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/*
* Copyright © 2021 Michael Smith <mikesmiffy128@gmail.com>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
* OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
* PERFORMANCE OF THIS SOFTWARE.
*/
#include <string.h>
#include "con_.h"
#include "intdefs.h"
#include "mem.h"
#include "os.h"
#include "udis86.h"
// Warning: half-arsed hacky implementation (because that's all we really need)
// Almost certainly breaks in some weird cases. Oh well! Most of the time,
// vtable hooking is more reliable, this is only for, uh, emergencies.
#if defined(_WIN32) && !defined(_WIN64)
__attribute__((aligned(4096)))
static uchar trampolines[4096];
static uchar *nexttrampoline = trampolines;
__attribute__((constructor))
static void setrwx(void) {
// PE doesn't support rwx sections, not sure about ELF. Eh, just hack it in
// a constructor instead. If this fails and we segfault later, too bad!
os_mprot(trampolines, sizeof(trampolines), PAGE_EXECUTE_READWRITE);
}
#define RELJMP 0xE9 // the first byte of a 5-byte jmp
void *hook_inline(void *func_, void *target) {
uchar *func = func_;
if (!os_mprot(func, 5, PAGE_EXECUTE_READWRITE)) return false;
struct ud udis;
ud_init(&udis);
ud_set_mode(&udis, 32);
// max insn length is 15, we overwrite 5, so max to copy is 4 + 15 = 19
ud_set_input_buffer(&udis, func, 19);
int len = 0;
while (ud_disassemble(&udis) && len < 5) {
if (ud_insn_mnemonic(&udis) == UD_Ijmp ||
ud_insn_mnemonic(&udis) == UD_Icall) {
con_warn("hook_inline: jmp adjustment NYI\n");
return 0;
}
len += ud_insn_len(&udis);
}
// for simplicity, just bump alloc the trampoline. no need to free anyway
if (nexttrampoline - trampolines > len + 6) goto nospc;
uchar *trampoline = (uchar *)InterlockedExchangeAdd(
(volatile long *)&nexttrampoline, len + 6);
if (trampoline - trampolines > len + 6) { // avoid TOCTOU
nospc: con_warn("hook_inline: out of trampoline space\n");
return 0;
}
*trampoline++ = len; // stick length in front for quicker unhooking
memcpy(trampoline, func, len);
trampoline[len] = RELJMP;
uint diff = func - (trampoline + 5); // goto the continuation
memcpy(trampoline + len + 1, &diff, 4);
uchar jmp[8];
jmp[0] = RELJMP;
diff = (uchar *)target - (func + 5); // goto the hook target
memcpy(jmp + 1, &diff, 4);
// pad with original bytes so we can do an 8-byte atomic write
memcpy(jmp + 5, func + 5, 3);
*(volatile uvlong *)func = *(uvlong *)jmp; // (assuming function is aligned)
FlushInstructionCache(GetCurrentProcess(), func, len);
return trampoline;
}
void unhook_inline(void *orig) {
uchar *p = (uchar *)orig;
int len = p[-1];
uint off = mem_load32(p + len + 1);
uchar *q = p + off + 5;
memcpy(q, p, 5); // XXX not atomic atm! (does any of it even need to be?)
FlushInstructionCache(GetCurrentProcess(), q, 5);
}
#else
// TODO(linux): Implement for Linux and/or x86_64 when needed...
#endif
// vi: sw=4 ts=4 noet tw=80 cc=80
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