1. ./a.out Having fun with system internals Facundo de la Cruz (@_tty0)

2. Facundo M. de la Cruz IT Consultant on DC Solutions High Availability Expert Red Hat Enterprise Linux Certified Instructor Oracle Solaris official Instructor GPG ID: 0x5627089 I write on my blog and in my Twitter http://codigounix.blogspot.com.ar/ http://twitter.com/_tty0 About me

3. Facundo M. de la Cruz (tty0) IT Consultant on DC Solutions High Availability Expert Red Hat Enterprise Linux Certified Instructor Oracle Solaris official Instructor GPG ID: 0x5627089 I write on my blog and in my Twitter http://codigounix.blogspot.com.ar/ http://twitter.com/_tty0 About me

4. Facundo M. de la Cruz IT Consultant on DC Solutions High Availability Expert Red Hat Enterprise Linux Certified Instructor Oracle Solaris official Instructor GPG ID: 0x5627089 I write on my blog and in my Twitter http://codigounix.blogspot.com.ar/ http://twitter.com/_tty0 About me

5. Facundo M. de la Cruz IT Consultant on DC Solutions High Availability Expert Red Hat Enterprise Linux Certified Instructor Oracle Solaris official Instructor GPG ID: 0x5627089 I write on my blog and in my Twitter http://codigounix.blogspot.com.ar/ http://twitter.com/_tty0 About me

6. Facundo M. de la Cruz IT Consultant on DC Solutions High Availability Expert Red Hat Enterprise Linux Certified Instructor Oracle Solaris official Instructor GPG ID: 0x5627089 I write on my blog and in my Twitter http://codigounix.blogspot.com.ar/ http://twitter.com/_tty0 About me

7. Facundo M. de la Cruz IT Consultant on DC Solutions High Availability Expert Red Hat Enterprise Linux Certified Instructor Oracle Solaris official Instructor GPG ID: 0x5627089 I write on my blog and in my Twitter http://codigounix.blogspot.com.ar/ http://twitter.com/_tty0 About me

8. Facundo M. de la Cruz IT Consultant on DC Solutions High Availability Expert Red Hat Enterprise Linux Certified Instructor Oracle Solaris official Instructor GPG ID: 0x5627089 I write on my blog and in my Twitter http://codigounix.blogspot.com.ar/ http://twitter.com/_tty0 About me

9. Facundo M. de la Cruz IT Consultant on DC Solutions High Availability Expert Red Hat Enterprise Linux Certified Instructor Oracle Solaris official Instructor GPG ID: 0x5627089 I write on my blog and in my Twitter http://codigounix.blogspot.com.ar/ http://twitter.com/_tty0 About me

10. Facundo M. de la Cruz IT Consultant on DC Solutions High Availability Expert Red Hat Enterprise Linux Certified Instructor Oracle Solaris official Instructor GPG ID: 0x5627089 I write on my blog and in my Twitter http://codigounix.blogspot.com.ar/ http://twitter.com/_tty0 About me

11. Facundo M. de la Cruz IT Consultant on DC Solutions High Availability Expert Red Hat Enterprise Linux Certified Instructor Oracle Solaris official Instructor GPG ID: 0x5627089 I write on my blog and in my Twitter http://codigounix.blogspot.com.ar/ http://twitter.com/_tty0 About me

12. ➔ Real mode - 20 bits segmented memory address space. - Only 1 MB of memory can be addressed. - Direct access to BIOS (EFI/UEFI ???) ➔ Protected mode - Provide protected memory. - Memory paging support. - Global Descriptor Table (GDT) and Local Descriptor Table (LDT). ➔ Long mode - 64 bits address: 16 EB of memory address (16 billion of GB) - 64 bits instructions and registers. - 16 and 32 bits programs are executed in a sub mode. - Extension of the 32-bit instruction set, but unlike the 16–to–32-bit transition CPU operation modes

13. There are four privilege levels, numbered 0 (most privileged) to 3 (least privileged), and three main resources being protected: memory, I/O ports, and the ability to execute certain machine instructions. About 15 machine instructions, out of dozens, are restricted by the CPU to ring zero. CPU privilege separation

14. System calls

15. o An exit program in ANSI C o The same program in INTEL x86 ASM System calls

17. From arch/x86/include/asm/unistd_32.h

18. System calls From arch/x86/include/asm/unistd_32.h From exit(3) man page

19. Having fun with ELF

21. From../include/linux/elf.h

22. Having fun with ELF

23. From../include/linux/elf.h

24. Having fun with ELF From../include/linux/elf.h

25. Having fun with ELF

29. ELF Sections and Segments.bss Uninitialized data ( static int i; ).data Initialized data (static, global, and local variables).rodata Static constants and strings..text Program instructions (code)

30. ELF Sections and Segments.bss Uninitialized data ( static int i; ).data Initialized data (static, global, and local variables).rodata Static constants and strings..text Program instructions (code)

31. ELF Sections and Segments

34. Shellcode looks like…

35. Questions??? }:-)

36. And finishing… Thanks…