From: Ankur Arora <ankur.a.arora@oracle.com>
To: David Woodhouse <dwmw2@infradead.org>,
Joao Martins <joao.m.martins@oracle.com>
Cc: "Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <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, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org
Subject: Re: [PATCH RFC 03/39] KVM: x86/xen: register shared_info page
Date: Wed, 2 Dec 2020 12:32:11 -0800 [thread overview]
Message-ID: <6ea92fe2-4067-d0e0-b716-16d39a7a6065@oracle.com> (raw)
In-Reply-To: <58db65203b9464f6f225f4ef97c45af3c72cf068.camel@infradead.org>
On 2020-12-02 4:20 a.m., David Woodhouse wrote:
> On Wed, 2020-12-02 at 10:44 +0000, Joao Martins wrote:
>> [late response - was on holiday yesterday]
>>
>> On 12/2/20 12:40 AM, Ankur Arora wrote:
>>> On 2020-12-01 5:07 a.m., David Woodhouse wrote:
>>>> 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?
>>>
>>> So looking at my WIP trees from the time, this is something that
>>> we went back and forth on as well with using just a pinned page or a
>>> persistent kvm_vcpu_map().
>>>
>>> I remember distinguishing shared_info/vcpu_info from kvm_setup_pvclock_page()
>>> as shared_info is created early and is not expected to change during the
>>> lifetime of the guest which didn't seem true for MSR_KVM_SYSTEM_TIME (or
>>> MSR_KVM_STEAL_TIME) so that would either need to do a kvm_vcpu_map()
>>> kvm_vcpu_unmap() dance or do some kind of synchronization.
>>>
>>> That said, I don't think this code explicitly disallows any updates
>>> to shared_info.
>>>
>>>>
>>>> If that was allowed, wouldn't it have been a much simpler fix for
>>>> CVE-2019-3016? What am I missing?
>>>
>>> Agreed.
>>>
>>> Perhaps, Paolo can chime in with why KVM never uses pinned page
>>> and always prefers to do cached mappings instead?
>>>
>>
>> Part of the CVE fix to not use cached versions.
>>
>> It's not a longterm pin of the page unlike we try to do here (partly due to the nature
>> of the pages we are mapping) but we still we map the gpa, RMW the steal time struct, and
>> then unmap the page.
>>
>> See record_steal_time() -- but more specifically commit b043138246 ("x86/KVM: Make sure
>> KVM_VCPU_FLUSH_TLB flag is not missed").
>>
>> But I am not sure it's a good idea to follow the same as record_steal_time() given that
>> this is a fairly sensitive code path for event channels.
>
> Right. We definitely need to use atomic RMW operations (like the CVE
> fix did) so the page needs to be *mapped*.
>
> My question was about a permanent pinned mapping vs the map/unmap as we
> need it that record_steal_time() does.
>
> On IRC, Paolo told me that permanent pinning causes problems for memory
> hotplug, and pointed me at the trick we do with an MMU notifier and
> kvm_vcpu_reload_apic_access_page().
Okay that answers my question. Thanks for clearing that up.
Not sure of a good place to document this but it would be good to
have this written down somewhere. Maybe kvm_map_gfn()?
>
> I'm going to stick with the pinning we have for the moment, and just
> fix up the fact that it leaks the pinned pages if the guest sets the
> shared_info address more than once.
>
> At some point the apic page MMU notifier thing can be made generic, and
> we can use that for this and for KVM steal time too.
>
Yeah, that's something that'll definitely be good to have.
