused)), int argc, char **argv)
+{
+  grub_uint32_t manufacturer[3], max_cpuid, a, b, c, features, addr;
+  grub_uint64_t value;
+  const char *ptr;
+
+  /*
+   * The CPUID instruction should be used to determine whether MSRs
+   * are supported. (CPUID.01H:EDX[5] = 1)
+   */
+  if (!grub_cpu_is_cpuid_supported ())
+    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
+
+  grub_cpuid (0, max_cpuid, manufacturer[0], manufacturer[2], manufacturer[1]);
+
+  if (max_cpuid < 1)
+    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
+
+  grub_cpuid (1, a, b, c, features);
+
+  if (!(features & (1 << 5)))
+    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
+
+  if (argc != 2)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("two arguments expected"));
+
+  grub_errno = GRUB_ERR_NONE;
+  ptr = argv[0];
+  addr = grub_strtoul (ptr, &ptr, 0);
+
+  if (grub_errno != GRUB_ERR_NONE)
+    return grub_errno;
+  if (*ptr != '\0')
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("invalid argument"));
+
+  ptr = argv[1];
+  value = grub_strtoull (ptr, &ptr, 0);
+
+  if (grub_errno != GRUB_ERR_NONE)
+    return grub_errno;
+  if (*ptr != '\0')
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("invalid argument"));
+
+  grub_msr_write (addr, value);
+
+  return GRUB_ERR_NONE;
+}
+
+GRUB_MOD_INIT(wrmsr)
+{
+  cmd_write = grub_register_command_lockdown ("wrmsr", grub_cmd_msr_write, N_("ADDR VALUE"),
+                                              N_("Write a value to a CPU model specific register."));
+}
+
+GRUB_MOD_FINI(wrmsr)
+{
+  grub_unregister_command (cmd_write);
+}