problem mapping physical address from /dev/mem

[Vaibhav Jain]

On Thu, Oct 6, 2011 at 9:42 PM, rohan puri <rohan.puri15 at gmail.com> wrote:

>
>
> On Fri, Oct 7, 2011 at 4:13 AM, Vaibhav Jain <vjoss197 at gmail.com> wrote:
>
>>
>>
>> On Thu, Oct 6, 2011 at 11:28 AM, Mulyadi Santosa <
>> mulyadi.santosa at gmail.com> wrote:
>>
>>> Hi...
>>>
>>> On Thu, Oct 6, 2011 at 02:34, Vaibhav Jain <vjoss197 at gmail.com> wrote:
>>> > Hi,
>>> >
>>> > I am trying to run a program that scans memory from a given physical
>>> address
>>> > using /dev/mem.
>>> > It uses mmap to map physical address from /dev/mem. So to start with I
>>> used
>>> > /proc/iomem to look up the
>>> > physical memory mapping and found the address 00010000 to be the
>>> starting
>>> > address for System ram. But whenever I
>>> > provide this address to the program it throws an error of "Operation
>>> not
>>> > permitted".
>>>
>>> Probably this could also due to mmap NULL dereferencing protection (at
>>> least that's how I name it :) )
>>>
>>> By default, the lowest 65536 byte (10000 in hex) is protected from
>>> mapping etc. It practically render such null dererefencing useless.
>>>
>>>
>>> --
>>> regards,
>>>
>>> Mulyadi Santosa
>>> Freelance Linux trainer and consultant
>>>
>>> blog: the-hydra.blogspot.com
>>> training: mulyaditraining.blogspot.com
>>>
>>
>> Hi,
>>
>> I tried the same with other addresses (greater than 0x10000 ) also but it
>> is throwing the same error.
>> Is there a way to get over this ?
>>
>> Thanks
>> Vaibhav Jain
>>
>>
>>
>> _______________________________________________
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>>
>> Hi Vaibhav,
>
> This is how it can be done. Refer link
> http://www.theknotter.net/system-memory-dumps-on-linux/
>
> I have attached the modified code which disables the socket creation part
> and dumps the output in a file.
>
> Regards,
> Rohan Puri
>


Thanks Rohan for the code but I already have a code that reads memory using
/dev/mem and mmap.
Only difference is I have to manually change the starting address in
program. The problem is whenver I give
any System RAM address the mmap call fails with 'Operation not permitted'. I
googled a little and found that normally
this operation is not allowed and the kernel has to be compiled with
CONFIG_STRICT_DEVMEM disabled to read any memory
location in this way. I also found out about the boot option 'strict-devmem
=0'. I tried both these options but none of them seems to working.
So I am trying to figure out if there is some other setting that I need to
change.
I am doing this on Fedora 15 - 2.6.38 kernel.

Thanks
Vaibhav Jain
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