Provided by: freebsd-manpages_6.2-1_all
MemGuard - memory allocator for debugging purposes
MemGuard is a simple and small replacement memory allocator designed to
help detect tamper-after-free scenarios. These problems are more and
more common and likely with multithreaded kernels where race conditions
are more prevalent.
Currently, MemGuard can only take over malloc(), realloc() and free() for
a particular malloc type. MemGuard takes over M_SUBPROC allocations by
src/sys/kern/kern_malloc.c File to replace the malloc type in
The following steps are necessary to use MemGuard:
1. Put the DEBUG_MEMGUARD option into your kernel config.
2. Open src/sys/kern/kern_malloc.c in your favourite editor. Look for
lines containing “XXX CHANGEME!” and replace M_SUBPROC with the
appropriate malloc type. This might require additional but
small/simple code modifications (e.g., if the malloc type is
declared out of scope).
3. Build and install your kernel. Tune the vm.memguard_divisor boot-
time tunable, which is used to scale how much of kmem_map you want
to allot for MemGuard. The default is 10, so kmem_size/10 bytes
will be used. The kmem_size value can be obtained via the
vm.kmem_size sysctl(8) variable.
sysctl(8), vmstat(8), contigmalloc(9), malloc(9)
MemGuard first appeared in FreeBSD 6.0.
MemGuard was written by Bosko Milekic 〈bmilekic@FreeBSD.org〉. This
manual page was written by Christian Brueffer 〈brueffer@FreeBSD.org〉.
Currently, it is not possible to override UMA zone(9) allocations.