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32 .Nd "memory allocator for debugging purposes"
34 .Cd "options DEBUG_MEMGUARD"
37 is a simple and small replacement memory allocator designed
38 to help detect tamper-after-free scenarios.
39 These problems are more and more common and likely with
40 multithreaded kernels where race conditions are more prevalent.
48 for a single malloc type.
61 can guard all allocations larger than
63 and can guard a random fraction of all allocations.
64 There is also a knob to prevent allocations smaller than a specified
65 size from being guarded, to limit memory waste.
69 for a memory type, either add an entry to
70 .Pa /boot/loader.conf :
71 .Bd -literal -offset indent
72 vm.memguard.desc=<memory_type>
79 .Bd -literal -offset indent
80 sysctl vm.memguard.desc=<memory_type>
85 can be either a short description of the memory type to monitor,
89 Only allocations from that
93 is set will potentially be guarded.
96 is modified at run-time then only allocations of the new
98 will potentially be guarded once the
101 Existing guarded allocations will still be properly released by
106 depending on what kind of allocation was taken over.
108 To determine short description of a
110 type one can either take it from the first column of
112 output, or to find it in the kernel source.
113 It is the second argument to
118 zone one can either take it from the first column of
120 output, or to find it in the kernel source.
121 It is the first argument to the
126 .Va vm.memguard.divisor
127 boot-time tunable is used to scale how much of the system's physical
130 is allowed to consume.
131 The default is 10, so up to
132 .Va vm_cnt.v_page_count Ns /10
138 .Va vm.memguard.divisor
139 bytes of virtual address space, limited by twice the physical memory
141 The physical limit is reported as
142 .Va vm.memguard.phys_limit
143 and the virtual space reserved for
146 .Va vm.memguard.mapsize .
149 will not do page promotions for any allocation smaller than
150 .Va vm.memguard.minsize
152 The default is 0, meaning all allocations can potentially be guarded.
154 can guard sufficiently large allocations randomly, with average
155 frequency of every one in 100000 /
156 .Va vm.memguard.frequency
158 The default is 0, meaning no allocations are randomly guarded.
161 can optionally add unmapped guard pages around each allocation to
162 detect overflow and underflow, if
163 .Va vm.memguard.options
165 This option is enabled by default.
167 will optionally guard all allocations of
170 .Va vm.memguard.options
172 This option is off by default.
177 zones that have been initialized with the
179 flag set, since it can produce false positives on them.
180 However, this safety measure can be turned off by setting bit 3
182 .Va vm.memguard.options
198 was originally written by
199 .An Bosko Milekic Aq Mt bmilekic@FreeBSD.org .
200 This manual page was originally written by
201 .An Christian Brueffer Aq Mt brueffer@FreeBSD.org .
202 Additions have been made by
203 .An Matthew Fleming Aq Mt mdf@FreeBSD.org
205 .An Gleb Smirnoff Aq Mt glebius@FreeBSD.org
206 to both the implementation and the documentation.