Re: Unable to change the content of memory usingcrash on a live system

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Wright, David wrote:
On the other hand, there's nothing to prevent the
ambitious developer from writing their own /dev/crash driver that *does* have a write operation
in it, is there?

-- David Wright, Egenera, Inc.

Nope.  Or removing the restriction from the /dev/mem driver,
which runs into the per-arch devmem_is_allowed() function.

Here's the "arch/i386/mm/init.c" version:

/*
 * devmem_is_allowed() checks to see if /dev/mem access to a certain address is
 * valid. The argument is a physical page number.
 *
 * On x86, access has to be given to the first megabyte of ram because that area
 * contains bios code and data regions used by X and dosemu and similar apps.
 * Access has to be given to non-kernel-ram areas as well, these contain the PCI
 * mmio resources as well as potential bios/acpi data regions.
 */
int devmem_is_allowed(unsigned long pagenr)
{
        if (pagenr <= 256)
                return 1;
        if (!page_is_ram(pagenr))
                return 1;
        return 0;
}

Dave

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