Windows on Arm64, x86/x64 emulation

[DavidXanatos]

i was somehow under the impression the article was older, but you seam to be right, it was may be a bot to late yesterday, LOL
downloading the newest WDk right now....

[sh3dow]

Originally Posted by DavidXanatos

I already have found this: https://ffri.github.io/ProjectChameleon/new_reloc_chpev2/ but its from 2019 i imagine by now there should be more refined information available?

Actually it's not that old and very recent. it was published 2021/07/13. so I don't think a lot of things has changed if any at all in this short time window knowing Microsoft.

Also the author claimed while the title says "Windows 10 on Arm" but the results are also valid in Windows 11 on Arm. probably that an evidence at the slowness of MS side of adding new features.

No new public refined information so far and he is the only public researcher known in doing research in this subject. Actually I recommend you to contact him. I'm sure he will be delighted that another reverse engineer is interested in his research and that will spark an interesting chat in this subject, I'm sure you will get a lot of info and questions answered.

[DavidXanatos]

Indeed I should contact him, good idea

But now lets talk about what we can get from the relevant header files: ...\10.0.22000.0\um\winnt.h and ...\10.0.22000.0\km\ntimage.h

With the attached FindDllExport we can extract exports from a loaded image with the below example we run a arm64 process and target a x64 process. For ourselves we get the normal ntdll.dll!LdrLoadDll while for the x64 process we get the ntdll.dll!EXP+#LdrLoadDll

	//ntdllBase 0x00007ffa5a7d0000
	//0x00007ffa5a811050 {ntdll.dll!LdrLoadDll(void)}
	//0x00007ffa5a7d1890 {ntdll.dll!EXP+#LdrLoadDll}
	//0x00007ffa5a969920 {ntdll.dll!#LdrLoadDll}

	HMODULE hNtdll = GetModuleHandle(L"ntdll.dll");
	//DWORD64 LLW1 = GetProcAddress(hNtdll, "LdrLoadDll");
	DWORD64 LLW1 = FindDllExport(GetCurrentProcess(), (DWORD64)hNtdll, "LdrLoadDll");

	DWORD64 ntdllBase = FindDllBase(hProcess, L"\\system32\\ntdll.dll");
	DWORD64 LLW2 = FindDllExport(hProcess, ntdllBase, "LdrLoadDll");

The export directory on disk (or in the arm64 case) is at RVA 0x31E1A0
for the x64 process the value at 0x178 is overwritten with 0x308810 what is the alternative export directory.
This operation is indicated by PE Anatomist in "Loader Config -> Dyn. Value Relocs", 2nd entry. So if we don't have a loaded process we could extract the value from there and read the second export directory from disk directly.

In "Debug->POGO" we see that the export directory starts at 0x308810 and is 0x2b224 in size
First the alternative directory 0x308810 to 0x31E1A0
and given the entry size it seams the primary starting at 0x31E1A0 goes to 0x333A34 booth are similar in size, so there does not seam to be a 3rd one for the ntdll.dll!#.... exports

I assume that's because there is no typical use case where a process would want those directly, a arm64 will load the primary table a x64 process the alternative table, and 32 bit once have their own ntdll's in the wow folders.

So where do we go from here, we notice that "Loader Config -> hybrid PE -> WoW Thunks Metadata" seams to hold all the RVA's we get from the export directory, and the destinations are the addresses of the #... functions.

So we can get the !EXP+#... function addresses form the export dir and look up the #... addresses in this RedirectionMetadata table, the FindDllExport now checks if the first char is a '#' and if so triggers the additional lookup.

	DWORD64 LLW3 = FindDllExport(hProcess, ntdllBase, "#LdrLoadDll");

Gives us now the right #... function address which we can use as target for arm64 code injection as well as for function calls from the injected shell code.


One thing I haven't figured yet out is how we get the alternative export directory if we don't have a process with emulation at at our disposal.
I'm not sure how PE Anatomist gets the "Dyn. Value Relocs" from, for me in a live process DynamicValueRelocTable is NULL and base + DynamicValueRelocTableOffset or loaderConfig + DynamicValueRelocTableOffset do not seam to result in valid data.
While for the use case at hand its not required I would like to know how to get to this list as well, any tips would be greatly appreciated.

