Re: [PATCHv3 0/5] x86: Enumerate TME and PCONFIG, add MKTME_KEY_PROG helper

[Ingo Molnar <mingo@kernel.org>]

* Kirill A. Shutemov <kirill@shutemov.name> wrote:

> On Sun, Feb 11, 2018 at 08:02:41PM +0100, Ingo Molnar wrote:
> > 
> > * Kirill A. Shutemov <kirill.shutemov@linux.intel.com> wrote:
> > 
> > > Multikey Total Memory Encryption (MKTME)[1] is a technology that allows
> > > transparent memory encryption in upcoming Intel platforms.
> > >
> > > MKTME is built on top of TME. TME allows encryption of the entirety of
> > > system memory using a single key. MKTME allows to have multiple encryption
> > > domains, each having own key -- different memory pages can be encrypted
> > > with different keys.
> > > 
> > > The patchset does some ground work for MKTME enabling:
> > >   - Adds two new cpufeatures: TME and PCONFIG;
> > >   - Detects if BIOS enabled TME and MKTME;
> > >   - Enumerates what PCONFIG targets are supported;
> > >   - Provides helper to program encryption keys into CPU;
> > > 
> > > As part of TME enumeration we check out how many bits from physical address
> > > are claimed for encryption key ID. This may be critical as we or guest VM
> > > must not use these bits for physical address.
> > 
> > So how will the 'full' patchset look like, roughly - is there a tree or diffstat 
> > we could take a look at perhaps?
> 
> I don't have anything to show beyond this yet. I'll post as soon I have it
> ready.
> 
> This patchset includes only things that are close to hardware and unlikely
> to change substantially by the next steps.

Ok.

> > I'm also wondering how 'TME' compares to AMD's SME (Secure Memory Encryption) and 
> > SEV features. SME required a number of low level boot code changes - I'm wondering 
> > how much commonality there can be achieved with Intel's TME so that we don't end 
> > up with two sets of interfaces.
> 
> Unlike AMD SME, Intel TME doesn't really requires enabling on kernel side.
> 
> It's job of BIOS to get it enabled and by time kernel has control all
> memory it has access too is encrypted with the single TME key. BIOS
> exclude some of its memory for encryption to work properly.
> 
> What requires enabling is MKTME. As with TME, it gets enabled by BIOS: it
> reserves a number of upper bits from physical address to indicate KeyID.
> 
> This means we don't need to change anything during early boot. MKTME is
> targeted to userspace memory: typically to protect one VM from another.
> 
> Of course we can choose to use MKTME for kernel hardening and it may
> require changes during early boot, that's not part of my initial enabling
> plan.
> 
> Key design points of Intel MKTME:
> 
>  - Initial HW implementation would support upto 63 keys (plus one default
>    TME key). But the number of keys may be as low as 3, depending to SKU
>    and BIOS settings
> 
>  - To access encrypted memory you need to use mapping with proper KeyID
>    int the page table entry. KeyID is encoded in upper bits of PFN in page
>    table entry.
> 
>    This means we cannot use direct map to access encrypted memory from
>    kernel side. My idea is to re-use kmap() interface to get proper
>    temporary mapping on kernel side.
> 
>  - CPU does not enforce coherency between mappings of the same physical
>    page with different KeyIDs or encryption keys. We wound need to take
>    care about flushing cache on allocation of encrypted page and on
>    returning it back to free pool.
>
>  - For managing keys, there's MKTME_KEY_PROGRAM leaf of the new PCONFIG
>    (platform configuration) instruction. It allows load and clear keys
>    associated with a KeyID. You can also ask CPU to generate a key for
>    you or disable memory encryption when a KeyID is used.
> 
> If you have any questions I would be glad to answer.

Ok, this sounds pretty flexible at first glance - thanks for the summary!

	Ingo