syscalls.nim

{.passC:"-masm=intel".}

type
  PS_ATTR_UNION* {.pure, union.} = object
    Value*: ULONG
    ValuePtr*: PVOID
  PS_ATTRIBUTE* {.pure.} = object
    Attribute*: ULONG 
    Size*: SIZE_T
    u1*: PS_ATTR_UNION
    ReturnLength*: PSIZE_T
  PPS_ATTRIBUTE* = ptr PS_ATTRIBUTE
  PS_ATTRIBUTE_LIST* {.pure.} = object
    TotalLength*: SIZE_T
    Attributes*: array[2, PS_ATTRIBUTE]
  PPS_ATTRIBUTE_LIST* = ptr PS_ATTRIBUTE_LIST
  KNORMAL_ROUTINE* {.pure.} = object
    NormalContext*: PVOID
    SystemArgument1*: PVOID
    SystemArgument2*: PVOID
  PKNORMAL_ROUTINE* = ptr KNORMAL_ROUTINE

{.emit: """
#pragma once

// Code below is adapted from @modexpblog. Read linked article for more details.
// https://www.mdsec.co.uk/2020/12/bypassing-user-mode-hooks-and-direct-invocation-of-system-calls-for-red-teams

#ifndef SW2_HEADER_H_
#define SW2_HEADER_H_

#include <windows.h>

#define SW2_SEED 0xC37D1755
#define SW2_ROL8(v) (v << 8 | v >> 24)
#define SW2_ROR8(v) (v >> 8 | v << 24)
#define SW2_ROX8(v) ((SW2_SEED % 2) ? SW2_ROL8(v) : SW2_ROR8(v))
#define SW2_MAX_ENTRIES 500
#define SW2_RVA2VA(Type, DllBase, Rva) (Type)((ULONG_PTR) DllBase + Rva)

// Typedefs are prefixed to avoid pollution.

typedef struct _SW2_SYSCALL_ENTRY
{
    DWORD Hash;
    DWORD Address;
} SW2_SYSCALL_ENTRY, *PSW2_SYSCALL_ENTRY;

typedef struct _SW2_SYSCALL_LIST
{
    DWORD Count;
    SW2_SYSCALL_ENTRY Entries[SW2_MAX_ENTRIES];
} SW2_SYSCALL_LIST, *PSW2_SYSCALL_LIST;

typedef struct _SW2_PEB_LDR_DATA {
	BYTE Reserved1[8];
	PVOID Reserved2[3];
	LIST_ENTRY InMemoryOrderModuleList;
} SW2_PEB_LDR_DATA, *PSW2_PEB_LDR_DATA;

typedef struct _SW2_LDR_DATA_TABLE_ENTRY {
	PVOID Reserved1[2];
	LIST_ENTRY InMemoryOrderLinks;
	PVOID Reserved2[2];
	PVOID DllBase;
} SW2_LDR_DATA_TABLE_ENTRY, *PSW2_LDR_DATA_TABLE_ENTRY;

typedef struct _SW2_PEB {
	BYTE Reserved1[2];
	BYTE BeingDebugged;
	BYTE Reserved2[1];
	PVOID Reserved3[2];
	PSW2_PEB_LDR_DATA Ldr;
} SW2_PEB, *PSW2_PEB;

DWORD SW2_HashSyscall(PCSTR FunctionName);
BOOL SW2_PopulateSyscallList();
EXTERN_C DWORD SW2_GetSyscallNumber(DWORD FunctionHash);

#endif


// Code below is adapted from @modexpblog. Read linked article for more details.
// https://www.mdsec.co.uk/2020/12/bypassing-user-mode-hooks-and-direct-invocation-of-system-calls-for-red-teams

SW2_SYSCALL_LIST SW2_SyscallList = {0,1};