[DavidXanatos]

So a small progress report on my arm64/x64 code injection experiments:
Injecting a arm64ec library into a x64 or arm64ec process on arm64 works just fine, including calling an exported function from the injected shell code. One just need to take care of calling the # function address and not the !EXP+# as given by LdrGetProcedureAddress.

Injecting a x64 library into a x64 or arm64ec process on arm64 also works just fine.
What does not yet work is calling a exported x64 function. I assume some additional code for arm64 to x64 transition needs to be added to the call.

Also the next BIG problem there is no arm32ec tool chain available.
I presume arm shell code to just load a x86 dll will work, but if one wants to call some exported function (instead of just relaying on the DllMain entry point) the arm to x86 transition will need to be researched.

What's also probably a bit of an issue, PEAnatomist does not show any "WoW Thunks Metadata" for the hybrid 32 bit ntdll in SyChpe32, while a stack trace to a statically loaded dll's DllMain shows the presence of # functions.
So there will be some investigation needed if these data can still be obtained form the image. Alternatively parsing the !EXP+# thunk should allow one to find the right # address.

[DavidXanatos]

I have figured out how to get the Dyn. Relocs Table with which we can get the alternate export directory from an image on disk:

			IMAGE_LOAD_CONFIG_DIRECTORY64 LoadConfig;

			IMAGE_DATA_DIRECTORY* dir10 = &opt_hdr_64->DataDirectory[IMAGE_DIRECTORY_ENTRY_LOAD_CONFIG];
			if (resolve_ec && dir10->VirtualAddress && dir10->Size >= FIELD_OFFSET(IMAGE_LOAD_CONFIG_DIRECTORY64, CHPEMetadataPointer) + sizeof(ULONGLONG)) {

				status = ReadDll(hProcess, FindImagePosition(dir10->VirtualAddress, nt_hdrs_64, DllBase), &LoadConfig, min(sizeof(LoadConfig), dir10->Size), NULL);
			}

			typedef struct _DYN_RELOC_TABLE {
				ULONG Unknown1;
				ULONG Unknown2;
				ULONG Unknown3;
				ULONG Unknown4;
				ULONG TableSize;
				UCHAR Entries[];
			} DYN_RELOC_TABLE;
			
			DYN_RELOC_TABLE* DynamicValueRelocTable = NULL;

			if (DllBase == 0 && (resolve_ec || resolve_exp)) { // only for images on disk, on linve images we take the actuallly used export directory

				PIMAGE_SECTION_HEADER section = IMAGE_FIRST_SECTION(nt_hdrs);
				nt_hdrs->FileHeader.NumberOfSections;

				section += (LoadConfig.DynamicValueRelocTableSection - 1);

				ULONG pos = FindImagePosition(section->VirtualAddress, nt_hdrs_64, DllBase);
				status = ReadDll(hProcess, pos, Buffer2, min(sizeof(Buffer2), section->Misc.VirtualSize), NULL);

				DynamicValueRelocTable = (DYN_RELOC_TABLE*)(Buffer2 + LoadConfig.DynamicValueRelocTableOffset);

				//dir0->VirtualAddress = 0x308810;
			}

			for (UCHAR* TablePtr = DynamicValueRelocTable->Entries; TablePtr < DynamicValueRelocTable->Entries + DynamicValueRelocTable->TableSize; ) {

				struct {
					ULONG Offset;
					ULONG Size;
				} *Section = TablePtr;
				TablePtr += 8;
				Section->Size -= 8;

				for (UCHAR* EntryPtr = TablePtr; TablePtr < EntryPtr + Section->Size; ) {
					struct {
						USHORT  
							RVA : 12,
							Unknown: 1,
							Size : 3;
					} *Entry = TablePtr;
					TablePtr += 2;

					ULONGLONG Value = 0;
					memcpy(&Value, TablePtr, Entry->Size);
					TablePtr += Entry->Size;

					DbgPrintf("%08x -> %08x\n", Section->Offset + Entry->RVA, (ULONG)Value);

				}
			}

there are a couple unknown values so if anyone has an idea what they are please share.

[DavidXanatos]

And here an other useful nugget of information: https://docs.microsoft.com/en-us/windows/uwp/porting/arm64ec-abi