Re: [PATCH v3 05/10] KVM: s390: Add optional storage key checking to MEMOP IOCTL

[Janis Schoetterl-Glausch <scgl@linux.ibm.com>]

On 2/10/22 10:29, Christian Borntraeger wrote:
> Am 09.02.22 um 18:04 schrieb Janis Schoetterl-Glausch:
>> User space needs a mechanism to perform key checked accesses when
>> emulating instructions.
>>
>> The key can be passed as an additional argument.
>> Having an additional argument is flexible, as user space can
>> pass the guest PSW's key, in order to make an access the same way the
>> CPU would, or pass another key if necessary.
>>
>> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
>> Acked-by: Janosch Frank <frankja@linux.ibm.com>
>> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> 
> Claudio, Janosch, can you confirm that this is still valid?
> 
> 
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>

Not @linux.ibm.com?
> 
> minor thing below
>> ---
>>   arch/s390/kvm/kvm-s390.c | 30 ++++++++++++++++++++----------
>>   include/uapi/linux/kvm.h |  6 +++++-
>>   2 files changed, 25 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index cf347e1a4f17..85763ec7bc60 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -32,6 +32,7 @@
>>   #include <linux/sched/signal.h>
>>   #include <linux/string.h>
>>   #include <linux/pgtable.h>
>> +#include <linux/bitfield.h>
> 
> do we still need that after the changes?

No, not since we moved the key out of the flags.
> 
>>     #include <asm/asm-offsets.h>
>>   #include <asm/lowcore.h>
>> @@ -2359,6 +2360,11 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
>>       return r;
>>   }
>>   +static bool access_key_invalid(u8 access_key)
>> +{
>> +    return access_key > 0xf;
>> +}
>> +
>>   long kvm_arch_vm_ioctl(struct file *filp,
>>                  unsigned int ioctl, unsigned long arg)
>>   {
>> @@ -4690,17 +4696,19 @@ static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
>>       void *tmpbuf = NULL;
>>       int r = 0;
>>       const u64 supported_flags = KVM_S390_MEMOP_F_INJECT_EXCEPTION
>> -                    | KVM_S390_MEMOP_F_CHECK_ONLY;
>> +                    | KVM_S390_MEMOP_F_CHECK_ONLY
>> +                    | KVM_S390_MEMOP_F_SKEY_PROTECTION;
>>         if (mop->flags & ~supported_flags || mop->ar >= NUM_ACRS || !mop->size)
>>           return -EINVAL;
>> -
>>       if (mop->size > MEM_OP_MAX_SIZE)
>>           return -E2BIG;
>> -
>>       if (kvm_s390_pv_cpu_is_protected(vcpu))
>>           return -EINVAL;
>> -
>> +    if (mop->flags & KVM_S390_MEMOP_F_SKEY_PROTECTION) {
>> +        if (access_key_invalid(mop->key))
>> +            return -EINVAL;
>> +    }
>>       if (!(mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)) {
>>           tmpbuf = vmalloc(mop->size);
>>           if (!tmpbuf)
>> @@ -4710,11 +4718,12 @@ static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
>>       switch (mop->op) {
>>       case KVM_S390_MEMOP_LOGICAL_READ:
>>           if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
>> -            r = check_gva_range(vcpu, mop->gaddr, mop->ar,
>> -                        mop->size, GACC_FETCH, 0);
>> +            r = check_gva_range(vcpu, mop->gaddr, mop->ar, mop->size,
>> +                        GACC_FETCH, mop->key);
>>               break;
>>           }
>> -        r = read_guest(vcpu, mop->gaddr, mop->ar, tmpbuf, mop->size);
>> +        r = read_guest_with_key(vcpu, mop->gaddr, mop->ar, tmpbuf,
>> +                    mop->size, mop->key);
>>           if (r == 0) {
>>               if (copy_to_user(uaddr, tmpbuf, mop->size))
>>                   r = -EFAULT;
>> @@ -4722,15 +4731,16 @@ static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
>>           break;
>>       case KVM_S390_MEMOP_LOGICAL_WRITE:
>>           if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
>> -            r = check_gva_range(vcpu, mop->gaddr, mop->ar,
>> -                        mop->size, GACC_STORE, 0);
>> +            r = check_gva_range(vcpu, mop->gaddr, mop->ar, mop->size,
>> +                        GACC_STORE, mop->key);
>>               break;
>>           }
>>           if (copy_from_user(tmpbuf, uaddr, mop->size)) {
>>               r = -EFAULT;
>>               break;
>>           }
>> -        r = write_guest(vcpu, mop->gaddr, mop->ar, tmpbuf, mop->size);
>> +        r = write_guest_with_key(vcpu, mop->gaddr, mop->ar, tmpbuf,
>> +                     mop->size, mop->key);
>>           break;
>>       }
>>   diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index b46bcdb0cab1..44558cf4c52e 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -562,7 +562,10 @@ struct kvm_s390_mem_op {
>>       __u32 op;        /* type of operation */
>>       __u64 buf;        /* buffer in userspace */
>>       union {
>> -        __u8 ar;    /* the access register number */
>> +        struct {
>> +            __u8 ar;    /* the access register number */
>> +            __u8 key;    /* access key, ignored if flag unset */
>> +        };
>>           __u32 sida_offset; /* offset into the sida */
>>           __u8 reserved[32]; /* should be set to 0 */
>>       };
>> @@ -575,6 +578,7 @@ struct kvm_s390_mem_op {
>>   /* flags for kvm_s390_mem_op->flags */
>>   #define KVM_S390_MEMOP_F_CHECK_ONLY        (1ULL << 0)
>>   #define KVM_S390_MEMOP_F_INJECT_EXCEPTION    (1ULL << 1)
>> +#define KVM_S390_MEMOP_F_SKEY_PROTECTION    (1ULL << 2)
>>     /* for KVM_INTERRUPT */
>>   struct kvm_interrupt {