root cannot write to Linux RAM Post: 302583965

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Special Forums Cybersecurity root cannot write to Linux RAM Post 302583965 by Alux on Wednesday 21st of December 2011 10:08:15 PM

12-21-2011

Registered User

OK, I want my code above to work with Linux. I'm an out of work systems hacker and this seems like a fun way of passing the time.

Some questions;

1.Do Linux Device Drivers operate at Ring 0?

2. Would the ability to read and update Kernel memory require writing a device driver or changing the Memory Management of Linux?

My main concern is the 'freeing' of the Linux kernel. So that the safety comes off, and the ability to make live updates without server downtime are possible.

Plus, such a feature would be fun! *smiles*

Corona, you hinted at a /dev/kmem file. I'm new to Linux systems programming, but have a couple of books on writing device drivers for Linux.

My ideas at this point are double;

1. /dev/kmem returns a raw dump of memory without formatting

2. /dev/kmem returns a formatted hexidecimal / Intel ASM output of the RAM in columns sided with RAM Addresses

My paths are thus;

1. Access the Global descriptor table task state segment of the kernel to obtain RAM values for access at a later point in the device driver. (Is that possible?)

2. Access the Process Table in Linux for a list of processes and start/stop address blocks. (Unsafe?)

So many questions at this point in time, not sure where to go for guidance on Linux systems programming.

Oh, if anyone when reading this post suddenly has a website link they think would be useful, or a book to purchase to help, any resources actually, I'd be happy to read up on the subject to make this idea possible.

Basically, what I want is to do the following in C;

Code:

void main() {

fd = open("/dev/kmem", 'rw');

// fd opens to beginning of kernel space in RAM

poke_ram(fd, $var);

seek(fd);

read(fd, buf...);

process(fd);

close(fd);

}
}

Rather simple idea? But how to make this code work with Linux?

Thank you for taking the time to read about my new idea.

I'm currently working on my own OS. It runs only in ring 0, and has full access to the RAM and kernel code. Never enters ring 4. Have you heard about self-modifying code? That is a passion of mine. The OS currently only is in text mode, protected mode with segmentation, and has a blue sky with white stars signifying the beginning of the end.

Last edited by Alux; 12-22-2011 at 02:18 AM..

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LEARN ABOUT MINIX

port

MEM(4)                                                       Linux Programmer's Manual                                                      MEM(4)

NAME

       mem, kmem, port - system memory, kernel memory and system ports

DESCRIPTION

       /dev/mem is a character device file that is an image of the main memory of the computer.  It may be used, for example, to examine (and even
       patch) the system.

       Byte addresses in /dev/mem are interpreted as physical memory addresses.  References to nonexistent locations cause errors to be returned.

       Examining and patching is likely to lead to unexpected results when read-only or write-only bits are present.

       Since Linux 2.6.26, and depending on the architecture, the CONFIG_STRICT_DEVMEM kernel configuration option limits the areas which  can  be
       accessed through this file.  For example: on x86, RAM access is not allowed but accessing memory-mapped PCI regions is.

       It is typically created by:

           mknod -m 660 /dev/mem c 1 1
           chown root:kmem /dev/mem

       The  file  /dev/kmem  is  the same as /dev/mem, except that the kernel virtual memory rather than physical memory is accessed.  Since Linux
       2.6.26, this file is available only if the CONFIG_DEVKMEM kernel configuration option is enabled.

       It is typically created by:

           mknod -m 640 /dev/kmem c 1 2
           chown root:kmem /dev/kmem

       /dev/port is similar to /dev/mem, but the I/O ports are accessed.

       It is typically created by:

           mknod -m 660 /dev/port c 1 4
           chown root:kmem /dev/port

FILES

       /dev/mem
       /dev/kmem
       /dev/port

SEE ALSO

       chown(1), mknod(1), ioperm(2)

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux                                                               2015-01-02                                                              MEM(4)

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