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From: Andy Lutomirski <luto@kernel.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	 Andrew Morton <akpm@linux-foundation.org>,
	X86 ML <x86@kernel.org>,  Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	 Borislav Petkov <bp@alien8.de>,
	Peter Zijlstra <peterz@infradead.org>,
	David Howells <dhowells@redhat.com>,
	 Kees Cook <keescook@chromium.org>,
	Kai Huang <kai.huang@linux.intel.com>,
	 Jacob Pan <jacob.jun.pan@linux.intel.com>,
	 Alison Schofield <alison.schofield@intel.com>,
	Linux-MM <linux-mm@kvack.org>,  kvm list <kvm@vger.kernel.org>,
	keyrings@vger.kernel.org,  LKML <linux-kernel@vger.kernel.org>,
	Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: [PATCH, RFC 45/62] mm: Add the encrypt_mprotect() system call for MKTME
Date: Mon, 17 Jun 2019 12:12:20 -0700
Message-ID: <CALCETrWFXSndmPH0OH4DVVrAyPEeKUUfNwo_9CxO-3xy9awq0g@mail.gmail.com> (raw)
In-Reply-To: <5cbfa2da-ba2e-ed91-d0e8-add67753fc12@intel.com>

On Mon, Jun 17, 2019 at 11:37 AM Dave Hansen <dave.hansen@intel.com> wrote:
>
> Tom Lendacky, could you take a look down in the message to the talk of
> SEV?  I want to make sure I'm not misrepresenting what it does today.
> ...
>
>
> >> I actually don't care all that much which one we end up with.  It's not
> >> like the extra syscall in the second options means much.
> >
> > The benefit of the second one is that, if sys_encrypt is absent, it
> > just works.  In the first model, programs need a fallback because
> > they'll segfault of mprotect_encrypt() gets ENOSYS.
>
> Well, by the time they get here, they would have already had to allocate
> and set up the encryption key.  I don't think this would really be the
> "normal" malloc() path, for instance.
>
> >>  How do we
> >> eventually stack it on top of persistent memory filesystems or Device
> >> DAX?
> >
> > How do we stack anonymous memory on top of persistent memory or Device
> > DAX?  I'm confused.
>
> If our interface to MKTME is:
>
>         fd = open("/dev/mktme");
>         ptr = mmap(fd);
>
> Then it's hard to combine with an interface which is:
>
>         fd = open("/dev/dax123");
>         ptr = mmap(fd);
>
> Where if we have something like mprotect() (or madvise() or something
> else taking pointer), we can just do:
>
>         fd = open("/dev/anything987");
>         ptr = mmap(fd);
>         sys_encrypt(ptr);

I'm having a hard time imagining that ever working -- wouldn't it blow
up if someone did:

fd = open("/dev/anything987");
ptr1 = mmap(fd);
ptr2 = mmap(fd);
sys_encrypt(ptr1);

So I think it really has to be:
fd = open("/dev/anything987");
ioctl(fd, ENCRYPT_ME);
mmap(fd);

But I really expect that the encryption of a DAX device will actually
be a block device setting and won't look like this at all.  It'll be
more like dm-crypt except without device mapper.

>
> Now, we might not *do* it that way for dax, for instance, but I'm just
> saying that if we go the /dev/mktme route, we never get a choice.
>
> > I think that, in the long run, we're going to have to either expand
> > the core mm's concept of what "memory" is or just have a whole
> > parallel set of mechanisms for memory that doesn't work like memory.
> ...
> > I expect that some day normal memory will  be able to be repurposed as
> > SGX pages on the fly, and that will also look a lot more like SEV or
> > XPFO than like the this model of MKTME.
>
> I think you're drawing the line at pages where the kernel can manage
> contents vs. not manage contents.  I'm not sure that's the right
> distinction to make, though.  The thing that is important is whether the
> kernel can manage the lifetime and location of the data in the page.

The kernel can manage the location of EPC pages, for example, but only
under extreme constraints right now.  The draft SGX driver can and
does swap them out and swap them back in, potentially at a different
address.

