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Recognize REX-prefixed indirect JMP thunks #379

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Recognize REX-prefixed indirect JMP thunks #379

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38 changes: 27 additions & 11 deletions src/detours.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -379,6 +379,22 @@ inline PBYTE detour_gen_jmp_indirect(PBYTE pbCode, PBYTE *ppbJmpVal)
return pbCode;
}

inline BOOL detour_decode_jmp_indirect(PBYTE pbCode, PBYTE *ppbTarget)
{
ULONG cbPrefix = 0;

if ((pbCode[0] & 0xf0) == 0x40) {
cbPrefix = 1;
}

if (pbCode[cbPrefix] != 0xff || pbCode[cbPrefix + 1] != 0x25) {
return FALSE;
}

*ppbTarget = pbCode + cbPrefix + 6 + *(UNALIGNED INT32 *)&pbCode[cbPrefix + 2];
return TRUE;
}

inline PBYTE detour_gen_brk(PBYTE pbCode, PBYTE pbLimit)
{
while (pbCode < pbLimit) {
Expand All @@ -390,6 +406,7 @@ inline PBYTE detour_gen_brk(PBYTE pbCode, PBYTE pbLimit)
inline PBYTE detour_skip_jmp(PBYTE pbCode, PVOID *ppGlobals)
{
PBYTE pbCodeOriginal;
PBYTE pbTarget;

if (pbCode == NULL) {
return NULL;
Expand All @@ -399,9 +416,8 @@ inline PBYTE detour_skip_jmp(PBYTE pbCode, PVOID *ppGlobals)
}

// First, skip over the import vector if there is one.
if (pbCode[0] == 0xff && pbCode[1] == 0x25) { // jmp [+imm32]
if (detour_decode_jmp_indirect(pbCode, &pbTarget)) { // jmp [+imm32]
// Looks like an import alias jump, then get the code it points to.
PBYTE pbTarget = pbCode + 6 + *(UNALIGNED INT32 *)&pbCode[2];
if (detour_is_imported(pbCode, pbTarget)) {
PBYTE pbNew = *(UNALIGNED PBYTE *)pbTarget;
DETOUR_TRACE(("%p->%p: skipped over import table.\n", pbCode, pbNew));
Expand All @@ -417,9 +433,8 @@ inline PBYTE detour_skip_jmp(PBYTE pbCode, PVOID *ppGlobals)
pbCodeOriginal = pbCode;

// First, skip over the import vector if there is one.
if (pbCode[0] == 0xff && pbCode[1] == 0x25) { // jmp [+imm32]
if (detour_decode_jmp_indirect(pbCode, &pbTarget)) { // jmp [+imm32]
// Looks like an import alias jump, then get the code it points to.
PBYTE pbTarget = pbCode + 6 + *(UNALIGNED INT32 *)&pbCode[2];
if (detour_is_imported(pbCode, pbTarget)) {
pbNew = *(UNALIGNED PBYTE *)pbTarget;
DETOUR_TRACE(("%p->%p: skipped over import table.\n", pbCode, pbNew));
Expand Down Expand Up @@ -458,17 +473,16 @@ inline void detour_find_jmp_bounds(PBYTE pbCode,
// We have to place trampolines within +/- 2GB of code.
ULONG_PTR lo = detour_2gb_below((ULONG_PTR)pbCode);
ULONG_PTR hi = detour_2gb_above((ULONG_PTR)pbCode);
PBYTE pbJmpTarget;
DETOUR_TRACE(("[%p..%p..%p]\n", (PVOID)lo, pbCode, (PVOID)hi));

// And, within +/- 2GB of relative jmp vectors.
if (pbCode[0] == 0xff && pbCode[1] == 0x25) { // jmp [+imm32]
PBYTE pbNew = pbCode + 6 + *(UNALIGNED INT32 *)&pbCode[2];

if (pbNew < pbCode) {
hi = detour_2gb_above((ULONG_PTR)pbNew);
if (detour_decode_jmp_indirect(pbCode, &pbJmpTarget)) { // jmp [+imm32]
if (pbJmpTarget < pbCode) {
hi = detour_2gb_above((ULONG_PTR)pbJmpTarget);
}
else {
lo = detour_2gb_below((ULONG_PTR)pbNew);
lo = detour_2gb_below((ULONG_PTR)pbJmpTarget);
}
DETOUR_TRACE(("[%p..%p..%p] [+imm32]\n", (PVOID)lo, pbCode, (PVOID)hi));
}
Expand All @@ -491,6 +505,8 @@ inline void detour_find_jmp_bounds(PBYTE pbCode,

inline BOOL detour_does_code_end_function(PBYTE pbCode)
{
PBYTE pbTarget;

if (pbCode[0] == 0xeb || // jmp +imm8
pbCode[0] == 0xe9 || // jmp +imm32
pbCode[0] == 0xe0 || // jmp eax
Expand All @@ -502,7 +518,7 @@ inline BOOL detour_does_code_end_function(PBYTE pbCode)
else if (pbCode[0] == 0xf3 && pbCode[1] == 0xc3) { // rep ret
return TRUE;
}
else if (pbCode[0] == 0xff && pbCode[1] == 0x25) { // jmp [+imm32]
else if (detour_decode_jmp_indirect(pbCode, &pbTarget)) { // jmp [+imm32]
return TRUE;
}
else if ((pbCode[0] == 0x26 || // jmp es:
Expand Down