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    SubjectRe: [PATCH 2/2] ramoops: remove module parameters
    From
    On Sat, Nov 19, 2011 at 1:25 AM, Marco Stornelli
    <marco.stornelli@gmail.com> 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

    --
    Kees Cook
    ChromeOS Security


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