Re: [PATCHv5 03/19] mm/ksm: Do not merge pages with different KeyIDs

[Kirill A. Shutemov]

On Wed, Jul 18, 2018 at 10:38:27AM -0700, Dave Hansen wrote:
> On 07/17/2018 04:20 AM, Kirill A. Shutemov wrote:
> > Pages encrypted with different encryption keys are not allowed to be
> > merged by KSM. Otherwise it would cross security boundary.
> 
> Let's say I'm using plain AES (not AES-XTS).  I use the same key in two
> keyid slots.  I map a page with the first keyid and another with the
> other keyid.
> 
> Won't they have the same cipertext?  Why shouldn't we KSM them?

We compare plain text, not ciphertext. And for good reason.

Comparing ciphertext would only make KSM successful for AES-ECB that
doesn't dependent on physical address of the page.

MKTME only supports AES-XTS (no plans to support AES-ECB). It effectively
disables KSM if we go with comparing ciphertext.

-- 
 Kirill A. Shutemov