In order to be able to read and write from/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.
Changelog v1 -> v2:
- Patch all source code files with s/__asm__ __volatile__/asm volatile/g.
- Split the module in two (rdmsr/wrmsr).
- Include the wrmsr module in the forbidden modules efi list.
- Code indentation and cleanup.
- Copyright year update.
- Implicit casting mask removed.
- Use the same assembly code for x86 and x86_64.
- Add missing documentation.
- Patch submited with Signed-off-by.
Signed-off-by: Jesús Diéguez Fernández <jesu...@gmail.com>
---
docs/grub.texi | 45 ++++++++++++++--
grub-core/Makefile.core.def | 16 ++++++
grub-core/commands/efi/shim_lock.c | 2 +-
grub-core/commands/i386/rdmsr.c | 84 ++++++++++++++++++++++++++++++
grub-core/commands/i386/wrmsr.c | 75 ++++++++++++++++++++++++++
include/grub/i386/rdmsr.h | 32 ++++++++++++
include/grub/i386/wrmsr.h | 29 +++++++++++
7 files changed, 277 insertions(+), 6 deletions(-)
create mode 100644 grub-core/commands/i386/rdmsr.c
create mode 100644 grub-core/commands/i386/wrmsr.c
create mode 100644 include/grub/i386/rdmsr.h
create mode 100644 include/grub/i386/wrmsr.h
diff --git a/docs/grub.texi b/docs/grub.texi
index ecaba9d5c..1d792b636 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -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
@@ -3953,6 +3954,7 @@ 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
@@ -4785,6 +4787,20 @@ 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.
+@end deffn
+
+
@node read
@subsection read
@@ -5223,6 +5239,17 @@ 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.
+@end deffn
+
@node xen_hypervisor
@subsection xen_hypervisor
@@ -5716,11 +5743,11 @@ 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
@@ -5831,6 +5858,8 @@ 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
@@ -5850,6 +5879,8 @@ 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
@@ -5869,6 +5900,8 @@ 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
@@ -5888,6 +5921,8 @@ 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
diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 2346bd291..a966a8f28 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -2484,3 +2484,19 @@ module = {
common = loader/i386/xen_file64.c;
extra_dist = loader/i386/xen_fileXX.c;
};
+module = {
+ name = rdmsr;
+ common = commands/i386/rdmsr.c;
+ enable = x86;
+ enable = i386_xen_pvh;
+ enable = i386_xen;
+ enable = x86_64_xen;
+};
+module = {
+ name = wrmsr;
+ common = commands/i386/wrmsr.c;
+ enable = x86;
+ enable = i386_xen_pvh;
+ enable = i386_xen;
+ enable = x86_64_xen;
+};
diff --git a/grub-core/commands/efi/shim_lock.c
b/grub-core/commands/efi/shim_lock.c
index 83568cb2b..764098cfc 100644
--- a/grub-core/commands/efi/shim_lock.c
+++ b/grub-core/commands/efi/shim_lock.c
@@ -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,
diff --git a/grub-core/commands/i386/rdmsr.c b/grub-core/commands/i386/rdmsr.c
new file mode 100644
index 000000000..08e5aee0b
--- /dev/null
+++ b/grub-core/commands/i386/rdmsr.c
@@ -0,0 +1,84 @@
+/* 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/i386/rdmsr.h>
+#include <grub/i18n.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_uint64_t addr, value;
+ char *ptr;
+ char buf[sizeof("XXXXXXXX")];
+
+ 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", value);
+ grub_env_set (ctxt->state[0].arg, buf);
+ }
+ else
+ grub_printf ("0x%llx\n", 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);
+}
diff --git a/grub-core/commands/i386/wrmsr.c b/grub-core/commands/i386/wrmsr.c
new file mode 100644
index 000000000..351b93f93
--- /dev/null
+++ b/grub-core/commands/i386/wrmsr.c
@@ -0,0 +1,75 @@
+/* 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/i386/wrmsr.h>
+#include <grub/i18n.h>
+
+GRUB_MOD_LICENSE("GPLv3+");
+
+static grub_command_t cmd_write;
+
+static grub_err_t
+grub_cmd_msr_write (grub_command_t cmd, int argc, char **argv)
+{
+ grub_uint64_t addr, value;
+ char *ptr;
+
+ 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_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"));
+
+ 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);
+}
diff --git a/include/grub/i386/rdmsr.h b/include/grub/i386/rdmsr.h
new file mode 100644
index 000000000..e907f1052
--- /dev/null
+++ b/include/grub/i386/rdmsr.h
@@ -0,0 +1,32 @@
+/*
+ * 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_CPU_MSR_READ_HEADER
+#define GRUB_CPU_MSR_READ_HEADER 1
+#endif
+
+extern __inline grub_uint64_t grub_msr_read (grub_uint64_t msr_id)
+{
+ grub_uint32_t low_id = msr_id, low, high;
+
+ asm volatile ( "rdmsr" : "=a"(low), "=d"(high) : "c"(low_id) );
+
+ return ((grub_uint64_t)high << 32) | low;
+}
+
+
diff --git a/include/grub/i386/wrmsr.h b/include/grub/i386/wrmsr.h
new file mode 100644
index 000000000..2e535b8fe
--- /dev/null
+++ b/include/grub/i386/wrmsr.h
@@ -0,0 +1,29 @@
+/*
+ * 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_CPU_MSR_WRITE_HEADER
+#define GRUB_CPU_MSR_WRITE_HEADER 1
+#endif
+
+extern __inline void grub_msr_write(grub_uint64_t msr_id, grub_uint64_t
msr_value)
+{
+ grub_uint32_t low_id = msr_id, low = msr_value, high = msr_value >> 32;
+
+ asm volatile ( "wrmsr" : : "c"(low_id), "a"(low), "d"(high) );
+}
+
--
2.17.1
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