velocidex/linpmemLinux kernel driver for physical memory acquisition, enabling read access to any physical address including reserved memory and memory holes, with CR3 info and virtual-to-physical translation services.
Like its Windows counterpart, Winpmem, this is not a traditional memory dumper. Linpmem offers an API for reading from any physical address, including reserved memory and memory holes, but it can also be used for normal memory dumping. Furthermore, the driver offers a variety of access modes to read physical memory, such as byte, word, dword, qword, and buffer access mode, where buffer access mode is appropriate in most standard cases. If reading requires an aligned byte/word/dword/qword read, Linpmem will do precisely that.
Currently, the Linpmem features:
Cache Control is to be added in future for support of the specialized read access modes.
At least for now, you must compile the Linpmem driver yourself. A method to load a precompiled Linpmem driver on other Linux systems is currently under work, but not finished yet. That said, compiling the Linpmem driver is not difficult, basically it's executing 'make'.
You need make and a C compiler. (We recommend gcc, but clang should work as well).
Make sure that you have the linux-headers installed (using whatever package manager your target linux distro has). The exact package name may vary on your distribution.
A quick (distro-independent) way to check if you have the package installed:
ls -l /usr/lib/modules/`uname -r`/
That's it, you can proceed to step 2.
Foreign system: Currently, if you want to compile the driver for another system, e.g., because you want to create a memory dump but can't compile on the target, you have to download the header package directly from the package repositories of that system's Linux distribution. Double-check that the package version exactly matches the release and kernel version running on the foreign system. In case the other system is using a self-compiled kernel you have to obtain a copy of that kernel's build directory. Then, place the location of either directory in the KDIR environment variable.
export KDIR=path/to/extracted/header/package/or/kernel/root
Compiling the driver is simple, just type:
make
This should produce linpmem.ko in the current working directory.
You might want to check precompiler.h before and chose whether to compile for release or debug (e.g., with debug printing). There aren't much other precompiler settings right now.
The linpmem.ko module can be loaded by using insmod path-to-linpmem.ko, and unloaded with rmmod path-to-linpmem.ko. (This will load the driver only for this uptime.) If you compiled for debug, also take a look at dmesg.
After loading, for talking to the driver, you need to create the device:
mknod /dev/linpmem c 42 0
If you can't talk to the driver, potentially check in dmesg log to verify that '42' was indeed the registered major:
[12827.900168] linpmem: registered chrdev with major 42
Though usually the kernel would try to really assign this number.
You can use chown on the device to give it to your user, if you do not want to have a root console open all the time. (Or just keep using it in a root console.)
There is an example code demonstrating and explaining (in detail) how to interact with the driver. The user-space API reference can furthermore be found in ./userspace_interface/linpmem_shared.h.
This code is important, if you want to understand how to directly interact with the driver instead of using a library. It can also be used as a short function test.
There is an (optional) basic command line interface tool to Linpmem, the pmem CLI tool. It can be found here: https://github.com/vobst/linpmem-cli. Aside from the source code, there is also a precompiled CLI tool as well as the precompiled static library and headers that can be found here (signed). Note: this is a preliminary version, be sure to check for updates, as many additions and enhancements will follow soon.
The pmem CLI tool can be used for testing the various functions of Linpmem in a (relatively) safe and convenient manner. Linpmem can also be loaded by this tool instead of using insmod/rmmod, with some extra options in future. This also has the advantage that pmem auto-creates the right device for you for immediate use. It is extremely portable and runs on any Linux system (and, in fact, has been tested even on a Linux 2.6).
$ ./pmem -h
Command-line client for the linpmem driver
Usage: pmem [OPTIONS] [COMMAND]
Commands:
insmod Load the linpmem driver
help Print this message or the help of the given subcommand(s)
Options:
-a, --address <ADDRESS> Address for physical read operations
-v, --virt-address <VIRT_ADDRESS> Translate address in target process' address space (default: current process)
-s, --size <SIZE> Size of buffer read operations
-m, --mode <MODE> Access mode for read operations [possible values: byte, word, dword, qword, buffer]
-p, --pid <PID> Target process for cr3 info and virtual-to-physical translations
--cr3 Query cr3 value of target process (default: current process)
--verbose Display debug output
-h, --help Print help (see more with '--help')
-V, --version Print version
If you want to compile the cli tool yourself, change to its directory and follow the instructions in the (cli) Readme to build it. Otherwise, just download the prebuilt program, it should work on any Linux. To load the kernel driver with the cli tool:
# pmem insmod path/to/linpmem.ko
The advantage of using the pmem tool to load the driver is that you do not have to create the device file yourself, and it will offer (on next releases) to choose who owns the linpmem device.