Commit f14eec0a authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: SVM: move more vmentry code to assembly 



Manipulate IF around vmload/vmsave to remove the confusing usage of
local_irq_enable where interrupts are actually disabled via GIF.
And stuff the RSB immediately without waiting for a RET to avoid
Spectre-v2 attacks.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 9ef1530c

arch/x86/include/asm/nospec-branch.h

+0 −21
Original line number Diff line number Diff line
@@ -237,27 +237,6 @@ enum ssb_mitigation { 
extern char __indirect_thunk_start[];

extern char __indirect_thunk_end[];



/*

 * On VMEXIT we must ensure that no RSB predictions learned in the guest

 * can be followed in the host, by overwriting the RSB completely. Both

 * retpoline and IBRS mitigations for Spectre v2 need this; only on future

 * CPUs with IBRS_ALL *might* it be avoided.

 */

static inline void vmexit_fill_RSB(void)

{

#ifdef CONFIG_RETPOLINE

	unsigned long loops;



	asm volatile (ANNOTATE_NOSPEC_ALTERNATIVE

		      ALTERNATIVE("jmp 910f",

				  __stringify(__FILL_RETURN_BUFFER(%0, RSB_CLEAR_LOOPS, %1)),

				  X86_FEATURE_RETPOLINE)

		      "910:"

		      : "=r" (loops), ASM_CALL_CONSTRAINT

		      : : "memory" );

#endif

}



static __always_inline

void alternative_msr_write(unsigned int msr, u64 val, unsigned int feature)

{

arch/x86/kvm/svm/svm.c

+0 −7
Original line number Diff line number Diff line
@@ -3330,13 +3330,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu) 
	 */

	x86_spec_ctrl_set_guest(svm->spec_ctrl, svm->virt_spec_ctrl);



	local_irq_enable();



	__svm_vcpu_run(svm->vmcb_pa, (unsigned long *)&svm->vcpu.arch.regs);



	/* Eliminate branch target predictions from guest mode */

	vmexit_fill_RSB();



#ifdef CONFIG_X86_64

	wrmsrl(MSR_GS_BASE, svm->host.gs_base);

#else
@@ -3366,8 +3361,6 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu) 


	reload_tss(vcpu);



	local_irq_disable();



	x86_spec_ctrl_restore_host(svm->spec_ctrl, svm->virt_spec_ctrl);



	vcpu->arch.cr2 = svm->vmcb->save.cr2;

arch/x86/kvm/svm/vmenter.S

+9 −0
Original line number Diff line number Diff line
@@ -3,6 +3,7 @@ 
#include <asm/asm.h>

#include <asm/bitsperlong.h>

#include <asm/kvm_vcpu_regs.h>

#include <asm/nospec-branch.h>



#define WORD_SIZE (BITS_PER_LONG / 8)
@@ -78,6 +79,7 @@ SYM_FUNC_START(__svm_vcpu_run) 
	pop %_ASM_AX



	/* Enter guest mode */

	sti

1:	vmload %_ASM_AX

	jmp 3f

2:	cmpb $0, kvm_rebooting
@@ -99,6 +101,13 @@ SYM_FUNC_START(__svm_vcpu_run) 
	ud2

	_ASM_EXTABLE(5b, 6b)

7:

	cli



#ifdef CONFIG_RETPOLINE

	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */

	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE

#endif



	/* "POP" @regs to RAX. */

	pop %_ASM_AX

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