Re: [PATCH 1/2] x86/mm/KASLR: Fix the wrong calculation of kalsr region initial size

Thomas Garnier
2018-09-04T17:57:57Z

Thanks Baoquan!

Reviewed-by: Thomas Garnier <thgarnie@google.com>

On Wed, Aug 29, 2018 at 4:49 AM Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> On Wed, Aug 29, 2018 at 10:17:53AM +0800, Baoquan He wrote:
> > In memory KASLR, __PHYSICAL_MASK_SHIFT is taken to calculate the
> > initial size of the direct mapping region. This is right in the
> > old code where __PHYSICAL_MASK_SHIFT was equal to MAX_PHYSMEM_BITS,
> > 46bit, and only 4-level mode was supported.
> >
> > Later, in commit:
> > b83ce5ee91471d ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52"),
> > __PHYSICAL_MASK_SHIFT was changed to be 52 always, no matter it's
> > 5-level or 4-level. This is wrong for 4-level paging. Then when
> > adapt phyiscal memory region size based on available memory, it
> > will overflow if the amount of system RAM and the padding is bigger
> > than 64TB.
> >
> > In fact, here MAX_PHYSMEM_BITS should be used instead. Fix it by
> > by replacing __PHYSICAL_MASK_SHIFT with MAX_PHYSMEM_BITS.
> >
> > Signed-off-by: Baoquan He <bhe@redhat.com>
>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>
> --
> Kirill A. Shutemov

--
Thomas