INT3 Vectored Exception Handler hooking

veh_hook.cpp

/**
veh_hook Vectored Exception Handler hooking library
Version: 24-March-2008
**/
#define WINVER 0x0501
#define _WIN32_WINNT 0x0501
#include <windows.h>
#include "veh_hook.h"

static veh_list_t* list = NULL;
char int3bp[] = "\xCC";

bool add_veh_hook(void* origFunc, void* newFunc, int hook_type)
{
    //static veh_list_t* list = NULL;
    DWORD oldProtect;
    if (list == NULL) list = new_veh_list();
    if (list == NULL) return false;
    void* handle = AddVectoredExceptionHandler(1, (PVECTORED_EXCEPTION_HANDLER)veh_dispatch);
    veh_node_t* newnode = insert_veh_node(list, origFunc, newFunc, handle);

    // For memory hooks especially, we need to know the address of the start of the relevant page.
    MEMORY_BASIC_INFORMATION mem_info;
    VirtualQuery(origFunc, &mem_info, sizeof(MEMORY_BASIC_INFORMATION));
    newnode->baseAddr = mem_info.BaseAddress;

    VirtualProtect(origFunc, sizeof(int), PAGE_EXECUTE_READWRITE, &newnode->OldProtect);
    memcpy((void*)(&newnode->origBaseByte), (const void*)origFunc, sizeof (BYTE));
    memcpy((void*)origFunc, (const void*)&int3bp, sizeof (BYTE));
    VirtualProtect(origFunc, sizeof(int), newnode->OldProtect, &oldProtect);
    return true;
}

bool remove_veh_hook(void* origFunc)
{
    if (list == NULL) return false;
    veh_node_t* node = get_veh_node(list, origFunc, true);
    if (node == NULL) return false;
    RemoveVectoredExceptionHandler(node->handle);
    return remove_veh_node(list, origFunc);
}

bool remove_veh_node(veh_list_t* list, void* origFunc)
{
    veh_node_t* searchnode;
    veh_node_t* lastsearchnode = NULL;
    searchnode = list->head;

    while (searchnode != NULL)
    {
        if (searchnode->origFunc == origFunc)
        {
            if (lastsearchnode == NULL)
            {
                list->head = searchnode->next;
                if (list->tail == searchnode) list->tail = searchnode->next;
            }
            else
            {
                lastsearchnode->next = searchnode->next;
            }
            free(searchnode);
            return true;
        }
        lastsearchnode = searchnode;
        searchnode = searchnode->next;
    }
    return false;
}

LONG CALLBACK veh_dispatch(PEXCEPTION_POINTERS ExceptionInfo)
{
    DWORD oldProtect;
    void* Addr = ExceptionInfo->ExceptionRecord->ExceptionAddress;
    ULONG Code = ExceptionInfo->ExceptionRecord->ExceptionCode;

    if (Code != STATUS_BREAKPOINT && Code != STATUS_SINGLE_STEP) return EXCEPTION_CONTINUE_SEARCH;
    // Try to find the node associated with the address of the current exception, continue searching for handlers if not found;
    veh_node_t* currnode = get_veh_node(list, Addr, false);
    if (currnode == NULL) return EXCEPTION_CONTINUE_SEARCH;
    DWORD hooktype = currnode->hooktype;
    // Pre-callback functions:
    if (Code == STATUS_BREAKPOINT && hooktype == VEH_HK_INT3)
    {
        //(Temporarily) remove the int3 breakpoint
        VirtualProtect(Addr, sizeof(int), PAGE_EXECUTE_READWRITE, &currnode->OldProtect);
        memcpy((void*)Addr, (const void*)(&currnode->origBaseByte), sizeof (char));
        currnode->newFunc();
        VirtualProtect(Addr, sizeof(int), currnode->OldProtect, &oldProtect);
    }
    else if (Code == STATUS_SINGLE_STEP && hooktype == VEH_HK_INT3)
    {
        // Restore the INT3 breakpoint
        VirtualProtect(Addr, sizeof(int), PAGE_EXECUTE_READWRITE, &currnode->OldProtect);
        memcpy((void*)currnode->origFunc, (const void*)&int3bp, sizeof (BYTE));
        VirtualProtect(Addr, sizeof(int), currnode->OldProtect, &oldProtect);
        ExceptionInfo->ContextRecord->EFlags &= ~0x00000100; // Remove TRACE from EFLAGS
        return EXCEPTION_CONTINUE_EXECUTION;
    }
    else if (Code == STATUS_SINGLE_STEP && hooktype == VEH_HK_HW)
    {
        currnode->newFunc();
    }
    else if (Code == STATUS_SINGLE_STEP && hooktype == VEH_HK_MEM)
    {

