Re: [PATCH v5 2/8] s390/sclp: rework sclp boundary checks

[Collin Walling]

On 9/11/20 6:24 AM, Cornelia Huck wrote:
> On Thu, 10 Sep 2020 19:45:01 +0200
> Thomas Huth <thuth@redhat.com> wrote:
> 
>> On 10/09/2020 11.36, Collin Walling wrote:
>>> Rework the SCLP boundary check to account for different SCLP commands
>>> (eventually) allowing different boundary sizes.
>>>
>>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>>> Acked-by: Janosch Frank <frankja@linux.ibm.com>
>>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>>> ---
>>>  hw/s390x/sclp.c | 19 ++++++++++++++++++-
>>>  1 file changed, 18 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>>> index 28b973de8f..69a8724dc7 100644
>>> --- a/hw/s390x/sclp.c
>>> +++ b/hw/s390x/sclp.c
>>> @@ -49,6 +49,18 @@ static inline bool sclp_command_code_valid(uint32_t code)
>>>      return false;
>>>  }
>>>  
>>> +static bool sccb_verify_boundary(uint64_t sccb_addr, uint16_t len)  
>>
>> Maybe it would be good to add a comment in front of the function to say
>> that len must be big endian?
> 
> What about renaming it to sccb_h_len or so? That would make it more
> clear that the parameter is not just some random length.
> 

I think that makes sense.

>>
>>  Thomas
>>
>>> +{
>>> +    uint64_t sccb_max_addr = sccb_addr + be16_to_cpu(len) - 1;
>>> +    uint64_t sccb_boundary = (sccb_addr & PAGE_MASK) + PAGE_SIZE;
>>> +
>>> +    if (sccb_max_addr < sccb_boundary) {
>>> +        return true;
>>> +    }
>>> +
>>> +    return false;
>>> +}
>>> +
>>>  static void prepare_cpu_entries(MachineState *ms, CPUEntry *entry, int 
>>> *count)
>>>  {
>>>      uint8_t features[SCCB_CPU_FEATURE_LEN] = { 0 };
>>> @@ -229,6 +241,11 @@ int sclp_service_call_protected(CPUS390XState *env, 
>>> uint64_t sccb,
>>>          goto out_write;
>>>      }
>>>  
>>> +    if (!sccb_verify_boundary(sccb, work_sccb.h.length)) {
> 
> ...name inspired by the 'h' in here.
> 
>>> +        work_sccb.h.response_code = 
>>> cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
>>> +        goto out_write;
>>> +    }
>>> +
>>>      sclp_c->execute(sclp, &work_sccb, code);
>>>  out_write:
>>>      s390_cpu_pv_mem_write(env_archcpu(env), 0, &work_sccb,
>>> @@ -274,7 +291,7 @@ int sclp_service_call(CPUS390XState *env, uint64_t 
>>> sccb, uint32_t code)
>>>          goto out_write;
>>>      }
>>>  
>>> -    if ((sccb + be16_to_cpu(work_sccb.h.length)) > ((sccb & PAGE_MASK) + 
>>> PAGE_SIZE)) {
>>> +    if (!sccb_verify_boundary(sccb, work_sccb.h.length)) {
>>>          work_sccb.h.response_code = 
>>> cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
>>>          goto out_write;
>>>      }
>>>   
>>
> 
> 


-- 
Regards,
Collin

Stay safe and stay healthy