privacyguides
/
privacytools.io
Archived
1
0
Fork 0
Code Issues 304 Pull Requests 47 Activity

operating-systems: expand the Linux instructions for MDS mitigation

This commit is contained in:
Mikaela Suomalainen 2019-08-28 13:48:27 +03:00
parent bf17094c87
commit e7c1dde9d3
No known key found for this signature in database
GPG Key ID: 0C207F07B2F32B67
1 changed files with 28 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
_includes/sections/operating-systems.html
View File

@ -39,7 +39,34 @@ tor="http://sejnfjrq6szgca7v.onion"
<ul>
<li><a href="#win10"><i class="fas fa-link"></i> Don't use Windows 10 - It's a privacy nightmare</a></li>
<li>Linux users check for CPU vulnerabilities, <code>tail -n +1 /sys/devices/system/cpu/vulnerabilities/*</code>. Vulnerable SMT can be disabled either in the UEFI BIOS or in kernel level by <code>sudo mkdir /etc/default/grub.d/ && echo GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT mds=full,nosmt" | sudo tee /etc/default/grub.d/mds.conf && sudo update-grub</code></li>
<li>Disable multithreading to mitigate <a href="https://mdsattacks.com/">RIDL and Fallout: MDS attacks on mdsattacks.com</a>. See also the next topic</li>
</ul>
<h4 id=linuxcpuvulns>Remember to check CPU vulnerability mitigations on Linux</h4>
<p><em>This also affects Windows 10, but it doesn't expose this information or mitigation instructions as easily.</em></p>
<p>When running a enough recent kernel, you can check the CPU vulnerabilities it detects by <code>tail -n +1 /sys/devices/system/cpu/vulnerabilities/*</code>. By using <code>tail -n +1</code> instead of <code>cat</code> the file names are also visible.</p>
<p>In case you have a Intel CPU, you will likely see that <a href="https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html">MDS - Microarchitectural Data Sampling</a> is only partially mitigated ("SMT vulnerable"), unless you have disabled it in UEFI BIOS as the full mitigation disables <a href="https://en.wikipedia.org/wiki/Simultaneous_multithreading">Simultaneous multithreading</a> which may be the cause of the highest performance impact.</p>
<p>The following steps can be took to enable the full mitigation assuming your system/distribution uses grub and supports <code>/etc/default/grub.d/</code>:</p>
<ol>
<li><code>sudo mkdir /etc/default/grub.d/</code> to create a directory for additional grub configuration
<li><code>echo GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT mds=full,nosmt" | sudo tee /etc/default/grub.d/mds.conf</code> to create a new grub config file source with the echoed content</li>
<li><code>sudo update-grub</code> to generate a new config file including these kernel flags
<li><code>sudo reboot</code> to reboot
<li>afterward the reboot check <code>tail -n +1 /sys/devices/system/cpu/vulnerabilities/*</code> again to see that MDS now says SMT disabled.
</ol>
<h5>Further reading</h5>
<ul>
<li><a href="https://cpu.fail/">CPU.fail</a></li>
<li><a href="https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html">MDS - Microarchitectural Data Sampling on The Linux kernel user's and administrator's guide</a></li>
<li><a href="https://mdsattacks.com/">RIDL and Fallout: MDS attacks on mdsattacks.com</a></li>
<li><a href="https://en.wikipedia.org/wiki/Simultaneous_multithreading">Simultaneous multithreading on Wikipedia</a></li>
</ul>
<h3>Worth Mentioning</h3>