hash扫描获取函数地址

前言：分析学习shellcode的时候，发现一种方法是通过HASH扫描来比较获取相关的API函数的方法，这里记录学习下

小知识点：如果大家跟过cobalt strike的话也会发现shellcode执行过程中也是通过对应的hash比较来获取函数地址的

hash扫描获取函数地址

动态获取的一般都是通过PEB遍历相关的ldr的双向链表可以直接获取，那么会为什么其中还需要通过hash来进行寻找呢？

原理

Hash寻找API地址和GetProcAddress函数实现原理大致是一样的，只不过在遍历AddressOfNames表时进行函数名对比时用的是hash，先把获取到的函数名进行hash转换，然后与我们的hash值进行比较，若一直则返回地址。

作用

通过函数的hash值来获取到某些API的内存地址，避免直接只用函数名，因为某些检测软件就是通过函数名来检测的

实现

#include <windows.h>
#include <winternl.h>
#include <stdio.h>
// This compiles to a ROR instruction
// This is needed because _lrotr() is an external reference
// Also, there is not a consistent compiler intrinsic to accomplish this across all three platforms.
#define ROTR32(value, shift)	(((DWORD) value >> (BYTE) shift) | ((DWORD) value << (32 - (BYTE) shift)))

// Redefine PEB structures. The structure definitions in winternl.h are incomplete.
typedef struct _MY_PEB_LDR_DATA {
	ULONG Length;
	BOOL Initialized;
	PVOID SsHandle;
	LIST_ENTRY InLoadOrderModuleList;
	LIST_ENTRY InMemoryOrderModuleList;
	LIST_ENTRY InInitializationOrderModuleList;
} MY_PEB_LDR_DATA, *PMY_PEB_LDR_DATA;

typedef struct _MY_LDR_DATA_TABLE_ENTRY
{
	LIST_ENTRY InLoadOrderLinks;
	LIST_ENTRY InMemoryOrderLinks;
	LIST_ENTRY InInitializationOrderLinks;
	PVOID DllBase;
	PVOID EntryPoint;
	ULONG SizeOfImage;
	UNICODE_STRING FullDllName;
	UNICODE_STRING BaseDllName;
} MY_LDR_DATA_TABLE_ENTRY, *PMY_LDR_DATA_TABLE_ENTRY;

HMODULE GetProcAddressWithHash(_In_ DWORD dwModuleFunctionHash);

int main(){
	GetProcAddressWithHash(0x726774C);
}

HMODULE GetProcAddressWithHash(_In_ DWORD dwModuleFunctionHash)
{
	PPEB PebAddress;
	PMY_PEB_LDR_DATA pLdr;
	PMY_LDR_DATA_TABLE_ENTRY pDataTableEntry;
	PVOID pModuleBase;
	PIMAGE_NT_HEADERS pNTHeader;
	DWORD dwExportDirRVA;
	PIMAGE_EXPORT_DIRECTORY pExportDir;
	PLIST_ENTRY pNextModule;
	DWORD dwNumFunctions;
	USHORT usOrdinalTableIndex;
	PDWORD pdwFunctionNameBase;
	PCSTR pFunctionName;
	UNICODE_STRING BaseDllName;
	DWORD dwModuleHash;
	DWORD dwFunctionHash;
	PCSTR pTempChar;
	DWORD i;

#if defined(_WIN64)
	PebAddress = (PPEB)__readgsqword(0x60);
#elif defined(_M_ARM)
	// I can assure you that this is not a mistake. The C compiler improperly emits the proper opcodes
	// necessary to get the PEB.Ldr address
	PebAddress = (PPEB)((ULONG_PTR)_MoveFromCoprocessor(15, 0, 13, 0, 2) + 0);
	__emit(0x00006B1B);
#else
	PebAddress = (PPEB)__readfsdword(0x30);
#endif

	pLdr = (PMY_PEB_LDR_DATA)PebAddress->Ldr;
	pNextModule = pLdr->InLoadOrderModuleList.Flink;
	pDataTableEntry = (PMY_LDR_DATA_TABLE_ENTRY)pNextModule;

	while (pDataTableEntry->DllBase != NULL)
	{
		dwModuleHash = 0;
		pModuleBase = pDataTableEntry->DllBase;
		BaseDllName = pDataTableEntry->BaseDllName;
		pNTHeader = (PIMAGE_NT_HEADERS)((ULONG_PTR)pModuleBase + ((PIMAGE_DOS_HEADER)pModuleBase)->e_lfanew);
		dwExportDirRVA = pNTHeader->OptionalHeader.DataDirectory[0].VirtualAddress;

		// Get the next loaded module entry
		pDataTableEntry = (PMY_LDR_DATA_TABLE_ENTRY)pDataTableEntry->InLoadOrderLinks.Flink;

		// If the current module does not export any functions, move on to the next module.
		if (dwExportDirRVA == 0)
		{
			continue;
		}

		// Calculate the module hash
		for (i = 0; i < BaseDllName.MaximumLength; i++)
		{
			pTempChar = ((PCSTR)BaseDllName.Buffer + i);

			dwModuleHash = ROTR32(dwModuleHash, 13);

			if (*pTempChar >= 0x61)
			{
				dwModuleHash += *pTempChar - 0x20;
			}
			else
			{
				dwModuleHash += *pTempChar;
			}
		}

		pExportDir = (PIMAGE_EXPORT_DIRECTORY)((ULONG_PTR)pModuleBase + dwExportDirRVA);

		dwNumFunctions = pExportDir->NumberOfNames;
		pdwFunctionNameBase = (PDWORD)((PCHAR)pModuleBase + pExportDir->AddressOfNames);

		for (i = 0; i < dwNumFunctions; i++)
		{
			dwFunctionHash = 0;
			pFunctionName = (PCSTR)(*pdwFunctionNameBase + (ULONG_PTR)pModuleBase);
			pdwFunctionNameBase++;

			pTempChar = pFunctionName;

			do
			{
				dwFunctionHash = ROTR32(dwFunctionHash, 13);
				dwFunctionHash += *pTempChar;
				pTempChar++;
			} while (*(pTempChar - 1) != 0);

			dwFunctionHash += dwModuleHash;

			if (dwFunctionHash == dwModuleFunctionHash)
			{
				printf("%s", pFunctionName);
				usOrdinalTableIndex = *(PUSHORT)(((ULONG_PTR)pModuleBase + pExportDir->AddressOfNameOrdinals) + (2 * i));
				return (HMODULE)((ULONG_PTR)pModuleBase + *(PDWORD)(((ULONG_PTR)pModuleBase + pExportDir->AddressOfFunctions) + (4 * usOrdinalTableIndex)));
			}
		}
	}

	// All modules have been exhausted and the function was not found.
	return NULL;
}