Chapter 1. Overview of alt-java

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Red Hat packages contain a mitigation for the SSB vulnerability in the form of a patch for the java binary. This patch disables an optimization present in x86-64 (Intel and AMD) processors. Disabling that optimization reduces the risk of kernel side-channel attacks, but also reduces CPU performance.

Since the patch reduces performance, it has been removed from the java launcher. A new binary alt-java is now available. From the January 2021 Critical Patch Update release (1.8.0 282.b08, 11.0.10.9) onwards, the alt-java binary is included in Red Hat build of OpenJDK 21 and Red Hat build of OpenJDK 11 GA RPM packages.

Additional resources

For more information about the performance impact of SSB mitigation, see Kernel Side-Channel Attack using Speculative Store Bypass - CVE-2018-3639 on the Red Hat Customer Portal
For more information about the java binary patch, see RH1566890 in the Red Hat Bugzilla documentation.

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