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comparison src/os_cpu/linux_x86/vm/os_linux_x86.cpp @ 12313:899ecf76b570

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8023956: Provide a work-around to broken Linux 32 bit "Exec Shield" using CS for NX emulation (crashing with SI_KERNEL) Summary: Execute some code at a high virtual address value, and keep mapped Reviewed-by: coleenp, zgu
author dsimms
date Wed, 25 Sep 2013 13:58:13 +0200
parents af21010d1062
children cefad50507d8 de6a9e811145
comparison
equal deleted inserted replaced
12292:084b21cd0228 12313:899ecf76b570
874 #ifdef AMD64 874 #ifdef AMD64
875 assert(((intptr_t)os::current_stack_pointer() & (StackAlignmentInBytes-1)) == 0, "incorrect stack alignment"); 875 assert(((intptr_t)os::current_stack_pointer() & (StackAlignmentInBytes-1)) == 0, "incorrect stack alignment");
876 #endif 876 #endif
877 } 877 }
878 #endif 878 #endif
879
880
881 /*
882 * IA32 only: execute code at a high address in case buggy NX emulation is present. I.e. avoid CS limit
883 * updates (JDK-8023956).
884 */
885 void os::workaround_expand_exec_shield_cs_limit() {
886 #if defined(IA32)
887 size_t page_size = os::vm_page_size();
888 /*
889 * Take the highest VA the OS will give us and exec
890 *
891 * Although using -(pagesz) as mmap hint works on newer kernel as you would
892 * think, older variants affected by this work-around don't (search forward only).
893 *
894 * On the affected distributions, we understand the memory layout to be:
895 *
896 * TASK_LIMIT= 3G, main stack base close to TASK_LIMT.
897 *
898 * A few pages south main stack will do it.
899 *
900 * If we are embedded in an app other than launcher (initial != main stack),
901 * we don't have much control or understanding of the address space, just let it slide.
902 */
903 char* hint = (char*) (Linux::initial_thread_stack_bottom() -
904 ((StackYellowPages + StackRedPages + 1) * page_size));
905 char* codebuf = os::reserve_memory(page_size, hint);
906 if ( (codebuf == NULL) || (!os::commit_memory(codebuf, page_size, true)) ) {
907 return; // No matter, we tried, best effort.
908 }
909 if (PrintMiscellaneous && (Verbose || WizardMode)) {
910 tty->print_cr("[CS limit NX emulation work-around, exec code at: %p]", codebuf);
911 }
912
913 // Some code to exec: the 'ret' instruction
914 codebuf[0] = 0xC3;
915
916 // Call the code in the codebuf
917 __asm__ volatile("call *%0" : : "r"(codebuf));
918
919 // keep the page mapped so CS limit isn't reduced.
920 #endif
921 }