MEMGUARD(9) MidnightBSD Kernel Developer’s Manual MEMGUARD(9)

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.

EXAMPLES

To use MemGuard for memory type compiled into the kernel, one has to add the following line to the /boot/loader.conf:

vm.memguard.desc=<memory_type>

Where memory_type is a short description of memory type to monitor. The short description of memory type is the second argument to MALLOC_DEFINE(9), so one has to find it in the kernel source.

To use MemGuard for memory type defined in a kernel module, one has to set vm.memguard.desc sysctl(8) variable before loading the module:

sysctl vm.memguard.desc=<memory_type>

The vm.memguard.divisor boot-time tunable is used to scale how much of kmem_map one wants to allocate 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), redzone(9)

HISTORY

MemGuard first appeared in FreeBSD 6.0.

AUTHORS

MemGuard was written by Bosko Milekic 〈bmilekic@FreeBSD.org〉. This manual page was written by Christian Brueffer 〈brueffer@FreeBSD.org〉.

BUGS

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

MidnightBSD 0.3 January 31, 2006 MidnightBSD 0.3