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show what happens when mhook hooks loop

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2018-01-09 19:18:59 +01:00
parent eaf5645f37
commit d7be996331
1 changed files with 45 additions and 41 deletions
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@@ -95,29 +95,14 @@ instruction lengths & offsets.
0026 | 48 83 E0 01 | and rax,1
002A | 74 17 | je test_cases.0043 ----+
002C | 48 31 C0 | xor rax,rax |
002F | 90 | nop |
0030 | 90 | nop |
0031 | 90 | nop |
0032 | 90 | nop |
0033 | 90 | nop |
0034 | 90 | nop |
0035 | 90 | nop |
0036 | 90 | nop |
0037 | 90 | nop |
0038 | 90 | nop |
0039 | 90 | nop |
003A | 90 | nop |
003B | 90 | nop |
003C | 90 | nop |
003D | 90 | nop |
003E | 90 | nop |
003F | 90 | nop |
0040 | 90 | nop |
0041 | 90 | nop |
0042 | 90 | nop |
0043 | C3 | ret <-----------------+
002A | 74 17 | je test_cases.0043 --+
002C | 48 31 C0 | xor rax,rax |
002F | 90 | nop |
0030 | 90 | nop |
... |
0041 | 90 | nop |
0042 | 90 | nop |
0043 | C3 | ret <----------------+
This function has a branch in the first 5 bytes. Hooking it detour-style isn't
@@ -198,27 +183,46 @@ instructions that have been overwritten. Consider this:
There's only 3 bytes that can be safely overwritten. Right after that is the
destination of the jump backwards. This is a very simple (and kinda pointless)
function so detecting that the loop might lead to problems shouldn't be a
problem. Basically the same applies for the next example:
problem. But consider what happens with MHook (and all the others):
public _tail_recursion
_tail_recursion:
test ecx, ecx
je @is_0
mov eax, ecx
dec ecx
@loop:
test ecx, ecx
jz @tr_end
_loop original:
mul ecx
dec ecx
008C | 48 89 C8 | mov rax,rcx
008F | 48 F7 E1 | mul rcx
0092 | 90 | nop
0093 | 90 | nop
0094 | 90 | nop
0095 | E2 F8 | loop test_cases.008F
0097 | C3 | ret
jnz @loop
jmp @tr_end
@is_0:
mov eax, 1
@tr_end:
ret
_loop hooked:
008C | E9 0F 69 23 00 | jmp <MHook_Hooks::hookLoop>
0091 | E1 90 | loope test_cases.0023
0093 | 90 | nop
0094 | 90 | nop
0095 | E2 F8 | loop test_cases.008F
0097 | C3 | ret
trampoline:
00007FFF7CD200C0 | 48 89 C8 | mov rax,rcx
00007FFF7CD200C3 | 48 F7 E1 | mul rcx
00007FFF7CD200C6 | E9 C7 96 DC FF | jmp test_cases.0092
then executes:
0092 | 90 | nop
0093 | 90 | nop
0094 | 90 | nop
0095 | E2 F8 | loop test_cases.008F
But that jumps back into the middle of the jump and thus executes:
008F | 23 00 | and eax,dword ptr ds:[rax]
0091 | E1 90 | loope test_cases.0023
Which isn't right and will crash horribly.
(Preliminary) Results
=====================