This function allocate a space near of a memory block that could be used by a trampoline function in hooking libraries.

allocator.cpp

#include <Windows.h>

#define MAX_MEMORY_RANGE 0x40000000
#define IS_POINTER_BETWEEN(P, MAX, MIN) (((ULONG_PTR)P < (ULONG_PTR)MAX) && ((ULONG_PTR)P > (ULONG_PTR)MIN))

#define PAGE_EXECUTE_FLAGS \
    PAGE_EXECUTE | \
    PAGE_EXECUTE_READ | \
    PAGE_EXECUTE_READWRITE | \
    PAGE_EXECUTE_WRITECOPY

PVOID WINAPI VirtualAllocNearLowerPage(
    IN HANDLE ProcessHandle,
    IN PVOID Address,
    IN PVOID MinAddress,
    IN PVOID MaxAddress,
    IN SIZE_T AllocationSize,
    IN DWORD AllocationType,
    IN DWORD AllocationProtection,
    IN DWORD AllocationGranularity)
{
    MEMORY_BASIC_INFORMATION MemoryInfo = { 0 };
    ULONG_PTR BaseAddress = (ULONG_PTR)Address;
    BaseAddress -= BaseAddress % AllocationGranularity;
    BaseAddress -= AllocationGranularity;

    while (VirtualQueryEx(ProcessHandle, (LPVOID)BaseAddress, &MemoryInfo, sizeof(MemoryInfo)) == sizeof(MemoryInfo))
    {
        if (!IS_POINTER_BETWEEN(BaseAddress, MaxAddress, MinAddress)) {
            break;
        }

        if (!IS_POINTER_BETWEEN(BaseAddress, MaxAddress, AllocationGranularity)) {
            break;
        }

        if (MemoryInfo.State == MEM_FREE) {
            return VirtualAllocEx(
                ProcessHandle,
                (LPVOID)BaseAddress,
                AllocationSize,
                AllocationType,
                AllocationProtection);
        }

        BaseAddress = (ULONG_PTR)MemoryInfo.BaseAddress - AllocationGranularity;
    }

    return NULL;
}

PVOID WINAPI VirtualAllocNearUpperPage(
    IN HANDLE ProcessHandle,
    IN PVOID Address,
    IN PVOID MinAddress,
    IN PVOID MaxAddress,
    IN SIZE_T AllocationSize,
    IN DWORD AllocationType,
    IN DWORD AllocationProtection,
    IN DWORD AllocationGranularity)
{
    MEMORY_BASIC_INFORMATION MemoryInfo = { 0 };
    ULONG_PTR BaseAddress = (ULONG_PTR)Address;
    BaseAddress -= BaseAddress % AllocationGranularity;
    BaseAddress += AllocationGranularity;

    while (VirtualQueryEx(ProcessHandle, (LPVOID)BaseAddress, &MemoryInfo, sizeof(MemoryInfo)) == sizeof(MemoryInfo))
    {
        if (!IS_POINTER_BETWEEN(BaseAddress, MaxAddress, MinAddress)) {
            break;
        }

        if (MemoryInfo.State == MEM_FREE) {
            return VirtualAllocEx(
                ProcessHandle,
                (LPVOID)BaseAddress,
                AllocationSize,
                AllocationType,
                AllocationProtection);
        }

        BaseAddress = (ULONG_PTR)MemoryInfo.BaseAddress + MemoryInfo.RegionSize;
        BaseAddress += static_cast<ULONG_PTR>(AllocationGranularity) - 1;
        BaseAddress -= BaseAddress % AllocationGranularity;
    }

    return NULL;
}

PVOID WINAPI VirtualAllocNearPage(
    IN HANDLE ProcessHandle,
    IN PVOID Address,
    IN PVOID MinAddress,
    IN PVOID MaxAddress,
    IN SIZE_T AllocationSize,
    IN DWORD AllocationType,
    IN DWORD AllocationProtection,
    IN DWORD AllocationGranularity)
{
    PVOID NearLowerPageAddress = VirtualAllocNearLowerPage(
        ProcessHandle,
        Address,
        MinAddress,
        MaxAddress,
        AllocationSize,
        AllocationType,
        AllocationProtection,
        AllocationGranularity);

    if (NearLowerPageAddress) {
        return NearLowerPageAddress;
    }

    PVOID NearUpperPageAddress = VirtualAllocNearUpperPage(
        ProcessHandle,
        Address,
        MinAddress,
        MaxAddress,
        AllocationSize,
        AllocationType,
        AllocationProtection,
        AllocationGranularity);

    return NearUpperPageAddress;
}

PVOID WINAPI AllocateBlockNearPage(
    IN HANDLE ProcessHandle,
    IN PVOID Address,
    IN DWORD AllocationType,
    IN DWORD AllocationProtection)
{
    SYSTEM_INFO SystemInfo = { 0 };
    GetSystemInfo(&SystemInfo);

    ULONG_PTR BaseAddress = (ULONG_PTR)Address;
    ULONG_PTR MinAddress = (ULONG_PTR)SystemInfo.lpMinimumApplicationAddress;
    ULONG_PTR MaxAddress = (ULONG_PTR)SystemInfo.lpMaximumApplicationAddress;
    DWORD AllocationGranularity = SystemInfo.dwAllocationGranularity;
    DWORD AllocationPageSize = SystemInfo.dwPageSize;

    /* Look only for the +/- 1GB virtual memory around */
    if (MinAddress < BaseAddress - MAX_MEMORY_RANGE && BaseAddress > MAX_MEMORY_RANGE)
        MinAddress = BaseAddress - MAX_MEMORY_RANGE;

    /* Look only for the +/- 1GB virtual memory around */
    if (MaxAddress > BaseAddress + MAX_MEMORY_RANGE)
        MaxAddress = BaseAddress + MAX_MEMORY_RANGE;

    /* Subtract 1 page size from maximum address */
    MaxAddress -= static_cast<ULONG_PTR>(AllocationPageSize) - 1;

    return VirtualAllocNearPage(
        ProcessHandle,
        Address,
        (PVOID)MinAddress,
        (PVOID)MaxAddress,
        AllocationPageSize,
        AllocationType,
        AllocationProtection,
        AllocationGranularity);
}

BOOL WINAPI IsExecutableAddress(
    IN HANDLE ProcessHandle,
    IN PVOID Address)
{
    MEMORY_BASIC_INFORMATION MemoryInfo = { 0 };

    if (VirtualQueryEx(ProcessHandle, Address, &MemoryInfo, sizeof(MemoryInfo)) != sizeof(MemoryInfo)) {
        return FALSE;
    }

    return ((MemoryInfo.State == MEM_COMMIT) && (MemoryInfo.Protect & PAGE_EXECUTE_FLAGS));
}