Making open source more inclusive
Red Hat is committed to replacing problematic language in our code, documentation, and web properties. We are beginning with these four terms: master, slave, blacklist, and whitelist. Because of the enormity of this endeavor, these changes will be implemented gradually over several upcoming releases. For more details, see our CTO Chris Wright’s message.
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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, 126.96.36.199) 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