Re: [PATCH v5 2/8] s390/sclp: rework sclp boundary checks

[Thomas Huth]

On 10/09/2020 11.36, Collin Walling wrote:
> Rework the SCLP boundary check to account for different SCLP commands
> (eventually) allowing different boundary sizes.
> 
> Signed-off-by: Collin Walling <walling@linux.ibm.com>
> Acked-by: Janosch Frank <frankja@linux.ibm.com>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> ---
>  hw/s390x/sclp.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
> index 28b973de8f..69a8724dc7 100644
> --- a/hw/s390x/sclp.c
> +++ b/hw/s390x/sclp.c
> @@ -49,6 +49,18 @@ static inline bool sclp_command_code_valid(uint32_t code)
>      return false;
>  }
>  
> +static bool sccb_verify_boundary(uint64_t sccb_addr, uint16_t len)

Maybe it would be good to add a comment in front of the function to say
that len must be big endian?

 Thomas

> +{
> +    uint64_t sccb_max_addr = sccb_addr + be16_to_cpu(len) - 1;
> +    uint64_t sccb_boundary = (sccb_addr & PAGE_MASK) + PAGE_SIZE;
> +
> +    if (sccb_max_addr < sccb_boundary) {
> +        return true;
> +    }
> +
> +    return false;
> +}
> +
>  static void prepare_cpu_entries(MachineState *ms, CPUEntry *entry, int 
> *count)
>  {
>      uint8_t features[SCCB_CPU_FEATURE_LEN] = { 0 };
> @@ -229,6 +241,11 @@ int sclp_service_call_protected(CPUS390XState *env, 
> uint64_t sccb,
>          goto out_write;
>      }
>  
> +    if (!sccb_verify_boundary(sccb, work_sccb.h.length)) {
> +        work_sccb.h.response_code = 
> cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
> +        goto out_write;
> +    }
> +
>      sclp_c->execute(sclp, &work_sccb, code);
>  out_write:
>      s390_cpu_pv_mem_write(env_archcpu(env), 0, &work_sccb,
> @@ -274,7 +291,7 @@ 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)) {
> +    if (!sccb_verify_boundary(sccb, work_sccb.h.length)) {
>          work_sccb.h.response_code = 
> cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
>          goto out_write;
>      }
>