Synopsis

Important: kernel security update

Type/Severity

Security Advisory: Important

Topic

An update for kernel is now available for Red Hat Enterprise Linux 5 Extended Lifecycle Support.

Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

[Updated 4th September 2019]
The Problem Description text has been updated to fix a list of architectures addressed by the CVE-2017-5753 mitigation. No changes have been made to the packages.

Description

The kernel packages contain the Linux kernel, the core of any Linux operating system.

Security Fix(es):

An industry-wide issue was found in the way many modern microprocessor designs have implemented speculative execution of instructions (a commonly used performance optimization). There are three primary variants of the issue which differ in the way the speculative execution can be exploited.

Note: This issue is present in hardware and cannot be fully fixed via software update. The updated kernel packages provide software mitigation for this hardware issue at a cost of potential performance penalty. Please refer to References section for further information about this issue and the performance impact.

In this update mitigations for IBM zSeries (S390), x86, and x86-64 architectures are provided.

• Variant CVE-2017-5753 triggers the speculative execution by performing a bounds-check bypass. It relies on the presence of a precisely-defined instruction sequence in the privileged code as well as the fact that memory accesses may cause allocation into the microprocessor's data cache even for speculatively executed instructions that never actually commit (retire). As a result, an unprivileged attacker could use this flaw to cross the syscall boundary and read privileged memory by conducting targeted cache side-channel attacks. (CVE-2017-5753, Important, S390, x86, and x86-64)
• Variant CVE-2017-5715 triggers the speculative execution by utilizing branch target injection. It relies on the presence of a precisely-defined instruction sequence in the privileged code as well as the fact that memory accesses may cause allocation into the microprocessor's data cache even for speculatively executed instructions that never actually commit (retire). As a result, an unprivileged attacker could use this flaw to cross the syscall and guest/host boundaries and read privileged memory by conducting targeted cache side-channel attacks. (CVE-2017-5715, Important, S390)
• Variant CVE-2017-5754 relies on the fact that, on impacted microprocessors, during speculative execution of instruction permission faults, exception generation triggered by a faulting access is suppressed until the retirement of the whole instruction block. In a combination with the fact that memory accesses may populate the cache even when the block is being dropped and never committed (executed), an unprivileged local attacker could use this flaw to read privileged (kernel space) memory by conducting targeted cache side-channel attacks. (CVE-2017-5754, Important, x86-64)

Red Hat would like to thank Google Project Zero for reporting these issues.

Solution

For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.

Affected Products

• Red Hat Enterprise Linux Server - Extended Life Cycle Support 5 x86_64
• Red Hat Enterprise Linux Server - Extended Life Cycle Support 5 i386
• Red Hat Enterprise Linux Server - Extended Life Cycle Support (for IBM z Systems) 5 s390x

Fixes

• BZ - 1519778 - CVE-2017-5753 hw: cpu: speculative execution bounds-check bypass
• BZ - 1519780 - CVE-2017-5715 hw: cpu: speculative execution branch target injection
• BZ - 1519781 - CVE-2017-5754 hw: cpu: speculative execution permission faults handling

CVEs

(none)

References