CVE-2023-0045: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-0045 is a vulnerability discovered in the Linux kernel's implementation of the prctl syscall for Spectre-BTI mitigation. The vulnerability was discovered in January 2023 and affects Linux kernel versions prior to commit a664ec9158eeddd75121d39c9a0758016097fa96. The issue occurs because the ibprctlset function updates the Thread Information Flags (TIFs) for the task and updates the SPEC_CTRL MSR, but fails to issue an IBPB immediately during the syscall (CVE Details, Ubuntu Security).

The vulnerability exists in the kernel's implementation of speculative execution mitigations. When a user-space task requests Spectre v2 mitigation via prctl, the ibprctlset function updates the Thread Information Flags and SPEC_CTRL MSR but only issues the Indirect Branch Prediction Barrier (IBPB) on the next schedule when the TIF bits are checked. This leaves a window of vulnerability where the process is exposed to values already injected in the Branch Target Buffer (BTB) prior to the prctl syscall (GitHub Security).

The vulnerability could allow a local or remote attacker to leak sensitive information from applications that rely on Spectre v2 mitigation. The vulnerability has been assigned a CVSS score of 7.5 (High), indicating significant potential impact (NetApp Security).

The vulnerability was fixed in Linux kernel commit a664ec9158eeddd75121d39c9a0758016097fa96, which adds an immediate IBPB flush in ibprctlset(). For systems that cannot immediately update, a temporary workaround is to add a usleep call after the prctl call to force a reschedule and ensure correct mitigation (GitHub Security).