Re: powerpc/iommu: Avoid undefined right shift in iommu_range_alloc()

On Tue, 2017-08-08 at 07:06:32 UTC, Michael Ellerman wrote:

In iommu_range_alloc() we generate a mask by right shifting ~0,
however if the specified alignment is 0 then we right shift by 64,
which is undefined. UBSAN tells us so:

  UBSAN: Undefined behaviour in ../arch/powerpc/kernel/iommu.c:193:35
  shift exponent 64 is too large for 64-bit type 'long unsigned int'

We can avoid it by instead generating the mask with:

  align_mask = (1ull << align_order) - 1;

That will also generate an undefined shift if align_order is 64 or
greater, but that shouldn't be a problem for a while.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Applied to powerpc next.

https://git.kernel.org/powerpc/c/63b85621d9aa6bdc410f01b22f7821

cheers