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