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Message-ID: <b647bed6c75f8743b8afea251a88f00a5feaee29.camel@infradead.org>
Subject: Re: [PATCH RFC 03/39] KVM: x86/xen: register shared_info page
From:   David Woodhouse <dwmw2@infradead.org>
To:     Joao Martins <joao.m.martins@oracle.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Ankur Arora <ankur.a.arora@oracle.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org
Date:   Tue, 01 Dec 2020 13:07:23 +0000
In-Reply-To: <20190220201609.28290-4-joao.m.martins@oracle.com>
References: <20190220201609.28290-1-joao.m.martins@oracle.com>
         <20190220201609.28290-4-joao.m.martins@oracle.com>
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On Wed, 2019-02-20 at 20:15 +0000, Joao Martins wrote:
> +static int kvm_xen_shared_info_init(struct kvm *kvm, gfn_t gfn)
> +{
> +       struct shared_info *shared_info;
> +       struct page *page;
> +
> +       page =3D gfn_to_page(kvm, gfn);
> +       if (is_error_page(page))
> +               return -EINVAL;
> +
> +       kvm->arch.xen.shinfo_addr =3D gfn;
> +
> +       shared_info =3D page_to_virt(page);
> +       memset(shared_info, 0, sizeof(struct shared_info));
> +       kvm->arch.xen.shinfo =3D shared_info;
> +       return 0;
> +}
> +

Hm.

How come we get to pin the page and directly dereference it every time,
while kvm_setup_pvclock_page() has to use kvm_write_guest_cached()
instead?

If that was allowed, wouldn't it have been a much simpler fix for
CVE-2019-3016? What am I missing?

Should I rework these to use kvm_write_guest_cached()?=20


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