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

[David Hildenbrand]

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 <address@hidden>
> ---
>  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.

> +
> +    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.

> +
>      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;
>      }
>  
> 


-- 
Thanks,

David / dhildenb