linux-kernel - [PATCH 3.16 134/192] kvm: nVMX: Don't allow L2 to access the hardware CR8

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Message-ID: <lsq.1507553065.965073498@decadent.org.uk>
Date:   Mon, 09 Oct 2017 13:44:25 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jim Mattson" <jmattson@...gle.com>,
        "David Hildenbrand" <david@...hat.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>
Subject: [PATCH 3.16 134/192] kvm: nVMX: Don't allow L2 to access the
 hardware CR8

3.16.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jim Mattson <jmattson@...gle.com>

commit 51aa68e7d57e3217192d88ce90fd5b8ef29ec94f upstream.

If L1 does not specify the "use TPR shadow" VM-execution control in
vmcs12, then L0 must specify the "CR8-load exiting" and "CR8-store
exiting" VM-execution controls in vmcs02. Failure to do so will give
the L2 VM unrestricted read/write access to the hardware CR8.

This fixes CVE-2017-12154.

Signed-off-by: Jim Mattson <jmattson@...gle.com>
Reviewed-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -8048,6 +8048,14 @@ static void prepare_vmcs02(struct kvm_vc
 	exec_control &= ~CPU_BASED_VIRTUAL_NMI_PENDING;
 	exec_control &= ~CPU_BASED_TPR_SHADOW;
 	exec_control |= vmcs12->cpu_based_vm_exec_control;
+
+ 	if (!(exec_control & CPU_BASED_TPR_SHADOW)) {
+#ifdef CONFIG_X86_64
+		exec_control |= CPU_BASED_CR8_LOAD_EXITING |
+				CPU_BASED_CR8_STORE_EXITING;
+#endif
+	}
+
 	/*
 	 * Merging of IO and MSR bitmaps not currently supported.
 	 * Rather, exit every time.