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

[Thomas Huth <thuth@redhat.com>]

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