Re: [PATCH v1 3/8] s390/sclp: rework sclp boundary and length checks

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

On 5/12/20 3:21 AM, David Hildenbrand wrote:
> On 09.05.20 01:08, Collin Walling wrote:
>> Let's factor out the SCLP boundary and length checks
>> into separate functions.
>>
>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>> ---
>>   hw/s390x/sclp.c | 41 +++++++++++++++++++++++++++++++++++------
>>   1 file changed, 35 insertions(+), 6 deletions(-)
>>
>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>> index d08a291e40..470d5da7a2 100644
>> --- a/hw/s390x/sclp.c
>> +++ b/hw/s390x/sclp.c
>> @@ -49,6 +49,34 @@ static inline bool sclp_command_code_valid(uint32_t code)
>>       return false;
>>   }
>>   
>> +static bool check_sccb_boundary_valid(uint64_t sccb_addr, uint32_t code,
>> +                                      SCCB *sccb)
> 
> I suggest naming this
> 
> "has_valid_sccb_boundary", then the true/false response is clearer.
> 
>> +{
>> +    uint64_t current_len = sccb_addr + be16_to_cpu(sccb->h.length);
>> +    uint64_t allowed_len = (sccb_addr & PAGE_MASK) + PAGE_SIZE;
>> +
>> +    switch (code & SCLP_CMD_CODE_MASK) {
>> +    default:
>> +        if (current_len <= allowed_len) {
>> +            return true;
>> +        }
>> +    }
>> +    sccb->h.response_code = cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
>> +    return false;
>> +}
>> +
>> +static bool check_sufficient_sccb_len(SCCB *sccb, int size)
> 
> "has_sufficient_sccb_len" ?
> 
>> +{
>> +    MachineState *ms = MACHINE(qdev_get_machine());
>> +    int required_len = size + ms->possible_cpus->len * sizeof(CPUEntry);
> 
> Rather pass in the number of cpus instead. Looking up the machine again
> in here is ugly.

prepare_cpu_entries also looks up the machine again. Should I squeeze
in a cleanup where we pass the machine to that function too (perhaps
in the "remove SCLPDevice" patch)?

> 
>> +
>> +    if (be16_to_cpu(sccb->h.length) < required_len) {
>> +        sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
>> +        return false;
>> +    }
>> +    return true;
>> +}
>> +
>>   static void prepare_cpu_entries(CPUEntry *entry, int *count)
>>   {
>>       MachineState *ms = MACHINE(qdev_get_machine());
>> @@ -76,8 +104,7 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>>       int rnsize, rnmax;
>>       IplParameterBlock *ipib = s390_ipl_get_iplb();
>>   
>> -    if (be16_to_cpu(sccb->h.length) < (sizeof(ReadInfo) + cpu_count * sizeof(CPUEntry))) {
>> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
>> +    if (!check_sufficient_sccb_len(sccb, sizeof(ReadInfo))) {
>>           return;
>>       }
>>   
>> @@ -134,8 +161,7 @@ static void sclp_read_cpu_info(SCLPDevice *sclp, SCCB *sccb)
>>       ReadCpuInfo *cpu_info = (ReadCpuInfo *) sccb;
>>       int cpu_count;
>>   
>> -    if (be16_to_cpu(sccb->h.length) < (sizeof(ReadCpuInfo) + cpu_count * sizeof(CPUEntry))) {
>> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
>> +    if (!check_sufficient_sccb_len(sccb, sizeof(ReadCpuInfo))) {
>>           return;
>>       }
>>   
>> @@ -227,6 +253,10 @@ int sclp_service_call_protected(CPUS390XState *env, uint64_t sccb,
>>           goto out_write;
>>       }
>>   
>> +    if (!check_sccb_boundary_valid(sccb, code, &work_sccb)) {
>> +        goto out_write;
>> +    }
> 
> This is not a "factor out". You're adding new code, this needs
> justification in the patch description.

True. I'll fix up the message.

> 
>> +
>>       sclp_c->execute(sclp, &work_sccb, code);
>>   out_write:
>>       s390_cpu_pv_mem_write(env_archcpu(env), 0, &work_sccb,
>> @@ -272,8 +302,7 @@ 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)) {
>> -        work_sccb.h.response_code = cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
>> +    if (!check_sccb_boundary_valid(sccb, code, &work_sccb)) {
>>           goto out_write;
>>       }
>>   
>>
> 
> 

Renamed functions. Thanks for the review!

-- 
--
Regards,
Collin

Stay safe and stay healthy