Re: [PATCH RFC 03/39] KVM: x86/xen: register shared_info page

[David Woodhouse]

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 = gfn_to_page(kvm, gfn);
> +       if (is_error_page(page))
> +               return -EINVAL;
> +
> +       kvm->arch.xen.shinfo_addr = gfn;
> +
> +       shared_info = page_to_virt(page);
> +       memset(shared_info, 0, sizeof(struct shared_info));
> +       kvm->arch.xen.shinfo = 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()?

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