linux-kernel - Re: [PATCH v2 1/2] KVM: s390: Disallow invalid bits in kvm_valid_regs and kvm_dirty

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Date:   Wed, 4 Sep 2019 11:11:22 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     David Hildenbrand <david@...hat.com>,
        Thomas Huth <thuth@...hat.com>, kvm@...r.kernel.org,
        Janosch Frank <frankja@...ux.ibm.com>
Cc:     Cornelia Huck <cohuck@...hat.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] KVM: s390: Disallow invalid bits in kvm_valid_regs
 and kvm_dirty_regs



On 04.09.19 11:05, David Hildenbrand wrote:
> On 04.09.19 10:51, Thomas Huth wrote:
>> If unknown bits are set in kvm_valid_regs or kvm_dirty_regs, this
>> clearly indicates that something went wrong in the KVM userspace
>> application. The x86 variant of KVM already contains a check for
>> bad bits, so let's do the same on s390x now, too.
>>
>> Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>
>> Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>
>> Reviewed-by: Cornelia Huck <cohuck@...hat.com>
>> Signed-off-by: Thomas Huth <thuth@...hat.com>
>> ---
>>  arch/s390/include/uapi/asm/kvm.h | 6 ++++++
>>  arch/s390/kvm/kvm-s390.c         | 4 ++++
>>  2 files changed, 10 insertions(+)
>>
>> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
>> index 47104e5b47fd..436ec7636927 100644
>> --- a/arch/s390/include/uapi/asm/kvm.h
>> +++ b/arch/s390/include/uapi/asm/kvm.h
>> @@ -231,6 +231,12 @@ struct kvm_guest_debug_arch {
>>  #define KVM_SYNC_GSCB   (1UL << 9)
>>  #define KVM_SYNC_BPBC   (1UL << 10)
>>  #define KVM_SYNC_ETOKEN (1UL << 11)
>> +
>> +#define KVM_SYNC_S390_VALID_FIELDS \
>> +	(KVM_SYNC_PREFIX | KVM_SYNC_GPRS | KVM_SYNC_ACRS | KVM_SYNC_CRS | \
>> +	 KVM_SYNC_ARCH0 | KVM_SYNC_PFAULT | KVM_SYNC_VRS | KVM_SYNC_RICCB | \
>> +	 KVM_SYNC_FPRS | KVM_SYNC_GSCB | KVM_SYNC_BPBC | KVM_SYNC_ETOKEN)
>> +
> 
> We didn't care about the S390 for the actual flags, why care now?

I think it makes sense to have the interface as defined as possible. If for some
reason userspace sets a wrong bit this would be undetected. If we at a later point
in time use that bit this would resultin strange problems.
> 
> 
>>  /* length and alignment of the sdnx as a power of two */
>>  #define SDNXC 8
>>  #define SDNXL (1UL << SDNXC)
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 49d7722229ae..a7d7dedfe527 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -3998,6 +3998,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>  	if (kvm_run->immediate_exit)
>>  		return -EINTR;
>>  
>> +	if (kvm_run->kvm_valid_regs & ~KVM_SYNC_S390_VALID_FIELDS ||
>> +	    kvm_run->kvm_dirty_regs & ~KVM_SYNC_S390_VALID_FIELDS)
>> +		return -EINVAL;
>> +
>>  	vcpu_load(vcpu);
>>  
>>  	if (guestdbg_exit_pending(vcpu)) {
>>
> 
> Reviewed-by: David Hildenbrand <david@...hat.com>
>