Messages in this thread | | | Subject | Re: [PATCH] mm, kasan: don't poison boot memory | From | David Hildenbrand <> | Date | Thu, 18 Feb 2021 09:55:07 +0100 |
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On 17.02.21 21:56, Andrey Konovalov wrote: > During boot, all non-reserved memblock memory is exposed to the buddy > allocator. Poisoning all that memory with KASAN lengthens boot time, > especially on systems with large amount of RAM. This patch makes > page_alloc to not call kasan_free_pages() on all new memory. > > __free_pages_core() is used when exposing fresh memory during system > boot and when onlining memory during hotplug. This patch adds a new > FPI_SKIP_KASAN_POISON flag and passes it to __free_pages_ok() through > free_pages_prepare() from __free_pages_core(). > > This has little impact on KASAN memory tracking. > > Assuming that there are no references to newly exposed pages before they > are ever allocated, there won't be any intended (but buggy) accesses to > that memory that KASAN would normally detect. > > However, with this patch, KASAN stops detecting wild and large > out-of-bounds accesses that happen to land on a fresh memory page that > was never allocated. This is taken as an acceptable trade-off. > > All memory allocated normally when the boot is over keeps getting > poisoned as usual. > > Signed-off-by: Andrey Konovalov <andreyknvl@google.com> > Change-Id: Iae6b1e4bb8216955ffc14af255a7eaaa6f35324d
Not sure this is the right thing to do, see
https://lkml.kernel.org/r/bcf8925d-0949-3fe1-baa8-cc536c529860@oracle.com
Reversing the order in which memory gets allocated + used during boot (in a patch by me) might have revealed an invalid memory access during boot.
I suspect that that issue would no longer get detected with your patch, as the invalid memory access would simply not get detected. Now, I cannot prove that :)
-- Thanks,
David / dhildenb
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