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msr: Add new MSR modules (rdmsr/wrmsr)

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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>
This commit is contained in:
Jesús Diéguez Fernández 2019-03-08 01:26:37 +01:00 • committed by Daniel Kiper
parent 3611c4f42e
commit 46f5d51343
7 changed files with 324 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

2
grub-core/commands/efi/shim_lock.c
View file

@ -43,7 +43,7 @@ static grub_efi_guid_t shim_lock_guid = GRUB_EFI_SHIM_LOCK_GUID;
static grub_efi_shim_lock_protocol_t *sl;
/* List of modules which cannot be loaded if UEFI secure boot mode is enabled. */
static const char * const disabled_mods[] = {"iorw", "memrw", NULL};
static const char * const disabled_mods[] = {"iorw", "memrw", "wrmsr", NULL};
static grub_err_t
shim_lock_init (grub_file_t io, enum grub_file_type type,

102
grub-core/commands/i386/rdmsr.c Normal file
View file

@ -0,0 +1,102 @@
/* rdmsr.c - Read 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/rdmsr.h>
GRUB_MOD_LICENSE("GPLv3+");
static grub_extcmd_t cmd_read;
static const struct grub_arg_option options[] =
{
{0, 'v', 0, N_("Save read value into variable VARNAME."),
N_("VARNAME"), ARG_TYPE_STRING},
{0, 0, 0, 0, 0, 0}
};
static grub_err_t
grub_cmd_msr_read (grub_extcmd_context_t ctxt, int argc, char **argv)
{
grub_uint32_t manufacturer[3], max_cpuid, a, b, c, features, addr;
grub_uint64_t value;
char *ptr;
char buf[sizeof("1122334455667788")];
/*
* 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 != 1)
return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("one argument 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"));
value = grub_msr_read (addr);
if (ctxt->state[0].set)
{
grub_snprintf (buf, sizeof(buf), "%llx", (unsigned long long) value);
grub_env_set (ctxt->state[0].arg, buf);
}
else
grub_printf ("0x%llx\n", (unsigned long long) value);
return GRUB_ERR_NONE;
}
GRUB_MOD_INIT(rdmsr)
{
cmd_read = grub_register_extcmd ("rdmsr", grub_cmd_msr_read, 0, N_("ADDR"),
N_("Read a CPU model specific register."),
options);
}
GRUB_MOD_FINI(rdmsr)
{
grub_unregister_extcmd (cmd_read);
}

93
grub-core/commands/i386/wrmsr.c Normal file
View file

@ -0,0 +1,93 @@
/* 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);
}