Ticket #885: VirtualProtect.c

#include <stdio.h>
#include <windows.h>

int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
        char * ptr;
        void (*x_ptr)();

        BOOL protected;
        DWORD last_error;
        char last_error_msg[4096];
        DWORD old_protect;
        int i;

        // allocate non-executable memory
        ptr = VirtualAlloc(NULL, 1, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
        *ptr = 0xc3; /* RET */

        x_ptr = ptr;
        /* x_ptr(); */  /* generate DEP exception */

        // convert it to executable read-write memory
        protected = VirtualProtect(ptr, 1, PAGE_EXECUTE_READWRITE, &old_protect);
        last_error = GetLastError();
        FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, NULL, last_error, 0, &last_error_msg, 4096, NULL);
        printf("%d %d %s\n", protected, last_error, last_error_msg);

        x_ptr();                /* works fine */

        // allocate non-executable memory
        ptr = VirtualAlloc(NULL, 1, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
        *ptr = 0xc3; /* RET */

        x_ptr = ptr;
        /* x_ptr(); */  /* generate DEP exception */

        // convert it to execute-only memory */
        protected = VirtualProtect(ptr, 1, PAGE_EXECUTE, &old_protect);
        FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, NULL, last_error, 0, &last_error_msg, 4096, NULL);
        printf("%d %d %s\n", protected, last_error, last_error_msg);

        x_ptr();                /* works fine */

        return 0;
}