~jkaivo/mapalloc

a memory-mapping backed allocator
document how to use the wrapper
munmap() extra pages during realloc()
f94c3b21 — Jakob Kaivo 2 years ago
add MA_abort() to unify undefined behavior path

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#MapAlloc

MapAlloc is a memory mapping based allocator with an API compatible with the C <stdlib.h> dynamic memory functions. By using memory mappings for each allocation, MapAlloc is able to provide guard pages to detect heap overflow and underflow, as well as potentially identifying use-after-free or double-free errors (in all cases, your program will crash, which is preferable to being silently exploited).

MapAlloc also maintains metadata independently from the heap, so it eliminates an entire class of vulnerabilities which rely on easy access to this metadata.

#Building

Just run make. This will give you libmapalloc.a, which you can statically link into your own programs, as well as libwrapalloc.so, which can be used with LD_PRELOAD to override your standard C library's dynamic memory functions.

#Including in your program

In your source file:

#include "mapalloc.h"

This will give you:

void *MA_malloc(size_t n);
void *MA_calloc(size_t nelem, size_t elsize);
void *MA_realloc(void *ptr, size_t n);
void MA_free(void *ptr);

Or, you can ask for macros to provide the same interfaces as <stdlib.h> (note that if you need to also include <stdlib.h>, you should include it before "mapalloc.h"):

#define MA_OVERRIDE_STDLIB
#include "mapalloc.h"

This will give you access to the same set of functions as above, but also provide macros:

#define malloc(n)	MA_malloc(n)
#define calloc(n, e)	MA_calloc(n, e)
#define realloc(p, n)	MA_realloc(p, n)
#define free(p)		MA_free(p)

Link your program with -lmapalloc (you may also need to specify -L with the path to where libmapalloc.a is if you don't copy it to part of your linker's default search path).

#Wrapper

The dynamic library libwrapalloc.so is also built by default. This can be used to wrap the standard libc functions malloc(), calloc(), realloc(), and free() to their MapAlloc equivalents if your dynamic linker supports this. For example, on Linux systems with the GNU linker:

LD_PRELOAD=libwrapalloc.so command args...