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USAGE.md

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Plugin: osi_linux

Summary

osi_linux provides Linux introspection information and makes it available through the OSI interface. It does so by knowing about the offsets for various Linux kernel data structures and then providing algorithms that traverse these data structures in the guest virtual machine.

Because the offsets of fields in Linux kernel data structures change frequently (and can even depend on the specific compilation flags used), osi_linux uses a configuration file to specify the offsets of critical data structures. An portion of such a configuration file, which is in the GLib key-value format (similar to .ini files), is given below:

[debian-3.2.63-i686]
name = #1 Debian 3.2.63-2+deb7u1 i686
task.size = 1000
#task.init_addr = 0xC1397480
task.init_addr = 3241768064
task.task_offset = 0
task.tasks_offset = 204
task.pid_offset = 248

[... omitted ...]

[debian_wheezy_i386_desktop] 
name = #1 SMP Debian 3.2.51-1 i686
task.size = 1060
#task.init_addr = 0xC13E0FE0
task.init_addr = 3242069984
task.task_offset = 0
task.tasks_offset = 212
task.pid_offset = 292
task.tgid_offset = 296
task.group_leader_offset = 328

[... omitted ...]

Of course, generating this file by hand would be extremely painful. So instead we can generate it automatically by building and loading a kernel module in the guest OS.

To do so, you will need the kernel headers and a compiler installed in the guest. On a Debian guest, you can do:

# apt-get install build-essential linux-headers-`uname -r`

Then copy the panda_plugins/osi_linux/utils/kernelinfo directory into the guest (e.g., using scp from inside the guest or simply by cloning the PANDA repository), and run make to build kernelinfo.ko. Finally, insert the kernel module and run dmesg to get the values. Note that although insmod will return an "Operation not permitted" error, it will still print the right information to the log:

# insmod kernelinfo.ko
Error: could not insert module kernelinfo.ko: Operation not permitted
# dmesg

You should see output in the dmesg log like:

[166368.803659] --KERNELINFO-BEGIN--
[166368.804324] name = #1 SMP Debian 3.2.51-1 i686
[166368.804390] task.size = 1060
[166368.804509] #task.init_addr = 0xC13E0FE0
[166368.804530] task.init_addr = 3242069984
[166368.804594] task.task_offset = 0
[166368.804639] task.tasks_offset = 212
[166368.804685] task.pid_offset = 292
[166368.804719] task.tgid_offset = 296
[166368.804748] task.group_leader_offset = 328
[166368.804781] task.thread_group_offset = 384
[166368.804808] task.real_parent_offset = 304
[166368.804836] task.parent_offset = 308
[166368.804861] task.mm_offset = 240
[166368.804885] task.stack_offset = 4
[166368.804912] task.real_cred_offset = 504
[166368.804936] task.cred_offset = 508
[166368.804966] task.comm_offset = 516
[...]
[166368.805736] fs.d_iname_offset = 36
[166368.805761] fs.d_parent_offset = 16
[166368.805778] ---KERNELINFO-END---

Copy this information (without the KERNELINFO-BEGIN and KERNELINFO-END lines) into the kernelinfo.conf. Be sure to put it in its own configuration section, i.e.:

[my_kernel_info]
name = #1 SMP Debian 3.2.51-1 i686
task.size = 1060
[...]

The name you give (my_kernel_info in this case) should then be passed as the kconf_group argument to the plugin.

Arguments

  • kconf_file: string, defaults to "kernelinfo.conf". The location of the configuration file that gives the required offsets for different versions of Linux.
  • kconf_group: string, defaults to "debian-3.2.65-i686". The specific configuration desired from the kernelinfo file (multiple configurations can be stored in a single kernelinfo.conf).

Dependencies

osi_linux is an introspection provider for the osi plugin.

APIs and Callbacks

In addition to providing the standard APIs used by OSI, osi_linux also provides two Linux-specific API calls that resolve file descriptors to filenames and tell you the current file position:

// returns fd for a filename or a NULL if failed
char *osi_linux_fd_to_filename(CPUState *env, OsiProc *p, int fd);

// returns pos in a file 
unsigned long long  osi_linux_fd_to_pos(CPUState *env, OsiProc *p, int fd);

Example

Assuming you have a kernelinfo.conf in the current directory with a configuration named my_kernel_info, you can run the OSI test plugin on a Linux replay as follows:

$PANDA_PATH/x86_64-softmmu/qemu-system-x86_64 -replay foo \
    -panda osi -panda osi_linux:kconf_file=kernelinfo.conf,kconf_group=my_kernel_info \
    -panda osi_test