Re: problem mapping physical address from /dev/mem

[rohan puri <rohan.puri15@xxxxxxxxx>]

On Fri, Oct 7, 2011 at 3:29 PM, rohan puri <rohan.puri15@xxxxxxxxx> wrote:

On Fri, Oct 7, 2011 at 12:41 PM, Vaibhav Jain <vjoss197@xxxxxxxxx> wrote:

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

On Fri, Oct 7, 2011 at 4:13 AM, Vaibhav Jain <vjoss197@xxxxxxxxx> wrote:

On Thu, Oct 6, 2011 at 11:28 AM, Mulyadi Santosa <mulyadi.santosa@xxxxxxxxx> wrote:

Hi...

On Thu, Oct 6, 2011 at 02:34, Vaibhav Jain <vjoss197@xxxxxxxxx> 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

Another way to get the memory map is install crash module on your system and access the memory by accessing the new device /dev/crash instead of /dev/mem

Regards,
Rohan Puri
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