DWORD SW2_HashSyscall(PCSTR FunctionName)
{
    DWORD i = 0;
    DWORD Hash = SW2_SEED;

    while (FunctionName[i])
    {
        WORD PartialName = *(WORD*)((ULONG64)FunctionName + i++);
        Hash ^= PartialName + SW2_ROR8(Hash);
    }

    return Hash;
}

BOOL SW2_PopulateSyscallList()
{
    // Return early if the list is already populated.
    if (SW2_SyscallList.Count) return TRUE;

    PSW2_PEB Peb = (PSW2_PEB)__readgsqword(0x60);
    PSW2_PEB_LDR_DATA Ldr = Peb->Ldr;
    PIMAGE_EXPORT_DIRECTORY ExportDirectory = NULL;
    PVOID DllBase = NULL;

    // Get the DllBase address of NTDLL.dll. NTDLL is not guaranteed to be the second
    // in the list, so it's safer to loop through the full list and find it.
    PSW2_LDR_DATA_TABLE_ENTRY LdrEntry;
    for (LdrEntry = (PSW2_LDR_DATA_TABLE_ENTRY)Ldr->Reserved2[1]; LdrEntry->DllBase != NULL; LdrEntry = (PSW2_LDR_DATA_TABLE_ENTRY)LdrEntry->Reserved1[0])
    {
        DllBase = LdrEntry->DllBase;
        PIMAGE_DOS_HEADER DosHeader = (PIMAGE_DOS_HEADER)DllBase;
        PIMAGE_NT_HEADERS NtHeaders = SW2_RVA2VA(PIMAGE_NT_HEADERS, DllBase, DosHeader->e_lfanew);
        PIMAGE_DATA_DIRECTORY DataDirectory = (PIMAGE_DATA_DIRECTORY)NtHeaders->OptionalHeader.DataDirectory;
        DWORD VirtualAddress = DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress;
        if (VirtualAddress == 0) continue;

        ExportDirectory = (PIMAGE_EXPORT_DIRECTORY)SW2_RVA2VA(ULONG_PTR, DllBase, VirtualAddress);

        // If this is NTDLL.dll, exit loop.
        PCHAR DllName = SW2_RVA2VA(PCHAR, DllBase, ExportDirectory->Name);

        if ((*(ULONG*)DllName | 0x20202020) != 'ldtn') continue;
        if ((*(ULONG*)(DllName + 4) | 0x20202020) == 'ld.l') break;
    }

    if (!ExportDirectory) return FALSE;

    DWORD NumberOfNames = ExportDirectory->NumberOfNames;
    PDWORD Functions = SW2_RVA2VA(PDWORD, DllBase, ExportDirectory->AddressOfFunctions);
    PDWORD Names = SW2_RVA2VA(PDWORD, DllBase, ExportDirectory->AddressOfNames);
    PWORD Ordinals = SW2_RVA2VA(PWORD, DllBase, ExportDirectory->AddressOfNameOrdinals);

    // Populate SW2_SyscallList with unsorted Zw* entries.
    DWORD i = 0;
    PSW2_SYSCALL_ENTRY Entries = SW2_SyscallList.Entries;
    do
    {
        PCHAR FunctionName = SW2_RVA2VA(PCHAR, DllBase, Names[NumberOfNames - 1]);

        // Is this a system call?
        if (*(USHORT*)FunctionName == 'wZ')
        {
            Entries[i].Hash = SW2_HashSyscall(FunctionName);
            Entries[i].Address = Functions[Ordinals[NumberOfNames - 1]];

            i++;
            if (i == SW2_MAX_ENTRIES) break;
        }
    } while (--NumberOfNames);

    // Save total number of system calls found.
    SW2_SyscallList.Count = i;

    // Sort the list by address in ascending order.
    for (DWORD i = 0; i < SW2_SyscallList.Count - 1; i++)
    {
        for (DWORD j = 0; j < SW2_SyscallList.Count - i - 1; j++)
        {
            if (Entries[j].Address > Entries[j + 1].Address)
            {
                // Swap entries.
                SW2_SYSCALL_ENTRY TempEntry;

