a728cd4d1d
In order to be able to read from and write to model-specific registers, two new modules are added. They are i386 specific, as the cpuid module. rdmsr module registers the command rdmsr that allows reading from a MSR. wrmsr module registers the command wrmsr that allows writing to a MSR. wrmsr module is disabled if UEFI secure boot is enabled. Please note that on SMP systems, interacting with a MSR that has a scope per hardware thread, implies that the value only applies to the particular cpu/core/thread that ran the command. Also, if you specify a reserved or unimplemented MSR address, it will cause a general protection exception (which is not currently being handled) and the system will reboot. Signed-off-by: Jesús Diéguez Fernández <jesusdf@gmail.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
93 lines
2.6 KiB
C
93 lines
2.6 KiB
C
/* 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/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;
|
|
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 ("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);
|
|
}
|