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SubjectRe: [PATCHv5 02/19] mm: Do not use zero page in encrypted pages
On 07/19/2018 12:16 AM, Kirill A. Shutemov wrote:
> 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.

I think we should make the zero page work. If folks are
security-sensitive, they need to write to guarantee it isn't being
shared. That's a pretty low bar.

I'm struggling to think of a case where an attacker has access to the
encrypted data, the virt->phys mapping, *and* can glean something
valuable from the presence of the zero page.

Please spend some time and focus on your patch descriptions. Use facts
that are backed up and are *precise* or tell the story of how your patch
was developed. In this case, citing the "security boundary" is not
precise enough without explaining what the boundary is and how it is

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