Missing/incomplete/"unknown" data about CPU vulnerabilities

[emanruse]

Qubes OS release

4.2.3

Brief summary

Some CPU vulnerabilities are reported with missing/incomplete info.

Steps to reproduce

grep . /sys/devices/system/cpu/vulnerabilities/*

or

lscpu

Expected behavior

Meaningful info about each vulnerability and mitigations.

Actual behavior

There is no actual info about some vulnerabilities. Examples of "unknown":

/sys/devices/system/cpu/vulnerabilities/srbds:Unknown: Dependent on hypervisor status

or

/sys/devices/system/cpu/vulnerabilities/mmio_stale_data:Mitigation: Clear CPU buffers; SMT Host state unknown

The later one is additionally confusing considering, considering the output of journalctl:

[    1.661691] dom0 kernel: cpu 1 spinlock event irq 141
[    1.662029] dom0 kernel: MMIO Stale Data CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/processor_mmio_stale_data.html for more details.
[    1.662046] dom0 kernel: cpu 2 spinlock event irq 142
[    1.662049] dom0 kernel: cpu 3 spinlock event irq 143

[HW42]

In VMs (including dom0) the kernel doesn't have full information about the system. So (as the first message you quoted already hints at) you need to look at the hypervisor. Take a look at xl dmesg (or /var/log/xen/console/hypervisor.log) and see what Xen thinks. In particular the messages starting with Speculative mitigation facilities.

If you think that for a specific vulnerability Linux running inside a Xen VM actually should be able to determine whether the system is susceptible to it, that would be a feature request (or maybe bug) for upstream.

[github-actions]

This issue has been closed as "not applicable." Here are some common examples of cases in which issues are closed as not applicable:

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