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

Christian Borntraeger
2022-02-09T09:41:43Z

CC Konstantin,

I hope you can find the right people. Looks that my (and Janis) emaildid not make it to linux-s390 and kvm at vger lists.
Message-ID: <6ea27647-fbbe-3962-03a0-8ca5340fc7fd@linux.ibm.com>

Am 09.02.22 um 10:08 schrieb Christian Borntraeger:
>
>
> 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 :-)
>
>>>
>>>> +    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?
>
>> 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.
>>
>> [...]
>>