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Commit ecb586bd authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Ingo Molnar
Browse files

KVM/x86: Remove indirect MSR op calls from SPEC_CTRL 



Having a paravirt indirect call in the IBRS restore path is not a
good idea, since we are trying to protect from speculative execution
of bogus indirect branch targets.  It is also slower, so use
native_wrmsrl() on the vmentry path too.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: default avatarJim Mattson <jmattson@google.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: KarimAllah Ahmed <karahmed@amazon.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kvm@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: d28b387f
Link: http://lkml.kernel.org/r/20180222154318.20361-2-pbonzini@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent d5028ba8

arch/x86/kvm/svm.c

+4 −3
Original line number Diff line number Diff line
@@ -49,6 +49,7 @@ 
#include <asm/debugreg.h>

#include <asm/kvm_para.h>

#include <asm/irq_remapping.h>

#include <asm/microcode.h>

#include <asm/nospec-branch.h>



#include <asm/virtext.h>
@@ -5355,7 +5356,7 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu) 
	 * being speculatively taken.

	 */

	if (svm->spec_ctrl)

		wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);

		native_wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);



	asm volatile (

		"push %%" _ASM_BP "; \n\t"
@@ -5465,10 +5466,10 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu) 
	 * save it.

	 */

	if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))

		rdmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);

		svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);



	if (svm->spec_ctrl)

		wrmsrl(MSR_IA32_SPEC_CTRL, 0);

		native_wrmsrl(MSR_IA32_SPEC_CTRL, 0);



	/* Eliminate branch target predictions from guest mode */

	vmexit_fill_RSB();

arch/x86/kvm/vmx.c

+4 −3
Original line number Diff line number Diff line
@@ -51,6 +51,7 @@ 
#include <asm/apic.h>

#include <asm/irq_remapping.h>

#include <asm/mmu_context.h>

#include <asm/microcode.h>

#include <asm/nospec-branch.h>



#include "trace.h"
@@ -9452,7 +9453,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) 
	 * being speculatively taken.

	 */

	if (vmx->spec_ctrl)

		wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);

		native_wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);



	vmx->__launched = vmx->loaded_vmcs->launched;

	asm(
@@ -9588,10 +9589,10 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) 
	 * save it.

	 */

	if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))

		rdmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);

		vmx->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);



	if (vmx->spec_ctrl)

		wrmsrl(MSR_IA32_SPEC_CTRL, 0);

		native_wrmsrl(MSR_IA32_SPEC_CTRL, 0);



	/* Eliminate branch target predictions from guest mode */

	vmexit_fill_RSB();