On Wed, 15 Feb 2023, Mike Kravetz 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>
Looks good to me. Reviewed-by: Jesper Juhl <jesperjuhl76@xxxxxxxxx>
