Re: [PATCH] KVM: x86: restrict maximal physical address
From: Radim KrÄmÃÅ
Date: Fri Nov 25 2016 - 11:57:57 EST
2016-11-25 17:10+0100, Paolo Bonzini:
> On 25/11/2016 15:51, Radim KrÄmÃÅ wrote:
>> The guest could have configured a maximal physical address that exceeds
>> the host. Prevent that situation as it could easily lead to a bug.
>> Signed-off-by: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
>> arch/x86/kvm/cpuid.c | 8 +++++++-
>> 1 file changed, 7 insertions(+), 1 deletion(-)
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index 25f0f15fab1a..aed910e9fbed 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -136,7 +136,13 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>> ((best->eax & 0xff00) >> 8) != 0)
>> return -EINVAL;
>> - /* Update physical-address width */
>> + /*
>> + * Update physical-address width.
>> + * Make sure that it does not exceed hardware capabilities.
>> + */
>> + if (cpuid_query_maxphyaddr(vcpu) > boot_cpu_data.x86_phys_bits)
>> + return -EINVAL;
>> vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
> Not possible unfortunately, this would break most versions of QEMU that
> hard-code 40 for MAXPHYADDR.
> Also, "wider" physical addresses in the guest are actually possible with
> shadow paging.
We don't disable EPT in that case, though. I guess that situations
where QEMU configures mem slot into high physical addresses are not hit
in production ...
Is any solution better than ignoring this situation?