[PATCH v3 0/4] KVM: allow mapping non-refcounted pages

[David Stevens]

Is there any feedback on these patches? CVE-2021-22543 was fixed by
disallowing mapping of non-refcounted memory. These patches add proper
support for mapping that type of memory.

-David

On Wed, Aug 25, 2021 at 11:50 AM David Stevens <stevensd at chromium.org> wrote:
>
> From: David Stevens <stevensd at chromium.org>
>
> This patch series adds support for mapping non-refcount VM_IO and
> VM_PFNMAP memory into the guest.
>
> Currently, the gfn_to_pfn functions require being able to pin the target
> pfn, so they will fail if the pfn returned by follow_pte isn't a
> ref-counted page.  However, the KVM secondary MMUs do not require that
> the pfn be pinned, since they are integrated with the mmu notifier API.
> This series adds a new set of gfn_to_pfn_page functions which parallel
> the gfn_to_pfn functions but do not pin the pfn. The new functions
> return the page from gup if it was present, so callers can use it and
> call put_page when done.
>
> The gfn_to_pfn functions should be depreciated, since as they are unsafe
> due to relying on trying to obtain a struct page from a pfn returned by
> follow_pte. I added new functions instead of simply adding another
> optional parameter to the existing functions to make it easier to track
> down users of the deprecated functions.
>
> This series updates x86 and arm64 secondary MMUs to the new API.
>
> v2 -> v3:
>  - rebase on kvm next branch
> v1 -> v2:
>  - Introduce new gfn_to_pfn_page functions instead of modifying the
>    behavior of existing gfn_to_pfn functions, to make the change less
>    invasive.
>  - Drop changes to mmu_audit.c
>  - Include Nicholas Piggin's patch to avoid corrupting refcount in the
>    follow_pte case, and use it in depreciated gfn_to_pfn functions.
>  - Rebase on kvm/next
>
> David Stevens (4):
>   KVM: mmu: introduce new gfn_to_pfn_page functions
>   KVM: x86/mmu: use gfn_to_pfn_page
>   KVM: arm64/mmu: use gfn_to_pfn_page
>   KVM: mmu: remove over-aggressive warnings
>
>  arch/arm64/kvm/mmu.c            |  26 +++--
>  arch/x86/kvm/mmu/mmu.c          |  50 +++++----
>  arch/x86/kvm/mmu/mmu_internal.h |   3 +-
>  arch/x86/kvm/mmu/paging_tmpl.h  |  23 ++--
>  arch/x86/kvm/mmu/tdp_mmu.c      |   6 +-
>  arch/x86/kvm/mmu/tdp_mmu.h      |   4 +-
>  arch/x86/kvm/x86.c              |   6 +-
>  include/linux/kvm_host.h        |  17 +++
>  virt/kvm/kvm_main.c             | 188 +++++++++++++++++++++++---------
>  9 files changed, 220 insertions(+), 103 deletions(-)
>
> --
> 2.33.0.rc2.250.ged5fa647cd-goog
>