While testing the success rate of Spectre-BTI attacks, It was observed that the kernel does not issue an IBPB immediately during the syscall. The ib_prctl_set function updates the Thread Information Flags (TIFs) for the task and updates the SPEC_CTRL MSR on the function __speculation_ctrl_update, but the IBPB is only issued on the next schedule, when the TIF bits are checked. This leaves the victim vulnerable to values already injected on the BTB, prior to the prctl syscall. The behavior is only corrected after a reschedule of the taks happens. Furthermore, the kernel entrance (due to the syscall itself), does not issue an IBPB in the default scenarios (i.e., when the kernel protects itself via retpoline or eIBRS). Refer: https://github.com/es0j/CVE-2023-0045/blob/main/README.md https://github.com/google/security-research/security/advisories/GHSA-9x5g-vmxf-4qj8