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@linux.intel.com>
Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/0ba029932a816179b9d14a30db38f0f11ef1f166.1594925782.git.pawan.kumar.gupta@linux.intel.com

diff --git a/Documentation/admin-guide/hw-vuln/multihit.rst b/Documentation/admin-guide/hw-vuln/multihit.rst
index ba9988d..140e4ce 100644 (file)
--- 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 (file)
--- 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");