Tests on the main 64-bit architectures prove that the ASLR is stable and doesAddress Space Layout Randomization (ASLR) is an exploit mitigation technique
not result in noticeable performance degradationimplemented 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
should make exploitation more difficult.
By default use address map randomization for PIE binaries and disTests on the tier 1 64-bit architectures proved that the ASLR is stable SBRK,and does
in order to allow to utilize the bss grow region for mappings.not result in noticeable performance degradation, therefore it should be safe to
Both settings are respected only in case the ASLR is enabledenable this mechanism by default. Moreover its effectiveness is increased for
the PIE (Position Independentent Executables) binaries - thanks to the
commit 9a227a2fd642 ("Enable PIE by default on 64-bit architectures"),
it is enough to control usage of ASLR in the OS solely by the sysctls.
AlthoughThis patch toggles the tests on 32-bit architectures with ASLR enabledkernel settings to use address map randomization for
were mostly passedPIE & non-PIE 64-bit binaries. It also disables SBRK, the issues may be encounteredin order to allow to utilize
for high memory consumption cases (e.gthe bss grow region for mappings. buildworld).The latter is respected only in case the
ThereforeASLR is enabled, so do it for all architectures.
As for the sakdrawbacks, a consequence of safety keepusing the ASLR is disabled for 32-bitmore significant
VM fragmentation, hence the issues may be encountered in the systems with
a limited address space in the high memory consumption cases, such as the 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. Also, for the sake of safety keep the feature disabled for 32-bit
executables on 64-bit machines, too.
The commited change may also slightly impact debuggers usage, therefore a care
should be taken when analyzing backtraces and using `disable-randomization`
flag in gdb.
In case any change in the OS behavior is observed, that can be possibly
caused by this patch, it is recommended to use firstname.lastname@example.org
mailing list for reporting and discussing the encountered issue. Also,
in order to confirm/rule-out the dependency on ASLR it is strongly advised
to re-run the test with the feature disabled - it can be done by settings
the following sysctls in the /etc/sysctl.conf file: