From ed129ec9057f89d615ba0c81a4984a90345a1684 Mon Sep 17 00:00:00 2001
From: Maxim Levitsky <mlevitsk@redhat.com>
Date: Thu, 3 Nov 2022 16:13:46 +0200
Subject: [PATCH 4/9] KVM: x86: forcibly leave nested mode on vCPU reset
Git-commit: ed129ec9057f89d615ba0c81a4984a90345a1684
Patch-mainline: v6.1-rc7
References: bsc#1204652 CVE-2022-3344
While not obivous, kvm_vcpu_reset() leaves the nested mode by clearing
'vcpu->arch.hflags' but it does so without all the required housekeeping.
On SVM, it is possible to have a vCPU reset while in guest mode because
unlike VMX, on SVM, INIT's are not latched in SVM non root mode and in
addition to that L1 doesn't have to intercept triple fault, which should
also trigger L1's reset if happens in L2 while L1 didn't intercept it.
If one of the above conditions happen, KVM will continue to use vmcb02
while not having in the guest mode.
Later the IA32_EFER will be cleared which will lead to freeing of the
nested guest state which will (correctly) free the vmcb02, but since
KVM still uses it (incorrectly) this will lead to a use after free
and kernel crash.
This issue is assigned CVE-2022-3344
Cc: stable@vger.kernel.org
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-id: <20221103141351.50662-5-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Vasant Karasulli <vkarasulli@suse.de>
---
arch/x86/kvm/x86.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ff5be7189237..597d7f804d72 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12003,7 +12003,17 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
unsigned long old_cr0 = kvm_read_cr0(vcpu);
+ /*
+ * SVM doesn't unconditionally VM-Exit on INIT and SHUTDOWN, thus it's
+ * possible to INIT the vCPU while L2 is active. Force the vCPU back
+ * into L1 as EFER.SVME is cleared on INIT (along with all other EFER
+ * bits), i.e. virtualization is disabled.
+ */
+ if (is_guest_mode(vcpu))
+ kvm_leave_nested(vcpu);
+
kvm_lapic_reset(vcpu, init_event);
+ WARN_ON_ONCE(is_guest_mode(vcpu) || is_smm(vcpu));
vcpu->arch.hflags = 0;
vcpu->arch.smi_pending = 0;
--
2.34.1