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

Sean Christopherson
2021-04-22T02:21:43Z

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@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.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);