Re: binfmt_elf: use ELF_ET_DYN_BASE only for PIE breaks asan

[Kostya Serebryany <kcc@google.com>]

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+Jakub Jelinek, who helped us migrate asan's shadow from high addresses
to 0x7fff7000 for a significant ~5% performance and code size gain.
(a few years ago)

--kcc

On Mon, Aug 7, 2017 at 10:24 AM, Dmitry Vyukov <dvyukov@google.com> wrote:

> Hello,
>
> The recent "binfmt_elf: use ELF_ET_DYN_BASE only for PIE" patch:
> https://github.com/torvalds/linux/commit/eab09532d40090698b05a07c1c87f3
> 9fdbc5fab5
> breaks user-space AddressSanitizer. AddressSanitizer makes assumptions
> about address space layout for substantial performance gains. There
> are multiple people complaining about this already:
> https://github.com/google/sanitizers/issues/837
> https://twitter.com/kayseesee/status/894594085608013825
> https://bugzilla.kernel.org/show_bug.cgi?id=196537
> AddressSanitizer maps shadow memory at [0x00007fff7000-0x10007fff7fff]
> expecting that non-pie binaries will be below 2GB and pie
> binaries/modules will be at 0x55 or 0x7f. This is not the first time
> kernel address space shuffling breaks sanitizers. The last one was the
> move to 0x55.
>
> Is it possible to make this change less aggressive and keep the
> executable under 2GB?
>
> In future please be mindful of user-space sanitizers and talk to
> address-sanitizer@googlegroups.com before shuffling address space.
>
> Thanks
>

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