>
> Basically: Can the kernel choose where the page comes from and get the
> page back when it wants?
>
> I really don't like the current state of things like with SEV or with
> KVM direct device assignment where the physical location is quite locked
> down and the kernel really can't manage the memory.  I'm trying really
> hard to make sure future hardware is more permissive about such things.
>  My hope is that these are a temporary blip and not the new normal.
>
> > So, if we upstream MKTME as anonymous memory with a magic config
> > syscall, I predict that, in a few years, it will be end up inheriting
> > all downsides of both approaches with few of the upsides.  Programs
> > like QEMU will need to learn to manipulate pages that can't be
> > accessed outside the VM without special VM buy-in, so the fact that
> > MKTME pages are fully functional and can be GUP-ed won't be very
> > useful.  And the VM will learn about all these things, but MKTME won't
> > really fit in.
>
> Kai Huang (who is on cc) has been doing the QEMU enabling and might want
> to weigh in.  I'd also love to hear from the AMD folks in case I'm not
> grokking some aspect of SEV.
>
> But, my understanding is that, even today, neither QEMU nor the kernel
> can see SEV-encrypted guest memory.  So QEMU should already understand
> how to not interact with guest memory.  I _assume_ it's also already
> doing this with anonymous memory, without needing /dev/sme or something.

Let's find out!

If it's using anonymous memory, it must be very strange, since it
would more or less have to be mmapped PROT_NONE.  The thing that makes
anonymous memory in particular seem so awkward to me is that it's
fundamentally identified by it's *address*, which means it makes no
sense if it's not mapped.

>
> > And, one of these days, someone will come up with a version of XPFO
> > that could actually be upstreamed, and it seems entirely plausible
> > that it will be totally incompatible with MKTME-as-anonymous-memory
> > and that users of MKTME will actually get *worse* security.
>
> I'm not following here.  XPFO just means that we don't keep the direct
> map around all the time for all memory.  If XPFO and
> MKTME-as-anonymous-memory were both in play, I think we'd just be
> creating/destroying the MKTME-enlightened direct map instead of a
> vanilla one.

What I'm saying is that I can imagine XPFO also wanting to be
something other than anonymous memory.  I don't think we'll ever want
regular MAP_ANONYMOUS to enable XPFO by default because the
performance will suck.  Doing this seems odd:

ptr = mmap(MAP_ANONYMOUS);
sys_xpfo_a_pointer(ptr);

So I could imagine:

ptr = mmap(MAP_ANONYMOUS | MAP_XPFO);

or

fd = open("/dev/xpfo"); (or fd = memfd_create(..., XPFO);
ptr = mmap(fd);

I'm thinking that XPFO is a *lot* simpler under the hood if we just
straight-up don't support GUP on it.  Maybe we should call this
"strong XPFO".  Similarly, the kinds of things that want MKTME may
also want the memory to be entirely absent from the direct map.  And
the things that use SEV (as I understand it) *can't* usefully use the
memory for normal IO via GUP or copy_to/from_user(), so these things
all have a decent amount in common.

Another down side of anonymous memory (in my head, anyway -- QEMU
people should chime in) is that it seems awkward to use it for IO
techniques in which the back-end isn't in the QEMU process.  If
there's an fd involved, you can pass it around, feed it to things like
vfio, etc.  If there's no fd, it's stuck in the creating process.

And another silly argument: if we had /dev/mktme, then we could
possibly get away with avoiding all the keyring stuff entirely.
Instead, you open /dev/mktme and you get your own key under the hook.
If you want two keys, you open /dev/mktme twice.  If you want some
other program to be able to see your memory, you pass it the fd.

I hope this email isn't too rambling :)

