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Message-ID: <ZcMCogbbVKuTIXWJ@google.com>
Date: Tue, 6 Feb 2024 20:10:10 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paul Durrant <paul@....org>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>, David Woodhouse <dwmw2@...radead.org>, Shuah Khan <shuah@...nel.org>,
kvm@...r.kernel.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v12 11/20] KVM: xen: allow shared_info to be mapped by
fixed HVA
On Mon, Jan 15, 2024, Paul Durrant wrote:
> @@ -638,20 +637,32 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
> }
> break;
>
> - case KVM_XEN_ATTR_TYPE_SHARED_INFO: {
> + case KVM_XEN_ATTR_TYPE_SHARED_INFO:
> + case KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA: {
> int idx;
>
> mutex_lock(&kvm->arch.xen.xen_lock);
>
> idx = srcu_read_lock(&kvm->srcu);
>
> - if (data->u.shared_info.gfn == KVM_XEN_INVALID_GFN) {
> - kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
> - r = 0;
> + if (data->type == KVM_XEN_ATTR_TYPE_SHARED_INFO) {
> + if (data->u.shared_info.gfn == KVM_XEN_INVALID_GFN) {
> + kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
> + r = 0;
> + } else {
> + r = kvm_gpc_activate(&kvm->arch.xen.shinfo_cache,
> + gfn_to_gpa(data->u.shared_info.gfn),
> + PAGE_SIZE);
> + }
> } else {
> - r = kvm_gpc_activate(&kvm->arch.xen.shinfo_cache,
> - gfn_to_gpa(data->u.shared_info.gfn),
> - PAGE_SIZE);
> + if (data->u.shared_info.hva == 0) {
I know I said I don't care about the KVM Xen ABI, but I still think using '0' as
"invalid" is ridiculous.
More importantly, this code needs to check that HVA is a userspace pointer.
Because __kvm_set_memory_region() performs the address checks, KVM assumes any
hva that it gets out of a memslot, i.e. from a gfn, is a safe userspace address.
kvm_is_error_hva() will catch most addresses, but I'm pretty sure there's still
a small window where userspace could use this to write kernel memory.
> + kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
> + r = 0;
> + } else {
> + r = kvm_gpc_activate_hva(&kvm->arch.xen.shinfo_cache,
> + data->u.shared_info.hva,
> + PAGE_SIZE);
> + }
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