linux-kernel - Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

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]

Message-ID: <b2743a3a-a1b4-2d2e-98be-87b58ad387cf@redhat.com>
Date:   Tue, 23 Aug 2022 09:55:03 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Hugh Dickins <hughd@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
        linux-kselftest@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        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>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>, luto@...nel.org,
        jun.nakajima@...el.com, dave.hansen@...el.com, ak@...ux.intel.com,
        aarcange@...hat.com, ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        Muchun Song <songmuchun@...edance.com>,
        "Gupta, Pankaj" <pankaj.gupta@....com>
Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM
 guest private memory

On 19.08.22 05:38, Hugh Dickins wrote:
> On Fri, 19 Aug 2022, Sean Christopherson wrote:
>> On Thu, Aug 18, 2022, Kirill A . Shutemov wrote:
>>> On Wed, Aug 17, 2022 at 10:40:12PM -0700, Hugh Dickins wrote:
>>>> On Wed, 6 Jul 2022, Chao Peng wrote:
>>>> But since then, TDX in particular has forced an effort into preventing
>>>> (by flags, seals, notifiers) almost everything that makes it shmem/tmpfs.
>>>>
>>>> Are any of the shmem.c mods useful to existing users of shmem.c? No.
>>>> Is MFD_INACCESSIBLE useful or comprehensible to memfd_create() users? No.
>>
>> But QEMU and other VMMs are users of shmem and memfd.  The new features certainly
>> aren't useful for _all_ existing users, but I don't think it's fair to say that
>> they're not useful for _any_ existing users.
> 
> Okay, I stand corrected: there exist some users of memfd_create()
> who will also have use for "INACCESSIBLE" memory.

As raised in reply to the relevant patch, I'm not sure if we really have
to/want to expose MFD_INACCESSIBLE to user space. I feel like this is a
requirement of specific memfd_notifer (memfile_notifier) implementations
-- such as TDX that will convert the memory and MCE-kill the machine on
ordinary write access. We might be able to set/enforce this when
registering a notifier internally instead, and fail notifier
registration if a condition isn't met (e.g., existing mmap).

So I'd be curious, which other users of shmem/memfd would benefit from
(MMU)-"INACCESSIBLE" memory obtained via memfd_create()?

-- 
Thanks,

David / dhildenb