107 lines
3.2 KiB
Ruby
107 lines
3.2 KiB
Ruby
# This file is part of Metasm, the Ruby assembly manipulation suite
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# Copyright (C) 2007 Yoann GUILLOT
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#
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# Licence is LGPL, see LICENCE in the top-level directory
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require 'test/unit'
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require 'metasm'
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class TestMips < Test::Unit::TestCase
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def test_enc
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sc = Metasm::Shellcode.assemble(Metasm::MIPS.new(:big), <<EOS)
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;
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; MIPS nul-free xor decoder
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;
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; (C) 2006 Julien TINNES
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; <julien at cr0.org>
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;
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; The first four bytes in encoded shellcode must be the xor key
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; This means that you have to put the xor key right after
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; this xor decoder
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; This key will be considered part of the encoded shellcode
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; by this decoder and will be xored, thus becoming 4NULs, meaning nop
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;
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; This is Linux-only because I use the cacheflush system call
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;
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; You can use shellforge to assemble this, but be sure to discard all
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; the nul bytes at the end (everything after x01\\x4a\\x54\\x0c)
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;
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; change 2 bytes in the first instruction's opcode with the number of passes
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; the number of passes is the number of xor operations to apply, which should be
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; 1 (for the key) + the number of 4-bytes words you have in your shellcode
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; you must encode ~(number_of_passes + 1) (to ensure that you're nul-free)
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;.text
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;.align 2
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;.globl main
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;.ent main
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;.type main,@function
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main:
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li $14, -5 ; 4 passes
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nor $14, $14, $0 ; put number of passes in $14
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li $11,-73 ; addend to calculated PC is 73
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;.set noreorder
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next:
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bltzal $8, next
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;.set reorder
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slti $8, $0, 0x8282
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nor $11, $11, $0 ; addend in $9
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addu $25, $31, $11 ; $25 points to encoded shellcode +4
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; addu $16, $31, $11 ; $16 too (enable if you want to pass correct parameters to cacheflush
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; lui $2, 0xDDDD ; first part of the xor (old method)
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slti $23, $0, 0x8282 ; store 0 in $23 (our counter)
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; ori $17, $2, 0xDDDD ; second part of the xor (old method)
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lw $17, -4($25) ; load xor key in $17
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li $13, -5
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nor $13, $13, $0 ; 4 in $13
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addi $15, $13, -3 ; 1 in $15
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loop:
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lw $8, -4($25)
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addu $23, $23, $15 ; increment counter
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xor $3, $8, $17
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sltu $30, $23, $14 ; enough loops?
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sw $3, -4($25)
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addi $6, $13, -1 ; 3 in $6 (for cacheflush)
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bne $0, $30, loop
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addu $25, $25, $13 ; next instruction to decode :)
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; addiu $4, $16, -4 ; not checked by Linux
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; li $5,40 ; not checked by Linux
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; li $6,3 ; $6 is set above
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; .set noreorder
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li $2, 4147 ; cacheflush
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;.ascii "\\x01JT\\x0c" ; nul-free syscall
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syscall 0x52950
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; .set reorder
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; write last decoder opcode and decoded shellcode
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; li $4,1 ; stdout
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; addi $5, $16, -8
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; li $6,40 ; how much to write
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; .set noreorder
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; li $2, 4004 ; write
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; syscall
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; .set reorder
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nop ; encoded shellcoded must be here (xor key right here ;)
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; $t9 (aka $25) points here
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EOS
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assert_equal("\x24\x0e\xff\xfb\x01\xc0\x70\x27\x24\x0b\xff\xb7\x05\x10\xff\xff\x28\x08\x82\x82\x01\x60\x58\x27\x03\xeb\xc8\x21\x28\x17\x82\x82\x8f\x31\xff\xfc\x24\x0d\xff\xfb\x01\xa0\x68\x27\x21\xaf\xff\xfd\x8f\x28\xff\xfc\x02\xef\xb8\x21\x01\x11\x18\x26\x02\xee\xf0\x2b\xaf\x23\xff\xfc\x21\xa6\xff\xff\x17\xc0\xff\xf9\x03\x2d\xc8\x21\x24\x02\x10\x33\x01\x4a\x54\x0c\0\0\0\0", sc.encoded.data)
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assert_equal(28, Metasm::Shellcode.disassemble(Metasm::MIPS.new(:big), sc.encoded.data).to_s.grep(/\S/).length)
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end
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end
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