sysctl and platform-op locks open to abuse

[This CNA information record relates to multiple CVEs; the

text explains which aspects/vulnerabilities correspond to which CVE.]

To manage the system, sysctl and platform operations are used by the

control domain or a possible Xenstore domain. Some of these operations

may not be executed in parallel, so a system-wide lock each is used.

The way those locks are acquired is, however, not providing any fairness.

Furthermore, with XSM/Flask in use, the lock acquire will, for some

operations, occur ahead of any permission checking.

The sysctl issue is CVE-2026-62426.

The platform-op issue is CVE-2026-62427.