From: Sean Christopherson seanjc@google.com
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@vger.kernel.org Cc: Xiaoyao Li xiaoyao.li@intel.com Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20210504171734.1434054-6-seanjc@google.com Reviewed-by: Jim Mattson jmattson@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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);