linux-kernel - Re: [RFC v2 PATCH 01/13] mm/shmem: Introduce F_SEAL

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 23 Nov 2021 10:06:02 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Hildenbrand <david@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        qemu-devel@...gnu.org, Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, john.ji@...el.com, susie.li@...el.com,
        jun.nakajima@...el.com, dave.hansen@...el.com, ak@...ux.intel.com
Subject: Re: [RFC v2 PATCH 01/13] mm/shmem: Introduce F_SEAL_GUEST

On 11/19/21 16:39, David Hildenbrand wrote:
>> If qmeu can put all the guest memory in a memfd and not map it, then
>> I'd also like to see that the IOMMU can use this interface too so we
>> can have VFIO working in this configuration.
> 
> In QEMU we usually want to (and must) be able to access guest memory
> from user space, with the current design we wouldn't even be able to
> temporarily mmap it -- which makes sense for encrypted memory only. The
> corner case really is encrypted memory. So I don't think we'll see a
> broad use of this feature outside of encrypted VMs in QEMU. I might be
> wrong, most probably I am:)

It's not _that_ crazy an idea, but it's going to be some work to teach 
KVM that it has to kmap/kunmap around all memory accesses.

I think it's great that memfd hooks are usable by more than one 
subsystem, OTOH it's fair that whoever needs it does the work---and VFIO 
does not need it for confidential VMs, yet, so it should be fine for now 
to have a single user.

On the other hand, as I commented already, the lack of locking in the 
register/unregister functions has to be fixed even with a single user. 
Another thing we can do already is change the guest_ops/guest_mem_ops to 
something like memfd_falloc_notifier_ops/memfd_pfn_ops, and the 
register/unregister functions to memfd_register/unregister_falloc_notifier.

Chao, can you also put this under a new CONFIG such as "bool MEMFD_OPS", 
and select it from KVM?

Thanks,

Paolo