Dave Hansen wrote: > On 10/22/2013 06:52 AM, Kirill A. Shutemov wrote: > > Matthew noticed that hugetlb doesn't participate in ASLR on x86-64. > > The reason is genereic hugetlb_get_unmapped_area() which is used on > > x86-64. It doesn't support randomization and use bottom-up unmapped area > > lookup, instead of usual top-down on x86-64. > > I have to wonder if this was on purpose in order to keep the large and > small mappings separate. We don't *have* to keep them separate this, of > course, but it makes me wonder. I haven't seen any evidence that it's on purpose, but who knows... In x86-specific hugetlb_get_unmapped_area() there's explicit check what is mm->get_unmapped_area top-down or bottom-up, and doing the same. > > x86 has arch-specific hugetlb_get_unmapped_area(), but it's used only on > > x86-32. > > > > Let's use arch-specific hugetlb_get_unmapped_area() on x86-64 too. > > It fixes the issue and make hugetlb use top-down unmapped area lookup. > > Shouldn't we fix the generic code instead of further specializing the > x86 stuff? For that we need to modify info.low_limit to mm->mmap_legacy_base (which is x86 specific, no-go) or switch to top-down and set info.high_limit to mm->mmap_base. I don't know how it can affect other architectures. > In any case, you probably also want to run this through: the > libhugetlbfs tests: > > http://sourceforge.net/p/libhugetlbfs/code/ci/master/tree/tests/ I've got the same fail list for upstream and patched kernel, so no regression was found. ********** TEST SUMMARY * 2M * 32-bit 64-bit * Total testcases: 107 110 * Skipped: 0 0 * PASS: 98 108 * FAIL: 2 2 * Killed by signal: 7 0 * Bad configuration: 0 0 * Expected FAIL: 0 0 * Unexpected PASS: 0 0 * Strange test result: 0 0 ********** -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>