Re: [PATCH v2 05/11] KVM: s390: Add optional storage key checking to MEMOP IOCTL

Christian Borntraeger
2022-02-09T10:16:20Z

Am 09.02.22 um 11:01 schrieb Janis Schoetterl-Glausch:
> On Wed, 2022-02-09 at 10:08 +0100, Christian Borntraeger wrote:
>>
>> Am 09.02.22 um 09:49 schrieb Janis Schoetterl-Glausch:
>>> On 2/9/22 08:34, Christian Borntraeger wrote:
>>>> Am 07.02.22 um 17:59 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>
>>>>> ---
>>>>> arch/s390/kvm/kvm-s390.c | 49 +++++++++++++++++++++++++++++++---------
>>>>> include/uapi/linux/kvm.h | 8 +++++--
>>>>> 2 files changed, 44 insertions(+), 13 deletions(-)
>>>>>
>>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>>> index cf347e1a4f17..71e61fb3f0d9 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>
>>>>> #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)
>>>>> {
>>>>> @@ -4687,34 +4693,54 @@ static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
>>>>> struct kvm_s390_mem_op *mop)
>>>>> {
>>>>> void __user *uaddr = (void __user *)mop->buf;
>>>>> + u8 access_key = 0, ar = 0;
>>>>> void *tmpbuf = NULL;
>>>>> + bool check_reserved;
>>>>> 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)
>>>>> + if (mop->flags & ~supported_flags || !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_CHECK_ONLY)) {
>>>>> tmpbuf = vmalloc(mop->size);
>>>>> if (!tmpbuf)
>>>>> return -ENOMEM;
>>>>> }
>>>>> + ar = mop->ar;
>>>>> + mop->ar = 0;
>>>>
>>>> Why this assignment to 0?
>>>
>>> It's so the check of reserved below works like that, they're all part of the anonymous union.
>>
>> Ah, I see. This is ugly :-)
>
> Yes :)
>>
>>>>> + if (ar >= NUM_ACRS)
>>>>> + return -EINVAL;
>>>>> + if (mop->flags & KVM_S390_MEMOP_F_SKEY_PROTECTION) {
>>>>> + access_key = mop->key;
>>>>> + mop->key = 0;
>>>>
>>>> and this? I think we can leave mop unchanged.
>>>>
>>>> In fact, why do we add the ar and access_key variable?
>>>> This breaks the check from above (if (mop->flags & ~supported_flags || mop->ar >= NUM_ACRS || !mop->size)) into two checks
>>>> and it will create a memleak for tmpbuf.
>>>
>>> I can move the allocation down, goto out or get rid of the reserved check and keep everything as before.
>>> First is simpler, but second makes handling that case more explicit and might help in the future.
>>
>> Maybe add a reserved_02 field in the anon struct and check this for being zero and get rid of the local variables?
>
> I think that would require us adding new fields in the struct by putting them in a union with reserved_02 and so on,
> which could get rather messy.

I think it is fine to rename reserved_02. Maybe rename that to dont_use_02 ?
>
> Maybe a comment is good enought?
>>
>>> Patch 6 has the same issue in the vm ioctl handler.
>>>> Simply use mop->key and mop->ar below and get rid of the local variables.
>>>> The structure has no concurrency and gcc will handle that just as the local variable.
>>>>
>>>> Other than that this looks good.
>>>
>>> [...]
>>>
>