Using alt-java

OpenJDK 8

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OpenJDK 8 is a Red Hat offering on the Red Hat Enterprise Linux platform. The Using alt-java guide provides an overview of alt-java, defines the differences between java and alt-java, and explains how to use alt-java.

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Chapter 1. Overview of alt-java

The family of Spectre/Meltdown vulnerabilities includes Speculative Store Bypass (SSB), which may affect the Java VM (CVE-2018-3639).

Red Hat packages contain a mitigation for this vulnerability in the form of a patch for the Java binary. However, this patch reduces performance by up to 10% in some cases. This is described in RH1566890.

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 CPU release (1.8.0 282.b08, onwards the alt-java binary is included in OpenJDK 1.8.0 and 11 GA rpms.

Chapter 2. Differences between java and alt-java

“alt-java” is the same as “java”, except for the SSB mitigation. Refer, RH1750419.

Although the SBB mitigation patch is there only for x86-64 (Intel and AMD), the alt-java is present on all architectures. So on non-x86, the alt-java is identical to java without any patches.

Chapter 3. Using alt-java and java

3.1. Using alt-java

Use “alt-java” for any applications that run untrusted code. However, be aware that it is not a solution to all speculative execution vulnerabilities. For more information refer, Java and Speculative Execution Vulnerabilities.

3.2. Using java

Use the “java” binary for performance-critical tasks in a secure environment. All of the RPMs in a Red Hat Enterprise Linux system except IcedTea-Web use the “java” binary. IcedTea-Web may be used to run untrusted code, so it uses ”alt-java” as its launcher.

Chapter 4. Performance impact of alt-java

By moving the SSB mitigation to “alt-java”, the performance impact on “java” is removed.

Using “alt-java” may significantly reduce the performance of Java programs. You can find detailed information in Red Hat Bugzilla:

Revised on 2021-04-22 14:38:38 UTC

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