                TempEntry.Hash = Entries[j].Hash;
                TempEntry.Address = Entries[j].Address;

                Entries[j].Hash = Entries[j + 1].Hash;
                Entries[j].Address = Entries[j + 1].Address;

                Entries[j + 1].Hash = TempEntry.Hash;
                Entries[j + 1].Address = TempEntry.Address;
            }
        }
    }

    return TRUE;
}

EXTERN_C DWORD SW2_GetSyscallNumber(DWORD FunctionHash)
{
    // Ensure SW2_SyscallList is populated.
    if (!SW2_PopulateSyscallList()) return -1;

    for (DWORD i = 0; i < SW2_SyscallList.Count; i++)
    {
        if (FunctionHash == SW2_SyscallList.Entries[i].Hash)
        {
            return i;
        }
    }

    return -1;
}

""".}




proc NtWriteVirtualMemory*(ProcessHandle: HANDLE, BaseAddress: PVOID, Buffer: PVOID, NumberOfBytesToWrite: SIZE_T, NumberOfBytesWritten: PSIZE_T): NTSTATUS {.asmNoStackFrame.} =
    asm """
	mov [rsp +8], rcx          
	mov [rsp+16], rdx
	mov [rsp+24], r8
	mov [rsp+32], r9
	sub rsp, 0x28
	mov ecx, 0x08B19978D
	call SW2_GetSyscallNumber  
	add rsp, 0x28
	mov rcx, [rsp +8]          
	mov rdx, [rsp+16]
	mov r8, [rsp+24]
	mov r9, [rsp+32]
	mov r10, rcx
	nop
	syscall                    
	ret
    """

proc NtAllocateVirtualMemory*(ProcessHandle: HANDLE, BaseAddress: PVOID, ZeroBits: ULONG, RegionSize: PSIZE_T, AllocationType: ULONG, Protect: ULONG): NTSTATUS {.asmNoStackFrame.} =
    asm """
	mov [rsp +8], rcx          
	mov [rsp+16], rdx
	mov [rsp+24], r8
	mov [rsp+32], r9
	sub rsp, 0x28
	mov ecx, 0x019991F17
	call SW2_GetSyscallNumber  
	add rsp, 0x28
	mov rcx, [rsp +8]          
	mov rdx, [rsp+16]
	mov r8, [rsp+24]
	mov r9, [rsp+32]
	mov r10, rcx
	nop
	syscall                    
	ret
    """

proc NtProtectVirtualMemory*(ProcessHandle: HANDLE, BaseAddress: PVOID, RegionSize: PSIZE_T, NewProtect: ULONG, OldProtect: PULONG): NTSTATUS {.asmNoStackFrame.} =
    asm """
	mov [rsp +8], rcx          
	mov [rsp+16], rdx
	mov [rsp+24], r8
	mov [rsp+32], r9
	sub rsp, 0x28
	mov ecx, 0x003950907
	call SW2_GetSyscallNumber  
	add rsp, 0x28
	mov rcx, [rsp +8]          
	mov rdx, [rsp+16]
	mov r8, [rsp+24]
	mov r9, [rsp+32]
	mov r10, rcx
	nop
	syscall                    
	ret
    """

proc NtOpenProcess*(ProcessHandle: PHANDLE, DesiredAccess: ACCESS_MASK, ObjectAttributes: POBJECT_ATTRIBUTES, ClientId: PCLIENT_ID): NTSTATUS {.asmNoStackFrame.} =
    asm """
	mov [rsp +8], rcx          
	mov [rsp+16], rdx
	mov [rsp+24], r8
	mov [rsp+32], r9
	sub rsp, 0x28
	mov ecx, 0x0EDAFCA3F
	call SW2_GetSyscallNumber  
	add rsp, 0x28
	mov rcx, [rsp +8]          
	mov rdx, [rsp+16]
	mov r8, [rsp+24]
	mov r9, [rsp+32]
	mov r10, rcx
	nop
	syscall                    
	ret
    """

