> On Feb 16, 2023, at 09:35, Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote: > > Users can specify the hugetlb page size in the mmap, shmget and > memfd_create system calls. This is done by using 6 bits within the > flags argument to encode the base-2 logarithm of the desired page size. > The routine hstate_sizelog() uses the log2 value to find the > corresponding hugetlb hstate structure. Converting the log2 value > (page_size_log) to potential hugetlb page size is the simple statement: > > 1UL << page_size_log > > Because only 6 bits are used for page_size_log, the left shift can not > be greater than 63. This is fine on 64 bit architectures where a long > is 64 bits. However, if a value greater than 31 is passed on a 32 bit > architecture (where long is 32 bits) the shift will result in undefined > behavior. This was generally not an issue as the result of the > undefined shift had to exactly match hugetlb page size to proceed. > > Recent improvements in runtime checking have resulted in this undefined > behavior throwing errors such as reported below. > > Fix by comparing page_size_log to BITS_PER_LONG before doing shift. > > Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx> > Link: https://lore.kernel.org/lkml/CA+G9fYuei_Tr-vN9GS7SfFyU1y9hNysnf=PB7kT0=yv4MiPgVg@xxxxxxxxxxxxxx/ > Fixes: 42d7395feb56 ("mm: support more pagesizes for MAP_HUGETLB/SHM_HUGETLB") > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> Thanks.
