linux-kernel - [PATCH v2 2/9] KVM: x86: Check CR3 GPA for validity regardless of vCPU mode

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Message-Id: <20210422022128.3464144-3-seanjc@google.com>
Date:   Wed, 21 Apr 2021 19:21:21 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Babu Moger <babu.moger@....com>,
        Joao Martins <joao.m.martins@...cle.com>,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: [PATCH v2 2/9] KVM: x86: Check CR3 GPA for validity regardless of
 vCPU mode

Check CR3 for an invalid GPA even if the vCPU isn't in long mode.  For
bigger emulation flows, notably RSM, the vCPU mode may not be accurate
if CR0/CR4 are loaded after CR3.  For MOV CR3 and similar flows, the
caller is responsible for truncating the value.

Note, SMRAM.CR3 is read-only, so this is mostly a theoretical bug since
KVM will not have stored an illegal CR3 into SMRAM during SMI emulation.

Fixes: 660a5d517aaa ("KVM: x86: save/load state on SMM switch")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c9ba6f2d9bcd..63af93211871 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1078,10 +1078,15 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 		return 0;
 	}
 
-	if (is_long_mode(vcpu) && kvm_vcpu_is_illegal_gpa(vcpu, cr3))
+	/*
+	 * Do not condition the GPA check on long mode, this helper is used to
+	 * stuff CR3, e.g. for RSM emulation, and there is no guarantee that
+	 * the current vCPU mode is accurate.
+	 */
+	if (kvm_vcpu_is_illegal_gpa(vcpu, cr3))
 		return 1;
-	else if (is_pae_paging(vcpu) &&
-		 !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))
+
+	if (is_pae_paging(vcpu) && !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))
 		return 1;
 
 	kvm_mmu_new_pgd(vcpu, cr3, skip_tlb_flush, skip_tlb_flush);
-- 
2.31.1.498.g6c1eba8ee3d-goog