Linux Kernel KVM VMX RSB Underflow Vulnerability Prevention

A vulnerability in the Linux kernel's KVM VMX implementation has been addressed, which relates to the Return Stack Buffer (RSB) management during virtual machine transitions. The issue arose because balanced return calls could theoretically be interrupted by a Non-Maskable Interrupt (NMI), potentially causing an RSB underflow before the virtual machine entry (vmenter) process. To mitigate this risk, the vulnerability prevents any return actions, whether balanced or not, between the SPEC_CTRL write and the vmenter, ensuring a more secure transition process.

Impact

Exploitation of this vulnerability could lead to an RSB underflow, which may allow for manipulation of the return stack, potentially disrupting the execution flow of the virtual machine.