Commit 5104d7ff authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: VMX: Disable preemption when probing user return MSRs 



Disable preemption when probing a user return MSR via RDSMR/WRMSR.  If
the MSR holds a different value per logical CPU, the WRMSR could corrupt
the host's value if KVM is preempted between the RDMSR and WRMSR, and
then rescheduled on a different CPU.

Opportunistically land the helper in common x86, SVM will use the helper
in a future commit.

Fixes: 4be53410 ("KVM: VMX: Initialize vmx->guest_msrs[] right after allocation")
Cc: stable@vger.kernel.org
Cc: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-6-seanjc@google.com>
Reviewed-by: default avatarJim Mattson <jmattson@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 2183de41

arch/x86/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -1777,6 +1777,7 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low, 
		    unsigned long icr, int op_64_bit);



void kvm_define_user_return_msr(unsigned index, u32 msr);

int kvm_probe_user_return_msr(u32 msr);

int kvm_set_user_return_msr(unsigned index, u64 val, u64 mask);



u64 kvm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc);

arch/x86/kvm/vmx/vmx.c

+1 −4
Original line number Diff line number Diff line
@@ -6914,12 +6914,9 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu) 


	for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) {

		u32 index = vmx_uret_msrs_list[i];

		u32 data_low, data_high;

		int j = vmx->nr_uret_msrs;



		if (rdmsr_safe(index, &data_low, &data_high) < 0)

			continue;

		if (wrmsr_safe(index, data_low, data_high) < 0)

		if (kvm_probe_user_return_msr(index))

			continue;



		vmx->guest_uret_msrs[j].slot = i;

arch/x86/kvm/x86.c

+16 −0
Original line number Diff line number Diff line
@@ -339,6 +339,22 @@ static void kvm_on_user_return(struct user_return_notifier *urn) 
	}

}



int kvm_probe_user_return_msr(u32 msr)

{

	u64 val;

	int ret;



	preempt_disable();

	ret = rdmsrl_safe(msr, &val);

	if (ret)

		goto out;

	ret = wrmsrl_safe(msr, val);

out:

	preempt_enable();

	return ret;

}

EXPORT_SYMBOL_GPL(kvm_probe_user_return_msr);



void kvm_define_user_return_msr(unsigned slot, u32 msr)

{

	BUG_ON(slot >= KVM_MAX_NR_USER_RETURN_MSRS);