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a8e911d135
If the kernel is configured with KASAN_EXTRA, the stack size is
increasted significantly because this option sets "-fstack-reuse" to
"none" in GCC [1]. As a result, it triggers stack overrun quite often
with 32k stack size compiled using GCC 8. For example, this reproducer
https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/madvise/madvise06.c
triggers a "corrupted stack end detected inside scheduler" very reliably
with CONFIG_SCHED_STACK_END_CHECK enabled.
There are just too many functions that could have a large stack with
KASAN_EXTRA due to large local variables that have been called over and
over again without being able to reuse the stacks. Some noticiable ones
are
size
7648 shrink_page_list
3584 xfs_rmap_convert
3312 migrate_page_move_mapping
3312 dev_ethtool
3200 migrate_misplaced_transhuge_page
3168 copy_process
There are other 49 functions are over 2k in size while compiling kernel
with "-Wframe-larger-than=" even with a related minimal config on this
machine. Hence, it is too much work to change Makefiles for each object
to compile without "-fsanitize-address-use-after-scope" individually.
[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715#c23
Although there is a patch in GCC 9 to help the situation, GCC 9 probably
won't be released in a few months and then it probably take another
6-month to 1-year for all major distros to include it as a default.
Hence, the stack usage with KASAN_EXTRA can be revisited again in 2020
when GCC 9 is everywhere. Until then, this patch will help users avoid
stack overrun.
This has already been fixed for arm64 for the same reason via
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