x86/bugs/multihit: Fix mitigation reporting when VMX is not in use (f29dfa53) · Commits · 戴 / test

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: ("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:

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

Documentation/admin-guide/hw-vuln/multihit.rst

+4 −0

Original line number	Diff line number	Diff line
		@@ -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

arch/x86/kernel/cpu/bugs.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -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");

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