linux-kernel - [PATCH 1/7] KVM: x86: Short-circuit all kvm_lapic_set

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20241009181742.1128779-2-seanjc@google.com>
Date: Wed,  9 Oct 2024 11:17:35 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/7] KVM: x86: Short-circuit all kvm_lapic_set_base() if MSR
 value isn't changing

Do nothing in kvm_lapic_set_base() if the APIC base MSR value is the same
as the current value.  All flows except the handling of the base address
explicitly take effect if and only if relevant bits are changing.

For the base address, invoking kvm_lapic_set_base() before KVM initializes
the base to APIC_DEFAULT_PHYS_BASE during vCPU RESET would be a KVM bug,
i.e. KVM _must_ initialize apic->base_address before exposing the vCPU (to
userspace or KVM at-large).

Note, the inhibit is intended to be set if the base address is _changed_
from the default, i.e. is also covered by the RESET behavior.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/lapic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 2098dc689088..ffccd6e7e5c1 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2582,6 +2582,9 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
 	u64 old_value = vcpu->arch.apic_base;
 	struct kvm_lapic *apic = vcpu->arch.apic;

+	if (old_value == value)
+		return;
+
 	vcpu->arch.apic_base = value;

 	if ((old_value ^ value) & MSR_IA32_APICBASE_ENABLE)
-- 
2.47.0.rc1.288.g06298d1525-goog