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To:        Marcin Wojtas <>
Cc:        Li-Wen Hsu <>, freebsd-current <>, Fabien Thomas <>, MARECHAL Boris <>, Rafal Jaworowski <>, Damien DEVILLE <>
In-Reply-To: <>

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> On 18 Nov 2021, at 11:43, Marcin Wojtas <> wrote:
> czw., 18 lis 2021 o 19:07 Li-Wen Hsu <> napisa=C5=82(a):
>>> On Wed, Nov 17, 2021 at 6:30 AM Marcin Wojtas <> wrote:
>>> As of b014e0f15bc7 the ASLR (Address Space Layout
>>> Randomization) feature becomes enabled for the all 64-bit
>>> binaries by default.
>>> Address Space Layout Randomization (ASLR) is an exploit mitigation
>>> technique implemented in the majority of modern operating systems.
>>> It involves randomly positioning the base address of an executable
>>> and the position of libraries, heap, and stack, in a process's address
>>> space. Although over the years ASLR proved to not guarantee full OS
>>> security on its own, this mechanism can make exploitation more difficult=

>>> (especially when combined with other methods, such as W^X).
>>> Tests on the tier 1 64-bit architectures demonstrated that the ASLR is
>>> stable and does not result in noticeable performance degradation,
>>> therefore it is considered safe to enable this mechanism by default.
>>> Moreover its effectiveness is increased for PIE (Position Independent
>>> Executable) binaries. Thanks to commit 9a227a2fd642 ("Enable PIE by
>>> default on 64-bit architectures"), building from src is not necessary
>>> to have PIE binaries and it is enough to control usage of ASLR in the
>>> OS solely by setting the appropriate sysctls. The defaults were toggled
>>> for the 64-bit PIE and non-PIE executables.
>>> As for the drawbacks, a consequence of using the ASLR is more
>>> significant VM fragmentation, hence the issues may be encountered
>>> in the systems with a limited address space in high memory consumption
>>> cases, such as buildworld. As a result, although the tests on 32-bit
>>> architectures with ASLR enabled were mostly on par with what was
>>> observed on 64-bit ones, the defaults for the former are not changed
>>> at this time. Also, for the sake of safety the feature remains disabled
>>> for 32-bit executables on 64-bit machines, too.
>>> The committed change affects the overall OS operation, so the
>>> following should be taken into consideration:
>>> * Address space fragmentation.
>>> * A changed ABI due to modified layout of address space.
>>> * More complicated debugging due to:
>>>  * Non-reproducible address space layout between runs.
>>>  * Some debuggers automatically disable ASLR for spawned processes,
>>>    making target's environment different between debug and
>>>    non-debug runs.
>>> The known issues (such as PR239873 or PR253208) have been fixed in
>>> HEAD up front, however please pay attention to the system behavior after=

>>> upgrading the kernel to the newest revisions.
>>> In order to confirm/rule-out the dependency of any encountered issue
>>> on ASLR it is strongly advised to re-run the test with the feature
>>> disabled - it can be done by setting the following sysctls
>>> in the /etc/sysctl.conf file:
>>> kern.elf64.aslr.enable=3D0
>>> kern.elf64.aslr.pie_enable=3D0
>>> The change is a result of combined efforts under the auspices
>>> of the FreeBSD Foundation and the Semihalf team sponsored
>>> by Stormshield.
>>> Best regards,
>>> Marcin
>> Thanks very much for working on this. FYI, there are some test cases
>> seem to be affected by this:
>> The mkimg ones are a bit tricky, it seems the output is changed in
>> each run. We may need a way to generate reproducible results..
>> I'm still checking them, but hope more people can join and fix them.
> Thanks for bringing this up! Apart from
> sys.netpfil.common.dummynet.pf_nat other are 23 are new.

I=E2=80=99ve just managed to reproduce that one locally (it only happens if i=
pfw is also loaded) and will dig in soon. It=E2=80=99s not going to be aslr r=
elated. You can ignore that failure.=20


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