Re: [PATCH 2/2] ramoops: remove module parameters

[Marco Stornelli]

Il 21/11/2011 19:11, Kees Cook ha scritto:
> On Sat, Nov 19, 2011 at 1:25 AM, Marco Stornelli
> <marco.stornelli@xxxxxxxxx>  wrote:
> > Il 18/11/2011 20:31, Kees Cook ha scritto:
> > > The ramoops driver is intended to be used with platforms that define
> > > persistent memory regions. If memory regions were configurable with
> > > module parameters, it would be possible to read some RAM regions via
> > > the pstore interface without access to /dev/mem (which would result
> > > in a loss of kernel memory privacy when a system is built with
> > > STRICT_DEVMEM), so remove this ability completely.
> >
> > I don't like it very much. The loss of module parameters give us less
> > flexibility. The main goal of this driver is debug, so I think it should be
> > fast to use. I mean it's not more possible reserve a memory region and load
> > the module "on-the-fly", it needs a platform device, it's ok but I think
> > it's a little bit more complicated, (without talking about platforms without
> > a device tree source).
> > I don't understand the problem of strict devmem. We shouldn't use kernel
> > memory region but only reserved ones and the driver doesn't use the
> > request_mem_region_exclusive, am I wrong?
>
> Hmmm, maybe I'm reading it backwards, but I think we want it to use
> ..._exclusive().
>
> int devmem_is_allowed(unsigned long pagenr)
> {
>          if (pagenr<= 256)
>                  return 1;
>          if (iomem_is_exclusive(pagenr<<  PAGE_SHIFT))
>                  return 0;
>          if (!page_is_ram(pagenr))
>                  return 1;
>          return 0;
> }
>
> If the region is exclusive, access is not allowed (return 0). ramoops
> currently uses request_mem_region() instead of
> request_mem_region_exclusive(). If we made that switch, I think I'd be
> happy. Would this create some problem I'm not seeing?
>
> -Kees

I don't understand why we should use the exclusive version, to protect 
debug data? You should provide a more valid reason to change, because 
the fact you will be happier with this change is not enough for me :)

Marco
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/