• How to Make Any Process Work With Transactional NTFS: My First Step to Writing a Sandbox for Windows

      TransactionMaster One of the modules in the Windows kernel provides support for combining a set of file operations into an entity known as a transaction. Just like in databases, these entities are isolated and atomic. You can make some changes to the file system that won't be visible outside until you commit them. Or, as an alternative, you can always rollback everything. In any case, you act upon the group of operations as a whole. Precisely what needed to preserve consistency while installing software or updating our systems, right? If something goes wrong — the installer or even the whole system crashes — the transaction rolls back automatically.

      From the very first time I saw an article about this incredible mechanism, I always wondered how the world would look like from the inside. And you know what? I just discovered a truly marvelous approach to force any process to operate within a predefined transaction, which this margin is too narrow to contain. Furthermore, most of the time, it does not even require administrative privileges.

      Let's then talk about Windows internals, try out a new tool, and answer one question: what does it have to do with sandboxes?

      Read more →
    • My Pascal compiler and Polish contemporary art


        Several years ago I wrote a Pascal compiler. The motivation was simple: as a teenager, I had learnt from my first programming textbooks that a compiler is a very sophisticated thing. This claim eventually became a challenge and required to be tested by experience.


        First, a simplistic PL/0 compiler came into being, and later an almost fully-functional Pascal compiler for MS-DOS has grown from it. My source of inspiration was the Compiler Construction book by Niklaus Wirth, the inventor of the Pascal language. I don't care if Wirth's views are now considered obsolete and have no direct connections to the IT mainstream, or if the compiler design fashion has changed. It is enough to know that his techniques are still simple, elegant, and — last but not least — bring much fun, since it is more appealing to parse a program source with a handwritten recursive descent parser and generate the machine code, rather than to call yaccs, bisons and all their descendants.

        My compiler's fate was not so trivial. It has lived two lives: the first one in my own hands, and the second in the hands of computer antiquarians from Poland.
        Read more →