Ankur
next prev parent reply other threads:[~2020-12-02 20:33 UTC|newest]
Thread overview: 126+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-20 20:15 [PATCH RFC 00/39] x86/KVM: Xen HVM guest support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 01/39] KVM: x86: fix Xen hypercall page msr handling Joao Martins
2019-02-22 1:30 ` Sean Christopherson
2019-02-22 11:47 ` Joao Martins
2019-02-22 12:51 ` Paolo Bonzini
2020-11-30 10:39 ` David Woodhouse
2020-11-30 11:03 ` Paolo Bonzini
2020-11-30 11:27 ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 02/39] KVM: x86/xen: intercept xen hypercalls if enabled Joao Martins
2019-02-21 18:29 ` Sean Christopherson
2019-02-21 20:56 ` Joao Martins
2019-02-22 0:30 ` Sean Christopherson
2019-02-22 12:50 ` Paolo Bonzini
2020-12-01 9:48 ` David Woodhouse
2020-12-01 11:19 ` David Woodhouse
2020-12-02 11:17 ` Joao Martins
2020-12-02 12:12 ` David Woodhouse
2020-12-02 5:19 ` Ankur Arora
2020-12-02 8:03 ` David Woodhouse
2020-12-02 18:20 ` Ankur Arora
2019-02-20 20:15 ` [PATCH RFC 03/39] KVM: x86/xen: register shared_info page Joao Martins
2020-12-01 13:07 ` David Woodhouse
2020-12-02 0:40 ` Ankur Arora
2020-12-02 1:26 ` David Woodhouse
2020-12-02 5:17 ` Ankur Arora
2020-12-02 10:50 ` Joao Martins
2020-12-02 10:44 ` Joao Martins
2020-12-02 12:20 ` David Woodhouse
2020-12-02 20:32 ` Ankur Arora [this message]
2020-12-03 10:16 ` David Woodhouse
2020-12-04 17:30 ` Sean Christopherson
2020-12-02 20:33 ` Ankur Arora
2020-12-12 12:07 ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 04/39] KVM: x86/xen: setup pvclock updates Joao Martins
2019-02-20 20:15 ` [PATCH RFC 05/39] KVM: x86/xen: update wallclock region Joao Martins
2019-02-20 20:15 ` [PATCH RFC 06/39] KVM: x86/xen: register vcpu info Joao Martins
2019-02-20 20:15 ` [PATCH RFC 07/39] KVM: x86/xen: register vcpu time info region Joao Martins
2019-02-20 20:15 ` [PATCH RFC 08/39] KVM: x86/xen: register steal clock Joao Martins
2019-02-20 20:15 ` [PATCH RFC 09/39] KVM: x86: declare Xen HVM guest capability Joao Martins
2019-02-20 20:15 ` [PATCH RFC 10/39] KVM: x86/xen: support upcall vector Joao Martins
2020-12-02 11:17 ` David Woodhouse
2020-12-02 13:12 ` Joao Martins
2020-12-02 16:47 ` David Woodhouse
2020-12-02 18:34 ` Joao Martins
2020-12-02 19:02 ` David Woodhouse
2020-12-02 20:12 ` Joao Martins
2020-12-02 20:37 ` David Woodhouse
2020-12-03 1:08 ` Ankur Arora
2020-12-08 16:08 ` David Woodhouse
2020-12-09 6:35 ` Ankur Arora
2020-12-09 10:27 ` David Woodhouse
2020-12-09 10:51 ` Joao Martins
2020-12-09 11:39 ` David Woodhouse
2020-12-09 13:26 ` Joao Martins
2020-12-09 15:41 ` David Woodhouse
2020-12-09 16:12 ` Joao Martins
2021-01-01 14:33 ` David Woodhouse
2021-01-05 12:11 ` Joao Martins
2021-01-05 13:23 ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 11/39] KVM: x86/xen: evtchn signaling via eventfd Joao Martins
2020-11-30 9:41 ` David Woodhouse
2020-11-30 12:17 ` Joao Martins
2020-11-30 12:55 ` David Woodhouse
2020-11-30 15:08 ` Joao Martins
2020-11-30 16:48 ` David Woodhouse
2020-11-30 17:15 ` Joao Martins
2020-11-30 18:01 ` David Woodhouse
2020-11-30 18:41 ` Joao Martins
2020-11-30 19:04 ` David Woodhouse
2020-11-30 19:25 ` Joao Martins
2021-11-23 13:15 ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 12/39] KVM: x86/xen: store virq when assigning evtchn Joao Martins
[not found] ` <b750291466f3c89e0a393e48079c087704b217a5.camel@amazon.co.uk>
