On 2/18/2021 3:55 AM, David Hildenbrand wrote:
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@xxxxxxxxxx>
Change-Id: Iae6b1e4bb8216955ffc14af255a7eaaa6f35324d
Not sure this is the right thing to do, see
https://lkml.kernel.org/r/bcf8925d-0949-3fe1-baa8-cc536c529860@xxxxxxxxxx
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 :)
Since David's patch we're having trouble with the iBFT ACPI table, which
is mapped in via kmap() - see acpi_map() in "drivers/acpi/osl.c". KASAN
detects that it is being used after free when ibft_init() accesses the
iBFT table, but as of yet we can't find where it get's freed (we've
instrumented calls to kunmap()).
Thank you,
George
