.\" Copyright (c) 2005 Christian Brueffer .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" $FreeBSD: releng/12.0/share/man/man9/memguard.9 315803 2017-03-23 06:08:01Z ngie $ .\" .Dd March 22, 2017 .Dt MEMGUARD 9 .Os .Sh NAME .Nm MemGuard .Nd "memory allocator for debugging purposes" .Sh SYNOPSIS .Cd "options DEBUG_MEMGUARD" .Sh DESCRIPTION .Nm 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. .Pp .Nm can take over .Fn malloc , .Fn realloc and .Fn free for a single malloc type. Alternatively .Nm can take over .Fn uma_zalloc , .Fn uma_zalloc_arg and .Fn uma_free for a single .Xr uma 9 zone. Also .Nm can guard all allocations larger than .Dv PAGE_SIZE , and can guard a random fraction of all allocations. There is also a knob to prevent allocations smaller than a specified size from being guarded, to limit memory waste. .Sh EXAMPLES To use .Nm for a memory type, either add an entry to .Pa /boot/loader.conf : .Bd -literal -offset indent vm.memguard.desc= .Ed .Pp Or set the .Va vm.memguard.desc .Xr sysctl 8 variable at run-time: .Bd -literal -offset indent sysctl vm.memguard.desc= .Ed .Pp Where .Ar memory_type can be either a short description of the memory type to monitor, either name of .Xr uma 9 zone. Only allocations from that .Ar memory_type made after .Va vm.memguard.desc is set will potentially be guarded. If .Va vm.memguard.desc is modified at run-time then only allocations of the new .Ar memory_type will potentially be guarded once the .Xr sysctl 8 is set. Existing guarded allocations will still be properly released by either .Xr free 9 or .Xr uma_zfree 9 , depending on what kind of allocation was taken over. .Pp To determine short description of a .Xr malloc 9 type one can either take it from the first column of .Xr vmstat 8 Fl m output, or to find it in the kernel source. It is the second argument to .Xr MALLOC_DEFINE 9 macro. To determine name of .Xr uma 9 zone one can either take it from the first column of .Xr vmstat 8 Fl z output, or to find it in the kernel source. It is the first argument to the .Xr uma_zcreate 9 function. .Pp The .Va vm.memguard.divisor boot-time tunable is used to scale how much of the system's physical memory .Nm is allowed to consume. The default is 10, so up to .Va vm_cnt.v_page_count Ns /10 pages can be used. .Nm will reserve .Va vm_kmem_max / .Va vm.memguard.divisor bytes of virtual address space, limited by twice the physical memory size. The physical limit is reported as .Va vm.memguard.phys_limit and the virtual space reserved for .Nm is reported as .Va vm.memguard.mapsize . .Pp .Nm will not do page promotions for any allocation smaller than .Va vm.memguard.minsize bytes. The default is 0, meaning all allocations can potentially be guarded. .Nm can guard sufficiently large allocations randomly, with average frequency of every one in 100000 / .Va vm.memguard.frequency allocations. The default is 0, meaning no allocations are randomly guarded. .Pp .Nm can optionally add unmapped guard pages around each allocation to detect overflow and underflow, if .Va vm.memguard.options has the 1 bit set. This option is enabled by default. .Nm will optionally guard all allocations of .Dv PAGE_SIZE or larger if .Va vm.memguard.options has the 2 bit set. This option is off by default. By default .Nm does not guard .Xr uma 9 zones that have been initialized with the .Dv UMA_ZONE_NOFREE flag set, since it can produce false positives on them. However, this safety measure can be turned off by setting bit 3 of the .Va vm.memguard.options tunable. .Sh SEE ALSO .Xr sysctl 8 , .Xr vmstat 8 , .Xr contigmalloc 9 , .Xr malloc 9 , .Xr redzone 9 , .Xr uma 9 .Sh HISTORY .Nm first appeared in .Fx 6.0 . .Sh AUTHORS .An -nosplit .Nm was originally written by .An Bosko Milekic Aq Mt bmilekic@FreeBSD.org . This manual page was originally written by .An Christian Brueffer Aq Mt brueffer@FreeBSD.org . Additions have been made by .An Matthew Fleming Aq Mt mdf@FreeBSD.org and .An Gleb Smirnoff Aq Mt glebius@FreeBSD.org to both the implementation and the documentation.