CVE-2016-3713 kvm: out-of-bounds access in set_var_mtrr_msr (rhbz 1332139 1336410)

KVM-MTRR-remove-MSR-0x2f8.patch

@@ -0,0 +1,49 @@
+From bb0f06280beb6507226627a85076ae349a23fe22 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>
+Date: Mon, 16 May 2016 09:45:35 -0400
+Subject: [PATCH] KVM: MTRR: remove MSR 0x2f8
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+MSR 0x2f8 accessed the 124th Variable Range MTRR ever since MTRR support
+was introduced by 9ba075a664df ("KVM: MTRR support").
+
+0x2f8 became harmful when 910a6aae4e2e ("KVM: MTRR: exactly define the
+size of variable MTRRs") shrinked the array of VR MTRRs from 256 to 8,
+which made access to index 124 out of bounds.  The surrounding code only
+WARNs in this situation, thus the guest gained a limited read/write
+access to struct kvm_arch_vcpu.
+
+0x2f8 is not a valid VR MTRR MSR, because KVM has/advertises only 16 VR
+MTRR MSRs, 0x200-0x20f.  Every VR MTRR is set up using two MSRs, 0x2f8
+was treated as a PHYSBASE and 0x2f9 would be its PHYSMASK, but 0x2f9 was
+not implemented in KVM, therefore 0x2f8 could never do anything useful
+and getting rid of it is safe.
+
+This fixes CVE-2016-TBD.
+
+Fixes: 910a6aae4e2e ("KVM: MTRR: exactly define the size of variable MTRRs")
+Cc: stable@vger.kernel.org
+Reported-by: David Matlack <dmatlack@google.com>
+Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
+---
+ arch/x86/kvm/mtrr.c | 2 --
+ 1 file changed, 2 deletions(-)
+
+diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
+index 3f8c732117ec..c146f3c262c3 100644
+--- a/arch/x86/kvm/mtrr.c
++++ b/arch/x86/kvm/mtrr.c
+@@ -44,8 +44,6 @@ static bool msr_mtrr_valid(unsigned msr)
+ 	case MSR_MTRRdefType:
+ 	case MSR_IA32_CR_PAT:
+ 		return true;
+-	case 0x2f8:
+-		return true;
+ 	}
+ 	return false;
+ }
+-- 
+2.5.5
+

kernel.spec

@@ -619,6 +619,9 @@ Patch714: ALSA-timer-Fix-leak-in-SNDRV_TIMER_IOCTL_PARAMS.patch
 Patch715: ALSA-timer-Fix-leak-in-events-via-snd_timer_user_cca.patch
 Patch716: ALSA-timer-Fix-leak-in-events-via-snd_timer_user_tin.patch
 
+#CVE-2016-3713 rhbz 1332139 1336410
+Patch717: KVM-MTRR-remove-MSR-0x2f8.patch
+
 # END OF PATCH DEFINITIONS
 
 %endif
@@ -2146,6 +2149,7 @@ fi
 %changelog
 * Mon May 16 2016 Josh Boyer <jwboyer@fedoraproject.org> - 4.6.0-1
 - Linux v4.6
+- CVE-2016-3713 kvm: out-of-bounds access in set_var_mtrr_msr (rhbz 1332139 1336410)
 
 * Fri May 13 2016 Josh Boyer <jwboyer@fedoraproject.org> - 4.6.0-0.rc7.git3.1
 - Linux v4.6-rc7-116-ga2ccb68b1e6a