I don’t think the article claims that a Java process tries to access some other process’s memory.
In a typical modern operating system, a memory page can be non-writable and non-executable, writable and non-executable, or non-writable and executable, but not simultaneously writable AND executable.
If you generate executable code at runtime, then you need write access to a page to write the executable code into that page. Then you need to tell the operating system to change the page from writable to executable.
If you then try to write to the page, you’ll get a signal (SIGSEGV or SIGBUS, according to the article).
Oracle’s JVM apparently relies on this behavior: a Java process sometimes tries to write to a page (in its own memory space) that is not marked writable. The JVM then catches the SIGSEGV and recovers (perhaps by asking the operating system to change the page back from executable to writable, or by arranging to write to a different page, or to abort the write operation altogether).
In a typical modern operating system, a memory page can be non-writable and non-executable, writable and non-executable, or non-writable and executable, but not simultaneously writable AND executable.
If you generate executable code at runtime, then you need write access to a page to write the executable code into that page. Then you need to tell the operating system to change the page from writable to executable.
If you then try to write to the page, you’ll get a signal (SIGSEGV or SIGBUS, according to the article).
Oracle’s JVM apparently relies on this behavior: a Java process sometimes tries to write to a page (in its own memory space) that is not marked writable. The JVM then catches the SIGSEGV and recovers (perhaps by asking the operating system to change the page back from executable to writable, or by arranging to write to a different page, or to abort the write operation altogether).