RHSA-2018:0151: Important: kernel security and bug fix update

First published: Thu Jan 25 2018(Updated: )

The kernel packages contain the Linux kernel, the core of any Linux operating system.<br>Security Fix(es):<br>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.<br>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.<br>In this update initial mitigations for IBM Power (PowerPC) and IBM zSeries (S390) architectures are provided.<br><li> 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. This fix specifically addresses S390 processors. (CVE-2017-5715, Important)</li> <li> 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. This fix specifically addresses S390 and PowerPC processors. (CVE-2017-5753, Important)</li> <li> 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. Note: CVE-2017-5754 affects Intel x86-64 microprocessors. AMD x86-64 microprocessors are not affected by this issue. This fix specifically addresses PowerPC processors. (CVE-2017-5754, Important)</li> Red Hat would like to thank Google Project Zero for reporting CVE-2017-5715, CVE-2017-5753, and CVE-2017-5754.<br>This update also fixes the following security issues and bugs:<br>Space precludes documenting all of the bug fixes and enhancements included in this advisory. To see the complete list of bug fixes and enhancements, refer to the following KnowledgeBase article: <a href="https://access.redhat.com/articles/3327131." target="_blank">https://access.redhat.com/articles/3327131.</a>

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