        currnode->newFunc();
    }
    return EXCEPTION_CONTINUE_EXECUTION;
}

veh_list_t* new_veh_list()
{
    veh_list_t* newlist = (veh_list_t*)malloc(sizeof(veh_list_t));
    if (newlist == NULL) return NULL;
    newlist->head = NULL;
    newlist->tail = NULL;
    return newlist;
}

veh_node_t* insert_veh_node(veh_list_t* list, void* origFunc, void* newFunc, void* handle)
{
    if (list == NULL) return NULL;
    /* create a new node and fill in the blanks */
    veh_node_t* newnode = (veh_node_t*)malloc(sizeof(veh_node_t));
    if (newnode == NULL) return NULL;
    newnode->origFunc = origFunc;
    newnode->newFunc = (pfvoid)newFunc;
    newnode->handle = handle;
    newnode->OldProtect = PAGE_EXECUTE_READWRITE;
    newnode->next = NULL;

    if (list->head == NULL)
    {
        list->head = newnode;
        list->tail = newnode;
    }
    else
    {
        list->tail->next = newnode;
        list->tail = newnode;
    }
    return newnode;
}

veh_node_t* get_veh_node(veh_list_t* list, void* origFunc, bool exactmatch)
{
    veh_node_t* newnode;
    veh_node_t* closestnode = NULL;
    if (list == NULL) return NULL;
    newnode = list->head;
    MEMORY_BASIC_INFORMATION mem_info;
    VirtualQuery(origFunc, &mem_info, sizeof(MEMORY_BASIC_INFORMATION));
    while (newnode != NULL)
    {

        if (newnode->origFunc == origFunc)
        {
            return newnode;
        }
        if (!exactmatch) if (newnode->baseAddr == mem_info.BaseAddress) closestnode = newnode;
        newnode = newnode->next;
    }

    return closestnode;
}

veh_hook.h

/**
veh_hook Vectored Exception Handler hooking library
Version: 24-March-2008
**/

#ifndef LIST_T_H_INCLUDED
#define LIST_T_H_INCLUDED
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>

// VEH Hooking types
#define VEH_HK_INT3 0
#define VEH_HK_MEM 1
#define VEH_HK_HW 2
// -

#define OPCODE_INT3 "\xCC"


typedef void (*pfvoid)();
typedef struct veh_node
{
	void* origFunc;
	pfvoid newFunc;
	void* handle;
	DWORD hooktype;
	void* baseAddr; // Address of the page in which origFunc resides.
	BYTE origBaseByte;
	DWORD OldProtect;
	struct veh_node* next;
} veh_node_t;

typedef struct
{
	veh_node_t* head;
	veh_node_t* tail;
} veh_list_t;

// VEH hook interface functions for creating and removing hooks.
bool add_veh_hook(void* origFunc, void* newFunc, int hook_type);
bool remove_veh_hook(void* origFunc);

// The VEH dispathing function is called by Windows every time an exception is encountered.
// the function dispatches calls to the correct inctercept function.
LONG CALLBACK veh_dispatch(PEXCEPTION_POINTERS ExceptionInfo);

// Functions used internally by the library.
veh_list_t* new_veh_list();
veh_node_t* insert_veh_node(veh_list_t* list, void* origFunc, void* newFunc, void* handle);
bool remove_veh_node(veh_list_t* list, void* origFunc);
veh_node_t* get_veh_node(veh_list_t* list, void* origFunc, bool exactmatch);

#endif // LIST_T_H_INCLUDED