David Kaplan

**Name of the Vulnerable Software and Affected Versions** Xen (affected versions not specified) **Description** The issue relates to the context switch logic within Xen. Specifically, Xen attempts to skip an IBPB (Instruction Barrier Page Base) when a virtual CPU (vCPU) returns to a CPU it previously ran on. While this action maintains isolation between vCPUs from Xen's perspective, it prevents the guest kernel from correctly isolating between tasks. This can lead to a scenario where a new task is executed with the training data of a previous task still present in the Branch Target Buffer (BTB). **Recommendations** At the moment, there is no information about a newer version that contains a fix for this vulnerability.

**Name of the Vulnerable Software and Affected Versions** Linux kernel (affected versions not specified) **Description** The issue is related to a bug in the x86/kexec component of the Linux kernel, where the call to `cc platform has()` triggers a fault and system crash if call depth tracking is active. This occurs because the GS segment has been reset by `load segments()` and `GS BASE` is now 0, but call depth tracking uses per-CPU variables to operate. The fix involves calling `cc platform has()` earlier in the function when GS is still valid. **Recommendations** At the moment, there is no information about a newer version that contains a fix for this vulnerability.