linux-kernel - [PATCH 5.14 052/172] KVM: x86: Clear KVMs cached guest CR3 at RESET/INIT

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Date:   Mon,  4 Oct 2021 14:51:42 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.14 052/172] KVM: x86: Clear KVMs cached guest CR3 at RESET/INIT

From: Sean Christopherson <seanjc@...gle.com>

commit 03a6e84069d1870f5b3d360e64cb330b66f76dee upstream.

Explicitly zero the guest's CR3 and mark it available+dirty at RESET/INIT.
Per Intel's SDM and AMD's APM, CR3 is zeroed at both RESET and INIT.  For
RESET, this is a nop as vcpu is zero-allocated.  For INIT, the bug has
likely escaped notice because no firmware/kernel puts its page tables root
at PA=0, let alone relies on INIT to get the desired CR3 for such page
tables.

Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Message-Id: <20210921000303.400537-3-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/x86.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10873,6 +10873,9 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcp
 
 	static_call(kvm_x86_vcpu_reset)(vcpu, init_event);
 
+	vcpu->arch.cr3 = 0;
+	kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
+
 	/*
 	 * Reset the MMU context if paging was enabled prior to INIT (which is
 	 * implied if CR0.PG=1 as CR0 will be '0' prior to RESET).  Unlike the