Reference

memguard(9)

memory allocator for debugging purposes

NAME

MemGuard – memory allocator for debugging purposes

SYNOPSIS

options DEBUG_MEMGUARD

DESCRIPTION

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 default.

FILES

src/sys/kern/kern_malloc.c

File to replace the malloc type in

EXAMPLES

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.

SEE ALSO

sysctl(8), vmstat(8), contigmalloc(9), malloc(9)

HISTORY

MemGuard first appeared in FreeBSD 6.0.

AUTHORS

MemGuard was written by Bosko Milekic ⟨[email protected]⟩. This manual page was written by Christian Brueffer ⟨[email protected]⟩.

BUGS

Currently, it is not possible to override UMA zone(9) allocations.