problem mapping physical address from /dev/mem

[rohan puri]

On Fri, Oct 7, 2011 at 12:41 PM, Vaibhav Jain <vjoss197 at gmail.com> wrote:

> 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
>
>
Hi Vaibhav,

My iomem file : -

00000000-0000ffff : reserved
*00010000-0009f3ff : System RAM*
0009f400-0009ffff : reserved
000c0000-000c7fff : Video ROM
000cc000-000ccfff : Adapter ROM
000cd000-000cffff : pnp 00:0c
000e0000-000effff : pnp 00:0c
000f0000-000fffff : reserved
  000f0000-000fffff : System ROM
*00100000-cf6dffff : System RAM*
  01000000-015dadf2 : Kernel code
  015dadf3-01ab907f : Kernel data
  01bb1000-01d04fff : Kernel bss

Now the program which i sent you, with that I am able to read the 1st part
of System RAM successfully. I am getting the operation not permitted error
from mmap  for second part of System RAM. Can you verify the same on your
system. I mean are you able to read the 1st part (if your System RAM is
divided) or not ?

Regards,
Rohan Puri
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