I am currently attempting to patch a target x86
PE file from the disk with a tool, patch.exe
.
purpose
The purpose of this tool will be to eventually write/insert a multi-function payload into the target executable, who's purpose is to track the position of certain frames inside a game which I created.
background
I am doing this by mapping the file into memory with PAGE_READWRITE
protection flag. After locating the RVA of foobar(...)
function from memory, I am replacing the call to this function with a JMP (0xE9)
instruction followed by the RVA of the payload shellcode (which is previously appended to a new section I have created within the target PE file beforehand).
When the shellcode simply contains the following bytes
unsigned char shellcode[16] = {0x33, 0xc0, 0xc3, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc}
which translates to the following C function
unsigned long basic_ret() { return 0; }
the target executable successfully executes
problem
however, if I try to include another function (0xDEADBEEF
) within the code
unsigned char shellcode[32] =
{
0x6a, 0x0b, 0x68, 0x9c, 0xc2, 0xf4, 0x00, 0x6a, 0x0a, 0x68, 0xa8, 0xc2, 0xf4, 0x00, 0x68, 0xb4,
0xc2, 0xf4, 0x00, 0xb8, 0xef, 0xeb, 0xda, 0xed, 0xff, 0xd0, 0x83, 0xc4, 0x14, 0xc3, 0xcc, 0xcc
};
which translates to the following C function (a simple JMP
taking 3 arguments on the stack, to another function)
int simple_jmp()
{
typedef int (*_jmp_target)(void*, int, void*);
_jmp_target jmp_target = (_jmp_target) 0xDEADBEEF;
return jmp_target (0, 5, 0);
}
where jmp_target is filled by patch.exe
with the RVA to a function previously referred to, which was inserted into the new section of the target PE.
When the the target executable is executed, this time, it reaches some type of violation/crash (confirmed by the presence of WerFault.exe
alongside its execution).
What is the reason for this problem, what am I missing?
diagnostics
When I observe the patched bytes in memory (of the mapped PE file), I can see that 0xdeadbeef
is replaced by 0x0dc3f4de
which is the same address from which the inserted function shellcode starts. At this point, I assumed there would be no crash, little to my surprise - crash!
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