rekcap:packer
Packing:
* Create elf header
* Add single program header which will load whole binary into memory
* Shove in some compiled position independent assembly and set p_entry
* Provide random elf and XOR it into RW segment
* Correctly set offsets and sizes (must be 0x200000 between PT_LOAD segments)
Unpacking:
* Traverse stack to AUXV
* Extract elf program header info from AUXV
* mmap(exec|write) to elf scratch pad
* XOR original elf from segment into newly mapped memory
* Foreach PT_LOAD segment in original elf : mmap and memcpy
* Get PT_INTERP segment in original elf, path to ld-linux
* fstat, mmap and read in ld-linux
* Foreach PT_LOAD segment in ld-linux : mmap and memcpy (DYN so .text is va:0, needs random address)
* Update the auxv with values from original elf
* Update AT_BASE in auxv with address ld-linux .text segment loaded to
* Jump to ld-linux e_entry
Auxillary Vector Keys:
AT_PHDR : 3
AT_PHENT : 4
AT_PHNUM : 5
AT_ENTRY : 9
Userland Exec Paper:
https://grugq.github.io/docs/ul_exec.txt