Spectre v2 SMT mitigations problem in Linux kernel
Summary
Spectre v2 SMT mitigations problem in Linux kernel
Original description
The description as published by the source.
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.
Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2023-1998 linux Fixed in: 5.10.178-1
- Ubuntu UBUNTU-CVE-2023-1998 linux-aws Fixed in: 4.4.0-1130.136
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov
- patch github.com
- web git.kernel.org
- web kernel.dance
- web lists.debian.org
- web lists.debian.org