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

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Date:   Thu, 06 Aug 2020 18:50:13 -0000
From:   "tip-bot2 for Pawan Gupta" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Nelson Dsouza <nelson.dsouza@...ux.intel.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/urgent] x86/bugs/multihit: Fix mitigation reporting when
 VMX is not in use

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     31dccf7df081364045bff196bdc060ddda97f2e9
Gitweb:        https://git.kernel.org/tip/31dccf7df081364045bff196bdc060ddda97f2e9
Author:        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
AuthorDate:    Thu, 16 Jul 2020 12:23:59 -07:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Thu, 06 Aug 2020 19:04:51 +02:00

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>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Acked-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/r/0ba029932a816179b9d14a30db38f0f11ef1f166.1594925782.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 ba9988d..140e4ce 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 f0b743a..d3f0db4 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"
 
@@ -1549,7 +1550,12 @@ 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");