1.1 --- a/src/os_cpu/linux_x86/vm/os_linux_x86.cpp Mon Sep 23 08:56:19 2013 -0700
1.2 +++ b/src/os_cpu/linux_x86/vm/os_linux_x86.cpp Wed Sep 25 13:58:13 2013 +0200
1.3 @@ -876,3 +876,46 @@
1.4 #endif
1.5 }
1.6 #endif
1.7 +
1.8 +
1.9 +/*
1.10 + * IA32 only: execute code at a high address in case buggy NX emulation is present. I.e. avoid CS limit
1.11 + * updates (JDK-8023956).
1.12 + */
1.13 +void os::workaround_expand_exec_shield_cs_limit() {
1.14 +#if defined(IA32)
1.15 + size_t page_size = os::vm_page_size();
1.16 + /*
1.17 + * Take the highest VA the OS will give us and exec
1.18 + *
1.19 + * Although using -(pagesz) as mmap hint works on newer kernel as you would
1.20 + * think, older variants affected by this work-around don't (search forward only).
1.21 + *
1.22 + * On the affected distributions, we understand the memory layout to be:
1.23 + *
1.24 + * TASK_LIMIT= 3G, main stack base close to TASK_LIMT.
1.25 + *
1.26 + * A few pages south main stack will do it.
1.27 + *
1.28 + * If we are embedded in an app other than launcher (initial != main stack),
1.29 + * we don't have much control or understanding of the address space, just let it slide.
1.30 + */
1.31 + char* hint = (char*) (Linux::initial_thread_stack_bottom() -
1.32 + ((StackYellowPages + StackRedPages + 1) * page_size));
1.33 + char* codebuf = os::reserve_memory(page_size, hint);
1.34 + if ( (codebuf == NULL) || (!os::commit_memory(codebuf, page_size, true)) ) {
1.35 + return; // No matter, we tried, best effort.
1.36 + }
1.37 + if (PrintMiscellaneous && (Verbose || WizardMode)) {
1.38 + tty->print_cr("[CS limit NX emulation work-around, exec code at: %p]", codebuf);
1.39 + }
1.40 +
1.41 + // Some code to exec: the 'ret' instruction
1.42 + codebuf[0] = 0xC3;
1.43 +
1.44 + // Call the code in the codebuf
1.45 + __asm__ volatile("call *%0" : : "r"(codebuf));
1.46 +
1.47 + // keep the page mapped so CS limit isn't reduced.
1.48 +#endif
1.49 +}
