Messages in this thread | | | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH] x86, mm: get ASLR work for hugetlb mappings | Date | Tue, 22 Oct 2013 20:52:19 +0300 (EEST) |
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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
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