[PATCH 5.12 334/363] KVM: VMX: Disable preemption when probing user return MSRs

From: Greg Kroah-Hartman
Date: Mon May 17 2021 - 10:55:03 EST


From: Sean Christopherson <seanjc@xxxxxxxxxx>

commit 5104d7ffcf24749939bea7fdb5378d186473f890 upstream.

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: 4be534102624 ("KVM: VMX: Initialize vmx->guest_msrs[] right after allocation")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20210504171734.1434054-6-seanjc@xxxxxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/vmx/vmx.c | 5 +----
arch/x86/kvm/x86.c | 16 ++++++++++++++++
3 files changed, 18 insertions(+), 4 deletions(-)

--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1753,6 +1753,7 @@ int kvm_pv_send_ipi(struct kvm *kvm, uns
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);
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6914,12 +6914,9 @@ static int vmx_create_vcpu(struct kvm_vc

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;
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -335,6 +335,22 @@ static void kvm_on_user_return(struct us
}
}

+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);