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BlockAlloc: Try to allocate a block rather than returning null. #22

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BlockAlloc: Try to allocate a block rather than returning null. #22

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31 changes: 30 additions & 1 deletion mhook-lib/mhook.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -475,6 +475,7 @@ static MHOOKS_TRAMPOLINE* BlockAlloc(PBYTE pSystemFunction, PBYTE pbLower, PBYTE
ODPRINTF((L"mhooks: BlockAlloc: Looking at address %p", pbAlloc));
if (!VirtualQuery(pbAlloc, &mbi, sizeof(mbi)))
break;

// free & large enough?
if (mbi.State == MEM_FREE && mbi.RegionSize >= (unsigned)cAllocSize)
{
Expand Down Expand Up @@ -509,7 +510,35 @@ static MHOOKS_TRAMPOLINE* BlockAlloc(PBYTE pSystemFunction, PBYTE pbLower, PBYTE
ptrdiff_t bytesToOffset = (cAllocSize * (loopCount + 1) * ((loopCount % 2 == 0) ? -1 : 1));
pbAlloc = pbAlloc + bytesToOffset;
}


// Fallback: Allocate a new block at a 'random' address rather than returning null.
if (!pRetVal)
{
pRetVal = (MHOOKS_TRAMPOLINE*)VirtualAlloc(NULL, cAllocSize, MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE);
if (pRetVal)
{
size_t trampolineCount = cAllocSize / sizeof(MHOOKS_TRAMPOLINE);
ODPRINTF((L"mhooks: BlockAlloc: Fallback-allocated block at %p as %d trampolines", pRetVal, trampolineCount));

pRetVal[0].pPrevTrampoline = NULL;
pRetVal[0].pNextTrampoline = &pRetVal[1];

// prepare them by having them point down the line at the next entry.
for (size_t s = 1; s < trampolineCount; ++s)
{
pRetVal[s].pPrevTrampoline = &pRetVal[s - 1];
pRetVal[s].pNextTrampoline = &pRetVal[s + 1];
}

// last entry points to the current head of the free list
pRetVal[trampolineCount - 1].pNextTrampoline = g_pFreeList;
if (g_pFreeList)
{
g_pFreeList->pPrevTrampoline = &pRetVal[trampolineCount - 1];
}
}
}

return pRetVal;
}

Expand Down