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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
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36
include/grub/i386/rdmsr.h Normal file
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/*
* 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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/*
* 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 */