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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.