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

Christian Borntraeger
2022-02-10T09:43:37Z

Am 10.02.22 um 10:40 schrieb Janis Schoetterl-Glausch:
> 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?

Yes, of course. Old habits...
Reviewed-by: Christian Borntraeger <borntraeger@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 {
>