proc NtQueueApcThread*(ThreadHandle: HANDLE, ApcRoutine: PKNORMAL_ROUTINE, ApcArgument1: PVOID, ApcArgument2: PVOID, ApcArgument3: PVOID): NTSTATUS {.asmNoStackFrame.} =
    asm """
	mov [rsp +8], rcx          
	mov [rsp+16], rdx
	mov [rsp+24], r8
	mov [rsp+32], r9
	sub rsp, 0x28
	mov ecx, 0x0E24CEAEF
	call SW2_GetSyscallNumber  
	add rsp, 0x28
	mov rcx, [rsp +8]          
	mov rdx, [rsp+16]
	mov r8, [rsp+24]
	mov r9, [rsp+32]
	mov r10, rcx
	nop
	syscall                    
	ret
    """

proc NtAlertResumeThread*(ThreadHandle: HANDLE, PreviousSuspendCount: PULONG): NTSTATUS {.asmNoStackFrame.} =
    asm """
	mov [rsp +8], rcx          
	mov [rsp+16], rdx
	mov [rsp+24], r8
	mov [rsp+32], r9
	sub rsp, 0x28
	mov ecx, 0x0667614E0
	call SW2_GetSyscallNumber  
	add rsp, 0x28
	mov rcx, [rsp +8]          
	mov rdx, [rsp+16]
	mov r8, [rsp+24]
	mov r9, [rsp+32]
	mov r10, rcx
	nop
	syscall                    
	ret
    """

proc NtClose*(Handle: HANDLE): NTSTATUS {.asmNoStackFrame.} =
    asm """
	mov [rsp +8], rcx          
	mov [rsp+16], rdx
	mov [rsp+24], r8
	mov [rsp+32], r9
	sub rsp, 0x28
	mov ecx, 0x0088A6285
	call SW2_GetSyscallNumber  
	add rsp, 0x28
	mov rcx, [rsp +8]          
	mov rdx, [rsp+16]
	mov r8, [rsp+24]
	mov r9, [rsp+32]
	mov r10, rcx
	nop
	syscall                    
	ret
    """

proc NtCreateThreadEx*(ThreadHandle: PHANDLE, DesiredAccess: ACCESS_MASK, ObjectAttributes: POBJECT_ATTRIBUTES, ProcessHandle: HANDLE, StartRoutine: PVOID, Argument: PVOID, CreateFlags: ULONG, ZeroBits: SIZE_T, StackSize: SIZE_T, MaximumStackSize: SIZE_T, AttributeList: PPS_ATTRIBUTE_LIST): NTSTATUS {.asmNoStackFrame.} =
    asm """
	mov [rsp +8], rcx          
	mov [rsp+16], rdx
	mov [rsp+24], r8
	mov [rsp+32], r9
	sub rsp, 0x28
	mov ecx, 0x0C85E88A6
	call SW2_GetSyscallNumber  
	add rsp, 0x28
	mov rcx, [rsp +8]          
	mov rdx, [rsp+16]
	mov r8, [rsp+24]
	mov r9, [rsp+32]
	mov r10, rcx
	nop
	syscall                    
	ret
    """

proc NtWaitForSingleObject*(ObjectHandle: HANDLE, Alertable: BOOLEAN, TimeOut: PLARGE_INTEGER): NTSTATUS {.asmNoStackFrame.} =
    asm """
	mov [rsp +8], rcx          
	mov [rsp+16], rdx
	mov [rsp+24], r8
	mov [rsp+32], r9
	sub rsp, 0x28
	mov ecx, 0x008A92015
	call SW2_GetSyscallNumber  
	add rsp, 0x28
	mov rcx, [rsp +8]          
	mov rdx, [rsp+16]
	mov r8, [rsp+24]
	mov r9, [rsp+32]
	mov r10, rcx
	nop
	syscall                    
	ret
    """