[PATCH 5.7 162/204] x86/bugs/multihit: Fix mitigation reporting when VMX is not in use

Greg Kroah-Hartman
2020-08-20T12:52:54Z

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>

[ Upstream commit f29dfa53cc8ae6ad93bae619bcc0bf45cab344f7 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 ba9988d8bce50..140e4cec38c33 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 b53dcff21438c..8c963ea39f9df 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");
--
2.25.1