--Andy


  reply index

Thread overview: 153+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-08 14:43 [PATCH, RFC 00/62] Intel MKTME enabling Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 01/62] mm: Do no merge VMAs with different encryption KeyIDs Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 02/62] mm: Add helpers to setup zero page mappings Kirill A. Shutemov
2019-05-29  7:21   ` Mike Rapoport
2019-05-08 14:43 ` [PATCH, RFC 03/62] mm/ksm: Do not merge pages with different KeyIDs Kirill A. Shutemov
2019-05-10 18:07   ` Dave Hansen
2019-05-13 14:27     ` Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 04/62] mm/page_alloc: Unify alloc_hugepage_vma() Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 05/62] mm/page_alloc: Handle allocation for encrypted memory Kirill A. Shutemov
2019-05-29  7:21   ` Mike Rapoport
2019-05-29 12:47     ` Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 06/62] mm/khugepaged: Handle encrypted pages Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 07/62] x86/mm: Mask out KeyID bits from page table entry pfn Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 08/62] x86/mm: Introduce variables to store number, shift and mask of KeyIDs Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 09/62] x86/mm: Preserve KeyID on pte_modify() and pgprot_modify() Kirill A. Shutemov
2019-06-14  9:15   ` Peter Zijlstra
2019-06-14 13:03     ` Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 10/62] x86/mm: Detect MKTME early Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 11/62] x86/mm: Add a helper to retrieve KeyID for a page Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 12/62] x86/mm: Add a helper to retrieve KeyID for a VMA Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 13/62] x86/mm: Add hooks to allocate and free encrypted pages Kirill A. Shutemov
2019-06-14  9:34   ` Peter Zijlstra
2019-06-14 11:04     ` Peter Zijlstra
2019-06-14 13:28       ` Kirill A. Shutemov
2019-06-14 13:43         ` Peter Zijlstra
2019-06-14 22:41           ` Kirill A. Shutemov
2019-06-17  9:25             ` Peter Zijlstra
2019-06-14 13:14     ` Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 14/62] x86/mm: Map zero pages into encrypted mappings correctly Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 15/62] x86/mm: Rename CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 16/62] x86/mm: Allow to disable MKTME after enumeration Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 17/62] x86/mm: Calculate direct mapping size Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 18/62] x86/mm: Implement syncing per-KeyID direct mappings Kirill A. Shutemov
2019-06-14  9:51   ` Peter Zijlstra
2019-06-14 22:43     ` Kirill A. Shutemov
2019-06-17  9:27       ` Peter Zijlstra
2019-06-17 14:43         ` Kirill A. Shutemov
2019-06-17 14:51           ` Peter Zijlstra
2019-06-17 15:17             ` Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 19/62] x86/mm: Handle encrypted memory in page_to_virt() and __pa() Kirill A. Shutemov
2019-06-14 11:10   ` Peter Zijlstra
2019-05-08 14:43 ` [PATCH, RFC 20/62] mm/page_ext: Export lookup_page_ext() symbol Kirill A. Shutemov
2019-06-14 11:12   ` Peter Zijlstra
2019-06-14 22:44     ` Kirill A. Shutemov
2019-06-17  9:30       ` Peter Zijlstra
2019-06-17 11:01         ` Kai Huang
2019-06-17 11:13           ` Huang, Kai
2019-05-08 14:43 ` [PATCH, RFC 21/62] mm/rmap: Clear vma->anon_vma on unlink_anon_vmas() Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 22/62] x86/pconfig: Set a valid encryption algorithm for all MKTME commands Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 23/62] keys/mktme: Introduce a Kernel Key Service for MKTME Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 24/62] keys/mktme: Preparse the MKTME key payload Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 25/62] keys/mktme: Instantiate and destroy MKTME keys Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 26/62] keys/mktme: Move the MKTME payload into a cache aligned structure Kirill A. Shutemov
2019-06-14 11:35   ` Peter Zijlstra
2019-06-14 17:10     ` Alison Schofield
2019-05-08 14:43 ` [PATCH, RFC 27/62] keys/mktme: Strengthen the entropy of CPU generated MKTME keys Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 28/62] keys/mktme: Set up PCONFIG programming targets for " Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 29/62] keys/mktme: Program MKTME keys into the platform hardware Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 30/62] keys/mktme: Set up a percpu_ref_count for MKTME keys Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 31/62] keys/mktme: Require CAP_SYS_RESOURCE capability " Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 32/62] keys/mktme: Store MKTME payloads if cmdline parameter allows Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 33/62] acpi: Remove __init from acpi table parsing functions Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 34/62] acpi/hmat: Determine existence of an ACPI HMAT Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 35/62] keys/mktme: Require ACPI HMAT to register the MKTME Key Service Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 36/62] acpi/hmat: Evaluate topology presented in ACPI HMAT for MKTME Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 37/62] keys/mktme: Do not allow key creation in unsafe topologies Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 38/62] keys/mktme: Support CPU hotplug for MKTME key service Kirill A. Shutemov