2022-02-10 12:17 ` Joao Martins
2022-02-10 15:23 ` [EXTERNAL] " David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 13/39] KVM: x86/xen: handle PV timers oneshot mode Joao Martins
2019-02-20 20:15 ` [PATCH RFC 14/39] KVM: x86/xen: handle PV IPI vcpu yield Joao Martins
2019-02-20 20:15 ` [PATCH RFC 15/39] KVM: x86/xen: handle PV spinlocks slowpath Joao Martins
2022-02-08 12:36 ` David Woodhouse
2022-02-10 12:17 ` Joao Martins
2022-02-10 14:11 ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 16/39] KVM: x86: declare Xen HVM evtchn offload capability Joao Martins
2019-02-20 20:15 ` [PATCH RFC 17/39] x86/xen: export vcpu_info and shared_info Joao Martins
2019-02-20 20:15 ` [PATCH RFC 18/39] x86/xen: make hypercall_page generic Joao Martins
2019-02-20 20:15 ` [PATCH RFC 19/39] xen/xenbus: xenbus uninit support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 20/39] xen-blkback: module_exit support Joao Martins
2019-02-25 18:57 ` Konrad Rzeszutek Wilk
2019-02-26 11:20 ` Joao Martins
2019-02-20 20:15 ` [PATCH RFC 21/39] KVM: x86/xen: domid allocation Joao Martins
2019-02-20 20:15 ` [PATCH RFC 22/39] KVM: x86/xen: grant table init Joao Martins
2019-02-20 20:15 ` [PATCH RFC 23/39] KVM: x86/xen: grant table grow support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 24/39] KVM: x86/xen: backend hypercall support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 25/39] KVM: x86/xen: grant map support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 26/39] KVM: x86/xen: grant unmap support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 27/39] KVM: x86/xen: grant copy support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 28/39] KVM: x86/xen: interdomain evtchn support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 29/39] KVM: x86/xen: evtchn unmask support Joao Martins
2019-02-20 20:16 ` [PATCH RFC 30/39] KVM: x86/xen: add additional evtchn ops Joao Martins
2019-02-20 20:16 ` [PATCH RFC 31/39] xen-shim: introduce shim domain driver Joao Martins
2019-02-20 20:16 ` [PATCH RFC 32/39] xen/balloon: xen_shim_domain() support Joao Martins
2019-02-20 20:16 ` [PATCH RFC 33/39] xen/grant-table: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 34/39] xen/gntdev: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 35/39] xen/xenbus: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 36/39] drivers/xen: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 37/39] xen-netback: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 38/39] xen-blkback: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 39/39] KVM: x86: declare Xen HVM Dom0 capability Joao Martins
2019-02-20 21:09 ` [PATCH RFC 00/39] x86/KVM: Xen HVM guest support Paolo Bonzini
2019-02-21 0:29 ` Ankur Arora
2019-02-21 11:45 ` Joao Martins
2019-02-22 16:59 ` Paolo Bonzini
2019-03-12 17:14 ` Joao Martins
2019-04-08 6:44 ` Juergen Gross
2019-04-08 10:36 ` Joao Martins
2019-04-08 10:42 ` Juergen Gross
2019-04-08 17:31 ` Joao Martins
2019-04-09 0:35 ` Stefano Stabellini
2019-04-10 5:50 ` [Xen-devel] " Ankur Arora
2019-04-10 20:45 ` Stefano Stabellini
2019-04-09 5:04 ` Juergen Gross
2019-04-10 6:55 ` Ankur Arora
2019-04-10 7:14 ` Juergen Gross
2019-02-20 23:39 ` [Xen-devel] " Marek Marczykowski-Górecki
2019-02-21 0:31 ` Ankur Arora
2019-02-21 7:57 ` Juergen Gross
2019-02-21 12:00 ` Joao Martins
2019-02-21 11:55 ` Joao Martins
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