My own implementation of a memory checker
Switch branches/tags
Nothing to show
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Permalink
Failed to load latest commit information.
mem_checker
mem_strace
mem_strace_hook
mem_tracker
AUTHORS
Makefile
README
TODO

README

  README :

    The goal of this project is to implement our own memcheck tool,
    thus a program that detects any invalid access and memory leaks.
    The project is decomposed in four levels that are describe below.

  Level 1 :

    We had to implement a simple strace, that track all syscall in the
    traced program. By the use of ptrace and its request like PTRACE_SYSCALL,
    PTRACE_GETREGS and so on. In this level i didn't manage to follow the child
    on fork.

  Level 2 :

    I spent many time on this level that aimed to reproduce an strace like, thus
    tracing the syscall in the tracee. However, we had to break on every syscall in
    order to get the control and retrieve information like the syscall num.
    Once the r_debug structure is obtained, we have access to the link map. So i
    just go through the link_map structure and loaded in a map of map container.
    I used a map of map because, i stored the name of the loaded object name,
    the address of the breakpoint and the instruction before setting the breakpoint.
    The process to load the library i used is : open in the file system, the concerned
    library, go through the elf to retrieve the section header, then disasssemble
    all the executable section, retrieve the address of all syscall instruction, and
    finally store this address and replace the instruction by a breakpoint.
    Conclusion, by breaking on syscall and r_brk i know i should examine a syscall
    or add/delete library.

  Level 3:

    In the level 3, i just had to track memory allocation, deallocation and
    protection. I wrote i library that will be preload by the traced program
    before its execution. In this library, malloc, calloc, realloc and free are
    redefine. So each time the traced programm will call one of this function
    , redefinition in my own library will be called. So by writting a wrapper
    i can retrieve all information i want on the call and store structure that
    represente the allocation in case of a malloc for exemple. The process
    used to communicate with the tracer was : set a register with a magic number
    in the function in the library, set other register with information we want
    like the size, and add int3; all of this in assembly inline. By catching the
    SIGTRAP send by the breakpoint and check the value of the different registers,
    i can get every information i need on the call. For mmap, munmap, mremap and
    mprotect nothing special but catching the corresponding syscall num is done.
    I implemented the bonus for splitting in this threshold.

  Level 4:

    The goal of this threshold was to make our program acts like a memory checker.
    I manage to detect invalid access in mapping memory when it was directly allocated
    by mmap, numbers of leaks but it seems like my program isn't really accurate.
    However i didn't success to detect invalid read or write directly in the heap,
    my implementation of this feature lead to huge false positive invalid access.
    So i decided to keep the safer one.