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msr: Add new MSR modules (rdmsr/wrmsr) 

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 Vincent Batts
parent 8d417db48d
commit a728cd4d1d
7 changed files with 324 additions and 7 deletions
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53
docs/grub.texi
View File

@ -3931,6 +3931,7 @@ you forget a command, you can run the command @command{help}
* play:: Play a tune
* probe:: Retrieve device info
* pxe_unload:: Unload the PXE environment
* rdmsr:: Read values from model-specific registers
* read:: Read user input
* reboot:: Reboot your computer
* regexp:: Test if regular expression matches string
@ -3954,6 +3955,7 @@ you forget a command, you can run the command @command{help}
* verify_detached:: Verify detached digital signature
* videoinfo:: List available video modes
@comment * xen_*:: Xen boot commands for AArch64
* wrmsr:: Write values to model-specific registers
* xen_hypervisor:: Load xen hypervisor binary (only on AArch64)
* xen_module:: Load xen modules for xen hypervisor (only on AArch64)
@end menu
@ -4786,6 +4788,24 @@ This command is only available on PC BIOS systems.
@end deffn
@node rdmsr
@subsection rdmsr
@deffn Command: rdmsr 0xADDR [-v VARNAME]
Read a model-specific register at address 0xADDR. If the parameter
@option{-v} is used and an environment variable @var{VARNAME} is
given, set that environment variable to the value that was read.
Please note that on SMP systems, reading from a MSR that has a
scope per hardware thread, implies that the value that is returned
only applies to the particular cpu/core/thread that runs 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.
@end deffn
@node read
@subsection read
@ -5292,6 +5312,21 @@ successfully. If validation fails, it is set to a non-zero value.
List available video modes. If resolution is given, show only matching modes.
@end deffn
@node wrmsr
@subsection wrmsr
@deffn Command: wrmsr 0xADDR 0xVALUE
Write a 0xVALUE to a model-specific register at address 0xADDR.
Please note that on SMP systems, writing to a MSR that has a scope
per hardware thread, implies that the value that is written
only applies to the particular cpu/core/thread that runs 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.
@end deffn
@node xen_hypervisor
@subsection xen_hypervisor
@ -5785,11 +5820,11 @@ boot and the shim. This functionality is provided by the shim_lock module. It
is recommend to build in this and other required modules into the @file{core.img}.
All modules not stored in the @file{core.img} and the ACPI tables for the
@command{acpi} command have to be signed, e.g. using PGP. Additionally, the
@command{iorw} and the @command{memrw} commands are prohibited if the UEFI
secure boot is enabled. This is done due to security reasons. All above
mentioned requirements are enforced by the shim_lock module. And itself it
is a persistent module which means that it cannot be unloaded if it was
loaded into the memory.
@command{iorw}, the @command{memrw} and the @command{wrmsr} commands are
prohibited if the UEFI secure boot is enabled. This is done due to
security reasons. All above mentioned requirements are enforced by the
shim_lock module. And itself it is a persistent module which means that
it cannot be unloaded if it was loaded into the memory.
@node Measured Boot
@section Measuring boot components
@ -5900,6 +5935,8 @@ to install to is specified, UUID is used instead as well.
@item USB @tab yes @tab yes @tab yes @tab yes
@item chainloader @tab local @tab yes @tab yes @tab no
@item cpuid @tab partial @tab partial @tab partial @tab partial
@item rdmsr @tab partial @tab partial @tab partial @tab partial
@item wrmsr @tab partial @tab partial @tab partial @tab partial
@item hints @tab guess @tab guess @tab guess @tab guess
@item PCI @tab yes @tab yes @tab yes @tab yes
@item badram @tab yes @tab yes @tab yes @tab yes
@ -5919,6 +5956,8 @@ to install to is specified, UUID is used instead as well.
@item USB @tab yes @tab yes @tab yes @tab no
@item chainloader @tab local @tab local @tab no @tab local
@item cpuid @tab partial @tab partial @tab partial @tab no
@item rdmsr @tab partial @tab partial @tab partial @tab no
@item wrmsr @tab partial @tab partial @tab partial @tab no
@item hints @tab guess @tab guess @tab good @tab guess
@item PCI @tab yes @tab yes @tab yes @tab no
@item badram @tab yes @tab yes @tab no @tab yes
@ -5938,6 +5977,8 @@ to install to is specified, UUID is used instead as well.
@item USB @tab yes @tab no @tab no @tab no
@item chainloader @tab yes @tab no @tab no @tab no
@item cpuid @tab no @tab no @tab no @tab no
@item rdmsr @tab no @tab no @tab no @tab no
@item wrmsr @tab no @tab no @tab no @tab no
@item hints @tab good @tab good @tab good @tab no
@item PCI @tab yes @tab no @tab no @tab no
@item badram @tab yes (*) @tab no @tab no @tab no
@ -5957,6 +5998,8 @@ to install to is specified, UUID is used instead as well.
@item USB @tab N/A @tab yes @tab no
@item chainloader @tab yes @tab no @tab yes
@item cpuid @tab no @tab no @tab yes
@item rdmsr @tab no @tab no @tab yes
@item wrmsr @tab no @tab no @tab yes
@item hints @tab guess @tab no @tab no
@item PCI @tab no @tab no @tab no
@item badram @tab yes (*) @tab no @tab no

11
grub-core/Makefile.core.def
View File

@ -2547,7 +2547,16 @@ module = {
common = loader/i386/xen_file64.c;
extra_dist = loader/i386/xen_fileXX.c;
};
module = {
name = rdmsr;
common = commands/i386/rdmsr.c;
enable = x86;
};
module = {
name = wrmsr;
common = commands/i386/wrmsr.c;
enable = x86;
};
module = {
name = fwconfig;
common = commands/fwconfig.c;

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
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@ -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);
}

36
include/grub/i386/rdmsr.h Normal file
View File

@ -0,0 +1,36 @@
/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2019 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/>.
*/
#ifndef GRUB_RDMSR_H
#define GRUB_RDMSR_H 1
/*
* TODO: Add a general protection exception handler.
* Accessing a reserved or unimplemented MSR address results in a GP#.
*/
extern inline grub_uint64_t grub_msr_read (grub_uint32_t msr_id)
{
grub_uint32_t low, high;
asm volatile ("rdmsr" : "=a" (low), "=d" (high) : "c" (msr_id));
return ((grub_uint64_t)high << 32) | low;
}
#endif /* GRUB_RDMSR_H */

34
include/grub/i386/wrmsr.h Normal file
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@ -0,0 +1,34 @@
/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2019 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/>.
*/
#ifndef GRUB_WRMSR_H
#define GRUB_WRMSR_H 1
/*
* TODO: Add a general protection exception handler.
* Accessing a reserved or unimplemented MSR address results in a GP#.
*/
extern inline void grub_msr_write(grub_uint32_t msr_id, grub_uint64_t msr_value)
{
grub_uint32_t low = msr_value, high = msr_value >> 32;
asm volatile ("wrmsr" : : "c" (msr_id), "a" (low), "d" (high));
}
#endif /* GRUB_WRMSR_H */