Hi Edwin,

This is the effect of swapping. When you dump a vma region to disk, we zero-pad pages that are swapped to retain the original size and offsets in the vma region. You can call proc_as.is_valid_address(0x7faf9d9b0e9b) and if its False then the page containing that address is in the pagefile. You can also use proc_as.zread() instead of read() which will automatically zero-pad pages that are not memory resident.

MHL

On Wed, Jun 19, 2013 at 9:15 AM, Edwin Smulders <edwin.smulders@gmail.com> wrote:

Hi all,

I am having a problem reading certain values in an address space. I
know for certain that the range I am trying to read is mapped, i.e.
there is a vma for it.

The specific range in this case is shown in the vma list as this:

1206 0x00007faf9d98f000 0x00007faf9db4d000 r-x 0x0
8 1 241 /lib/x86_64-linux-gnu/libc-2.17.so

The offset in this range that I am trying to read is 0x21e9b = 0x7faf9d9b0e9b

the call may look like this: proc_as.read(0x7faf9d9b0e9b, 10)
and it will return None, meaning it could not read that address.

Using the linux_dump_map I exported the whole range and there's a
pretty big empty (inaccessible) chunk in the middle, which appears as
0-bytes in the export. I know for a fact that my libc does not have a
big area of 0-bytes, so this is pretty weird. It also works just fine
for other processes in the same dump (so using the same libc).

For research purposes I make my memory dumps with virtualbox, so I
don't think it's an issue with memory corruption; as far as i can
tell, virtualbox makes complete snapshots.

Does anyone know what might cause this problem?

Cheers,
Edwin
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