Identifying reverse text padding infections

This is a virus infection technique that we discussed in Chapter 4, ELF Virus Technology – Linux/Unix Viruses. The idea is that a virus or parasite can make room for its code by extending the text segment in reverse. The program header for the text segment will look strange if you know what you're looking for.

Let's take a look at an ELF 64-bit binary that has been infected with a virus that uses this parasite infection method:

readelf -l ./infected_host1

Elf file type is EXEC (Executable file)
Entry point 0x3c9040
There are 9 program headers, starting at offset 225344

Program Headers:
 Type         Offset             VirtAddr           PhysAddr
              FileSiz            MemSiz              Flags  Align
 PHDR         0x0000000000037040 0x0000000000400040 0x0000000000400040
              0x00000000000001f8 0x00000000000001f8  R E    8
 INTERP       0x0000000000037238 0x0000000000400238 0x0000000000400238
              0x000000000000001c 0x000000000000001c...