CoreCVE
Back

MEDIUM

Spectre v2 SMT mitigations problem in Linux kernel

Published Apr 21, 2023

Description

The Linux kernel allows userspace processes to enable mitigations by calling prctl with PR_SET_SPECULATION_CTRL which disables the speculation feature as well as by using seccomp. We had noticed that on VMs of at least one major cloud provider, the kernel still left the victim process exposed to attacks in some cases even after enabling the spectre-BTI mitigation with prctl. The same behavior can be observed on a bare-metal machine when forcing the mitigation to IBRS on boot command line.

This happened because when plain IBRS was enabled (not enhanced IBRS), the kernel had some logic that determined that STIBP was not needed. The IBRS bit implicitly protects against cross-thread branch target injection. However, with legacy IBRS, the IBRS bit was cleared on returning to userspace, due to performance reasons, which disabled the implicit STIBP and left userspace threads vulnerable to cross-thread branch target injection against which STIBP protects.

Affected products

Remediation

Red Hat mitigation

This flaw can be mitigated by disabling Simultaneous Multithreading (SMT). For instructions on how to disable SMT in RHEL, please see https://access.redhat.com/solutions/rhel-smt.

Metrics

Weaknesses (3)

CWE-1303

CWE-203

CWE-653

References (9)

Change history (0)

No recorded changes yet.

Sources
CVE.org / MITRE
Status PUBLISHED
Assigner Google
Published Apr 21, 2023
Updated Feb 13, 2025
Reserved Apr 12, 2023
Link CVE-2023-1998
CISA Vulnrichment
Updated Feb 4, 2025
NVD
Status Modified
Modified Jun 17, 2026
Link CVE-2023-1998
Red Hat
Severity Moderate
Public date Apr 12, 2023
Links CVE-2023-1998 - Bugzilla