From 7ee3fa3365a94f1e81b4ede5029d14ca1f155617 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Tue, 13 Apr 2021 15:47:40 +0000
Subject: KVM: VMX: Don't use vcpu->run->internal.ndata as an array index

From: Reiji Watanabe <reijiw@google.com>

[ Upstream commit 04c4f2ee3f68c9a4bf1653d15f1a9a435ae33f7a ]

__vmx_handle_exit() uses vcpu->run->internal.ndata as an index for
an array access.  Since vcpu->run is (can be) mapped to a user address
space with a writer permission, the 'ndata' could be updated by the
user process at anytime (the user process can set it to outside the
bounds of the array).
So, it is not safe that __vmx_handle_exit() uses the 'ndata' that way.

Fixes: 1aa561b1a4c0 ("kvm: x86: Add "last CPU" to some KVM_EXIT information")
Signed-off-by: Reiji Watanabe <reijiw@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Message-Id: <20210413154739.490299-1-reijiw@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/vmx/vmx.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 880a2617820c..95f836fbceb2 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5986,19 +5986,19 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
 	     exit_reason.basic != EXIT_REASON_PML_FULL &&
 	     exit_reason.basic != EXIT_REASON_APIC_ACCESS &&
 	     exit_reason.basic != EXIT_REASON_TASK_SWITCH)) {
+		int ndata = 3;
+
 		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
 		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_DELIVERY_EV;
-		vcpu->run->internal.ndata = 3;
 		vcpu->run->internal.data[0] = vectoring_info;
 		vcpu->run->internal.data[1] = exit_reason.full;
 		vcpu->run->internal.data[2] = vcpu->arch.exit_qualification;
 		if (exit_reason.basic == EXIT_REASON_EPT_MISCONFIG) {
-			vcpu->run->internal.ndata++;
-			vcpu->run->internal.data[3] =
+			vcpu->run->internal.data[ndata++] =
 				vmcs_read64(GUEST_PHYSICAL_ADDRESS);
 		}
-		vcpu->run->internal.data[vcpu->run->internal.ndata++] =
-			vcpu->arch.last_vmentry_cpu;
+		vcpu->run->internal.data[ndata++] = vcpu->arch.last_vmentry_cpu;
+		vcpu->run->internal.ndata = ndata;
 		return 0;
 	}
 
-- 
2.30.2