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

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 10 Sep 2020 19:45:01 +0200
Thomas Huth <thuth@redhat.com> wrote:

> 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?

What about renaming it to sccb_h_len or so? That would make it more
clear that the parameter is not just some random length.

> 
>  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)) {

...name inspired by the 'h' in here.

> > +        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;
> >      }
> >   
>