Linux Kernel RSB Underflow Mitigation Vulnerability

A vulnerability in the Linux kernel related to RSB (Return Stack Buffer) underflow and poisoning attacks has been addressed. This issue was particularly relevant for x86 architecture, where the kernel now fills the RSB on vmexit for IBRS (Indirect Branch Restricted Speculation) to prevent such underflow attacks. The vulnerability arose from the need to document and mitigate tribal knowledge about RSB attacks and their implications.

Impact

Exploitation of this vulnerability could lead to RSB underflow, allowing for poisoning attacks that could disrupt the normal execution flow of a program or the operating system.