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

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

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?

[...]

-- 
Regards,
Collin

Stay safe and stay healthy