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What is CrashOS?

CrashOS is a tool dedicated to the research of vulnerabilities in hypervisors by creating unusual system configurations. CrashOS is a minimalist Operating System which aims to lead to hypervisor crashs, hence its name. You can launch existing tests or implement your owns and observe hypervisor behaviour towards this unusual kernel.

The core of CrashOS provides the following OS features:

  • the Boot entry;
  • the memory management (segmentation and paging);
  • the interrupt and exception handling;
  • the I/O communication.

A default kernel configuration is available but this set of features allows to entirely reconfigure the kernel as you desire.

Note : CrashOS is a work in progress. Please report any issue here.

Hardware and software requirements

CrashOS only works on Intel x86 hardware architecture, requires gcc-multilib (to be compiled under x86-64) and GRUB to boot. The kernel is multiboot compliant.

Installation (ie. VMWare)

To install CrashOS, first compile the project with the main Makefile. It will create the 32-bits executable test.bin. .../crashos$ make

Then install test.bin on the provided VMWare disk image to test it under VMWare hypervisor. You need vmware-mountcommand line tool and the ability to mount ext2 filesystems.

.../crashos$ sudo make install

Usage

Use the script create_new_test_directory.py to create a new directory containing your test. It will create the local Makefile, a log file to store the test logs, a text file to describe the test and the test file filled with the test template.

/crashos/tools$ python create_new_test_directory.py myowntest
Directory myowntest created
/crashos/tools$ cd ..
/crashos$ ls src/myowntest/
Makefile  myowntest.c  myowntest.log  myowntest.txt

In CrashOS, each test needs to define a specific kernel configuration. Thus, each test must contain:

  • an "init" function: it saves the current kernel configuration and defines the configuration with which we want to work;
  • the "test" function;
  • a "restore" function: it recovers the old kernel configuration.

A test template is available here.

To init the kernel, some default functions are available (init.h and init.c):

Function Description
init_work_mem() Initialize the mem_info struct to define the available physical memory
init_segmentation(...) Initialize the GDT (Global Descriptor Table) with the following entries and update gdtr and segment selectors
init_paging(...) Initialize the PGD with the first 4MB in Identity Mapping, update CR3 and CR4 and enable the paging in CR0
init_interrupts(...) Initialize the IDT (Interrupt Descriptor Table) with the following entries (32 first entries for exceptions)

Others functions allow the developer to modify the default system parameters and to define his own configuration. The following command line generates a a code documentation for all functions available in CrashOS: .../crashos$ make doc It will create a html documentation in doxygen_documentation/html/index.html.

Specify, in the main Makefile, the list of tests you want to launch:

...
TESTS :=  test_repo1 test_repo2 
...

Then, rebuild the project. .../crashos$ make

License

CrashOS is released under GPLv2.

References

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