linux-kernel - [PATCH v2] x86/bugs/multihit: Fix mitigation reporting when VMX is not in use

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Message-ID: <0ba029932a816179b9d14a30db38f0f11ef1f166.1594925782.git.pawan.kumar.gupta@linux.intel.com>
Date:   Thu, 16 Jul 2020 12:23:59 -0700
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Jonathan Corbet <corbet@....net>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Tony Luck <tony.luck@...el.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        "Gomez Iglesias, Antonio" <antonio.gomez.iglesias@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Anthony Steinhauser <asteinhauser@...gle.com>,
        Waiman Long <longman@...hat.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Mark Gross <mgross@...ux.intel.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [PATCH v2] x86/bugs/multihit: Fix mitigation reporting when VMX is
 not in use

On systems that have virtualization disabled or unsupported, sysfs
mitigation for X86_BUG_ITLB_MULTIHIT is reported incorrectly as:

  $ cat /sys/devices/system/cpu/vulnerabilities/itlb_multihit
  KVM: Vulnerable

System is not vulnerable to DoS attack from a rogue guest when
virtualization is disabled or unsupported in the hardware. Change the
mitigation reporting for these cases.

Fixes: b8e8c8303ff2 ("kvm: mmu: ITLB_MULTIHIT mitigation")
Reported-by: Nelson Dsouza <nelson.dsouza@...ux.intel.com>
Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
---
v2:
 - Change mitigation reporting as per the state on VMX feature.

v1: https://lore.kernel.org/lkml/267631f4db4fd7e9f7ca789c2efaeab44103f68e.1594689154.git.pawan.kumar.gupta@linux.intel.com/

 Documentation/admin-guide/hw-vuln/multihit.rst | 4 ++++
 arch/x86/kernel/cpu/bugs.c                     | 8 +++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/hw-vuln/multihit.rst b/Documentation/admin-guide/hw-vuln/multihit.rst
index ba9988d8bce5..140e4cec38c3 100644
--- a/Documentation/admin-guide/hw-vuln/multihit.rst
+++ b/Documentation/admin-guide/hw-vuln/multihit.rst
@@ -80,6 +80,10 @@ The possible values in this file are:
        - The processor is not vulnerable.
      * - KVM: Mitigation: Split huge pages
        - Software changes mitigate this issue.
+     * - KVM: Mitigation: VMX unsupported
+       - KVM is not vulnerable because Virtual Machine Extensions (VMX) is not supported.
+     * - KVM: Mitigation: VMX disabled
+       - KVM is not vulnerable because Virtual Machine Extensions (VMX) is disabled.
      * - KVM: Vulnerable
        - The processor is vulnerable, but no mitigation enabled
 
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0b71970d2d3d..b0802d45abd3 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -31,6 +31,7 @@
 #include <asm/intel-family.h>
 #include <asm/e820/api.h>
 #include <asm/hypervisor.h>
+#include <asm/tlbflush.h>
 
 #include "cpu.h"
 
@@ -1556,7 +1557,12 @@ static ssize_t l1tf_show_state(char *buf)
 
 static ssize_t itlb_multihit_show_state(char *buf)
 {
-	if (itlb_multihit_kvm_mitigation)
+	if (!boot_cpu_has(X86_FEATURE_MSR_IA32_FEAT_CTL) ||
+	    !boot_cpu_has(X86_FEATURE_VMX))
+		return sprintf(buf, "KVM: Mitigation: VMX unsupported\n");
+	else if (!(cr4_read_shadow() & X86_CR4_VMXE))
+		return sprintf(buf, "KVM: Mitigation: VMX disabled\n");
+	else if (itlb_multihit_kvm_mitigation)
 		return sprintf(buf, "KVM: Mitigation: Split huge pages\n");
 	else
 		return sprintf(buf, "KVM: Vulnerable\n");
-- 
2.21.3