From: Sean Christopherson <seanjc@google.com>
To: Maxim Levitsky <mlevitsk@redhat.com>
Cc: kvm@vger.kernel.org, Jim Mattson <jmattson@google.com>,
"H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Wanpeng Li <wanpengli@tencent.com>,
Borislav Petkov <bp@alien8.de>,
x86@kernel.org
Subject: Re: [PATCH 4/4] KVM: x86: lapic: don't allow to set non default apic id when not using x2apic api
Date: Thu, 3 Mar 2022 16:51:10 +0000 [thread overview]
Message-ID: <YiDx/uYAMSZDvobO@google.com> (raw)
In-Reply-To: <eae0b69fb8f5c47457fac853cc55b41a30762994.camel@redhat.com>
On Wed, Mar 02, 2022, Maxim Levitsky wrote:
> When APIC state is loading while APIC is in *x2apic* mode it does enforce that
> value in this 0x20 offset is initial apic id if KVM_CAP_X2APIC_API.
>
> I think that it is fair to also enforce this when KVM_CAP_X2APIC_API is not used,
> especially if we make apic id read-only.
I don't disagree in principle. But, (a) this loophole as existing for nearly 6
years, (b) closing the loophole could break userspace, (c) false positive are
possible due to truncation, and (d) KVM gains nothing meaningful by closing the
loophole.
(d) changes when we add a knob to make xAPIC ID read-only, but we can simply
require userspace to enable KVM_CAP_X2APIC_API (or force it). That approach
avoids (c) by eliminating truncation, and avoids (b) by virtue of being opt-in.
next prev parent reply other threads:[~2022-03-03 16:51 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-01 13:55 [PATCH 0/4] SVM fixes + apic fix Maxim Levitsky
2022-03-01 13:55 ` [PATCH 1/4] KVM: x86: mark synthetic SMM vmexit as SVM_EXIT_SW Maxim Levitsky
2022-03-01 16:31 ` Sean Christopherson
2022-03-01 17:13 ` Maxim Levitsky
2022-03-09 15:46 ` Paolo Bonzini
2022-03-01 13:55 ` [PATCH 2/4] KVM: x86: SVM: disable preemption in avic_refresh_apicv_exec_ctrl Maxim Levitsky
2022-03-01 17:15 ` Sean Christopherson
2022-03-01 17:20 ` Maxim Levitsky
2022-03-01 17:23 ` Paolo Bonzini
2022-03-01 13:55 ` [PATCH 3/4] KVM: x86: SVM: use vmcb01 in avic_init_vmcb Maxim Levitsky
2022-03-01 16:21 ` Sean Christopherson
2022-03-01 17:25 ` Maxim Levitsky
2022-03-01 17:35 ` Sean Christopherson
2022-03-09 15:48 ` Paolo Bonzini
2022-03-15 12:27 ` Maxim Levitsky
2022-03-01 13:55 ` [PATCH 4/4] KVM: x86: lapic: don't allow to set non default apic id when not using x2apic api Maxim Levitsky
2022-03-01 16:56 ` Sean Christopherson
2022-03-01 17:09 ` Maxim Levitsky
2022-03-01 17:46 ` Sean Christopherson
2022-03-01 17:56 ` Maxim Levitsky
2022-03-02 11:50 ` Maxim Levitsky
2022-03-03 16:51 ` Sean Christopherson [this message]
2022-03-03 18:15 ` Maxim Levitsky
2022-03-03 19:38 ` Sean Christopherson
2022-03-03 19:49 ` Sean Christopherson
2022-03-04 10:54 ` Maxim Levitsky
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