Re: [PATCH v5 3/8] s390/sclp: read sccb from mem based on provided length

[Collin Walling <walling@linux.ibm.com>]

On 9/12/20 2:28 AM, Thomas Huth wrote:
> On 11/09/2020 20.16, Collin Walling wrote:
>> On 9/10/20 1:56 PM, Collin Walling wrote:
>>> On 9/10/20 1:50 PM, Thomas Huth wrote:
>>>> On 10/09/2020 11.36, Collin Walling wrote:
>>>>> The header contained within the SCCB passed to the SCLP service call
>>>>> contains the actual length of the SCCB. Instead of allocating a static
>>>>> 4K size for the work sccb, let's allow for a variable size determined
>>>>> by the value in the header. The proper checks are already in place to
>>>>> ensure the SCCB length is sufficent to store a full response and that
>>>>> the length does not cross any explicitly-set boundaries.
>>>>>
>>>>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>>>>> ---
>>>>>  hw/s390x/event-facility.c |  2 +-
>>>>>  hw/s390x/sclp.c           | 58 ++++++++++++++++++++++-----------------
>>>>>  include/hw/s390x/sclp.h   |  2 +-
>>>>>  3 files changed, 35 insertions(+), 27 deletions(-)
>>>>>
>>>>> diff --git a/hw/s390x/event-facility.c b/hw/s390x/event-facility.c
>>>>> index 645b4080c5..ed92ce510d 100644
>>>>> --- a/hw/s390x/event-facility.c
>>>>> +++ b/hw/s390x/event-facility.c
>>>>> @@ -213,7 +213,7 @@ static uint16_t handle_sccb_read_events(SCLPEventFacility *ef, SCCB *sccb,
>>>>>  
>>>>>      event_buf = &red->ebh;
>>>>>      event_buf->length = 0;
>>>>> -    slen = sizeof(sccb->data);
>>>>> +    slen = sccb_data_len(sccb);
>>>>>  
>>>>>      rc = SCLP_RC_NO_EVENT_BUFFERS_STORED;
>>>>>  
>>>>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>>>>> index 69a8724dc7..cb8e2e8ec3 100644
>>>>> --- a/hw/s390x/sclp.c
>>>>> +++ b/hw/s390x/sclp.c
>>>>> @@ -231,25 +231,30 @@ int sclp_service_call_protected(CPUS390XState *env, uint64_t sccb,
>>>>>  {
>>>>>      SCLPDevice *sclp = get_sclp_device();
>>>>>      SCLPDeviceClass *sclp_c = SCLP_GET_CLASS(sclp);
>>>>> -    SCCB work_sccb;
>>>>> -    hwaddr sccb_len = sizeof(SCCB);
>>>>> +    SCCBHeader header;
>>>>> +    SCCB *work_sccb;
>>>>
>>>> I'd maybe use "g_autofree SCCB *work_sccb = NULL" so you don't have to
>>>> worry about doing the g_free() later.
>>>
>>> Can do.
>>>
>>>>
>>>>> -    s390_cpu_pv_mem_read(env_archcpu(env), 0, &work_sccb, sccb_len);
>>>>> +    s390_cpu_pv_mem_read(env_archcpu(env), 0, &header, sizeof(SCCBHeader));
>>>>> +
>>>>> +    work_sccb = g_malloc0(header.length);
>>>>
>>>> Please use be16_to_cpu(header.length) here as well.
>>>
>>> Good catch, thanks!
>>>
>>
>> Shouldn't the mallocs use cpu_to_be16 instead since the header length
>> was read in from a cpu?
> 
> Now you confuse me ... s390x is big endian, so to get a usable value, we
> have to convert big-endian to the host byte order, not the other way
> round, don't we?
> 
>  Thomas
> 
> 

Err, yes you're right.

-- 
Regards,
Collin

Stay safe and stay healthy