Bug 1563834 - Missing msr kernel module
Summary: Missing msr kernel module
Alias: None
Product: Fedora
Classification: Fedora
Component: msr-tools
Version: 27
Hardware: Unspecified
OS: Unspecified
Target Milestone: ---
Assignee: Greg Bailey
QA Contact: Fedora Extras Quality Assurance
Depends On:
TreeView+ depends on / blocked
Reported: 2018-04-04 20:32 UTC by Bryan Roessler
Modified: 2018-07-11 02:14 UTC (History)
1 user (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Last Closed: 2018-07-11 02:14:24 UTC
Type: Bug

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Description Bryan Roessler 2018-04-04 20:32:46 UTC
Description of problem:
msr-tools does not contain the corresponding msr kernel module so values cannot be written using wrmsr

Version-Release number of selected component (if applicable):

Steps to Reproduce:
1. install msr-tools
2. attempt to write (for example) an msr offset: sudo wrmsr 0x150 0x80000011ecc00000

Actual results: wrmsr: pwrite: Operation not permitted

Expected results: value written

Additional info: the msr kernel module necessary to write values is missing from the package/distro:

lsmod| grep msr (returns nothing)

Comment 1 Greg Bailey 2018-07-06 13:13:00 UTC
Kernels built for Fedora (and RHEL / CentOS) appear to have the msr module compiled directly into the kernel as opposed to being built as a separate module:

[root@localhost ~]# grep CONFIG_X86_MSR /boot/config-4.16.3-301.fc28.x86_64 

Because of the above, I'm not aware of any need for any separate module to be loaded, as the msr interface is already available:

[root@localhost ~]# ls -l /dev/cpu/0/msr 
crw-------. 1 root root 202, 0 Jul  6 12:40 /dev/cpu/0/msr

Comment 2 Bryan Roessler 2018-07-11 02:13:58 UTC
>sudo wrmsr 0x150 0x80000011F9A00000
wrmsr: pwrite: Operation not permitted

Based on googling, the error thrown was the same as when the msr module was missing. Based on your information I did some further research and found that by default the msr module does not play nicely with secure boot:


Looks like that was the issue all along.

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