2019-05-08 14:43 ` [PATCH, RFC 39/62] keys/mktme: Find new PCONFIG targets during memory hotplug Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 40/62] keys/mktme: Program new PCONFIG targets with MKTME keys Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 41/62] keys/mktme: Support memory hotplug for " Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 42/62] mm: Generalize the mprotect implementation to support extensions Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 43/62] syscall/x86: Wire up a system call for MKTME encryption keys Kirill A. Shutemov
2019-05-29  7:21   ` Mike Rapoport
2019-05-29 18:12     ` Alison Schofield
2019-05-08 14:44 ` [PATCH, RFC 44/62] x86/mm: Set KeyIDs in encrypted VMAs for MKTME Kirill A. Shutemov
2019-06-14 11:44   ` Peter Zijlstra
2019-06-14 17:33     ` Alison Schofield
2019-06-14 18:26       ` Dave Hansen
2019-06-14 18:46         ` Alison Schofield
2019-06-14 19:11           ` Dave Hansen
2019-06-17  9:10             ` Peter Zijlstra
2019-05-08 14:44 ` [PATCH, RFC 45/62] mm: Add the encrypt_mprotect() system call " Kirill A. Shutemov
2019-06-14 11:47   ` Peter Zijlstra
2019-06-14 17:35     ` Alison Schofield
2019-06-14 11:51   ` Peter Zijlstra
2019-06-15  0:32     ` Alison Schofield
2019-06-17  9:08       ` Peter Zijlstra
2019-06-17 15:07   ` Andy Lutomirski
2019-06-17 15:28     ` Dave Hansen
2019-06-17 15:46       ` Andy Lutomirski
2019-06-17 18:27         ` Dave Hansen
2019-06-17 19:12           ` Andy Lutomirski [this message]
2019-06-17 21:36             ` Dave Hansen
2019-06-18  0:48               ` Kai Huang
2019-06-18  1:50                 ` Andy Lutomirski
2019-06-18  2:11                   ` Kai Huang
2019-06-18  4:24                     ` Andy Lutomirski
2019-06-18 14:19                   ` Dave Hansen
2019-06-18  0:05             ` Kai Huang
2019-06-18  0:15               ` Andy Lutomirski
2019-06-18  1:35                 ` Kai Huang
2019-06-18  1:43                   ` Andy Lutomirski
2019-06-18  2:23                     ` Kai Huang
2019-06-18  9:12                       ` Peter Zijlstra
2019-06-18 14:09                         ` Dave Hansen
2019-06-18 16:15                           ` Kirill A. Shutemov
2019-06-18 16:22                             ` Dave Hansen
2019-06-18 16:36                               ` Andy Lutomirski
2019-06-18 16:48                                 ` Dave Hansen
2019-06-18 14:13                 ` Dave Hansen
2019-06-17 23:59           ` Kai Huang
2019-06-18  1:34             ` Lendacky, Thomas
2019-06-18  1:40               ` Andy Lutomirski
2019-06-18  2:02                 ` Lendacky, Thomas
2019-06-18  4:19                 ` Andy Lutomirski
2019-05-08 14:44 ` [PATCH, RFC 46/62] x86/mm: Keep reference counts on encrypted VMAs " Kirill A. Shutemov
2019-06-14 11:54   ` Peter Zijlstra
2019-06-14 18:39     ` Alison Schofield
2019-05-08 14:44 ` [PATCH, RFC 47/62] mm: Restrict MKTME memory encryption to anonymous VMAs Kirill A. Shutemov
2019-06-14 11:55   ` Peter Zijlstra
2019-06-15  0:07     ` Alison Schofield
2019-05-08 14:44 ` [PATCH, RFC 48/62] selftests/x86/mktme: Test the MKTME APIs Kirill A. Shutemov
2019-05-08 17:09   ` Alison Schofield
2019-05-08 14:44 ` [PATCH, RFC 49/62] mm, x86: export several MKTME variables Kirill A. Shutemov
2019-06-14 11:56   ` Peter Zijlstra
2019-06-17  3:14     ` Kai Huang
2019-06-17  7:46       ` Peter Zijlstra
2019-06-17  8:39         ` Kai Huang
2019-06-17 11:25           ` Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 50/62] kvm, x86, mmu: setup MKTME keyID to spte for given PFN Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 51/62] iommu/vt-d: Support MKTME in DMA remapping Kirill A. Shutemov
2019-06-14 12:04   ` Peter Zijlstra
2019-05-08 14:44 ` [PATCH, RFC 52/62] x86/mm: introduce common code for mem encryption Kirill A. Shutemov
2019-05-08 16:58   ` Christoph Hellwig
2019-05-08 20:52     ` Jacob Pan
2019-05-08 21:21       ` Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 53/62] x86/mm: Use common code for DMA memory encryption Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 54/62] x86/mm: Disable MKTME on incompatible platform configurations Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 55/62] x86/mm: Disable MKTME if not all system memory supports encryption Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 56/62] x86: Introduce CONFIG_X86_INTEL_MKTME Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 57/62] x86/mktme: Overview of Multi-Key Total Memory Encryption Kirill A. Shutemov
2019-05-29  7:21   ` Mike Rapoport
2019-05-29 18:13     ` Alison Schofield
2019-07-14 18:16   ` Randy Dunlap
2019-07-15  9:02     ` Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 58/62] x86/mktme: Document the MKTME provided security mitigations Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 59/62] x86/mktme: Document the MKTME kernel configuration requirements Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 60/62] x86/mktme: Document the MKTME Key Service API Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 61/62] x86/mktme: Document the MKTME API for anonymous memory encryption Kirill A. Shutemov
2019-05-08 14:44 ` [PATCH, RFC 62/62] x86/mktme: Demonstration program using the MKTME APIs Kirill A. Shutemov
2019-05-29  7:30 ` [PATCH, RFC 00/62] Intel MKTME enabling Mike Rapoport
2019-05-29 18:20   ` Alison Schofield
2019-06-14 12:15 ` Peter Zijlstra

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