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SubjectRe: [PATCHv5 02/19] mm: Do not use zero page in encrypted pages
On Wed, Jul 18, 2018 at 10:36:24AM -0700, Dave Hansen wrote:
> On 07/17/2018 04:20 AM, Kirill A. Shutemov wrote:
> > Zero page is not encrypted and putting it into encrypted VMA produces
> > garbage.
> >
> > We can map zero page with KeyID-0 into an encrypted VMA, but this would
> > be violation security boundary between encryption domains.
>
> Why? How is it a violation?
>
> It only matters if they write secrets. They can't write secrets to the
> zero page.

I believe usage of zero page is wrong here. It would indirectly reveal
content of supposedly encrypted memory region.

I can see argument why it should be okay and I don't have very strong
opinion on this.

If folks see it's okay to use zero page in encrypted VMAs I can certainly
make it work.

> Is this only because you accidentally inherited ->vm_page_prot on the
> zero page PTE?

Yes, in previous patchset I mapped zero page with wrong KeyID. This is one
of possible fixes for this.

--
Kirill A. Shutemov

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