e3813573bd
use-after-free over a longer time. Also release the backing pages of a guarded allocation at free(9) time to reduce the overhead of using memguard(9). Allow setting and varying the malloc type at run-time. Add knobs to allow: - randomly guarding memory - adding un-backed KVA guard pages to detect underflow and overflow - a lower limit on the size of allocations that are guarded Reviewed by: alc Reviewed by: brueffer, Ulrich Spörlein <uqs spoerlein net> (man page) Silence from: -arch Approved by: zml (mentor) MFC after: 1 month
169 lines
4.6 KiB
Groff
169 lines
4.6 KiB
Groff
.\" Copyright (c) 2005 Christian Brueffer
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 2, 2010
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.Dt MEMGUARD 9
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.Os
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.Sh NAME
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.Nm MemGuard
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.Nd "memory allocator for debugging purposes"
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.Sh SYNOPSIS
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.Cd "options DEBUG_MEMGUARD"
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.Sh DESCRIPTION
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.Nm
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is a simple and small replacement memory allocator designed
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to help detect tamper-after-free scenarios.
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These problems are more and more common and likely with
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multithreaded kernels where race conditions are more prevalent.
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.Pp
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Currently,
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.Nm
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can take over
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.Fn malloc ,
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.Fn realloc
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and
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.Fn free
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for a single malloc type.
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.Nm
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can also guard all allocations larger than
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.Dv PAGE_SIZE ,
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and can guard a random fraction of all allocations.
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There is also a knob to prevent allocations smaller than a specified
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size from being guarded, to limit memory waste.
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.Sh EXAMPLES
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To use
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.Nm
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for a memory type, either add an entry to
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.Pa /boot/loader.conf :
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.Bd -literal -offset indent
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vm.memguard.desc=<memory_type>
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.Ed
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.Pp
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Or set the
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.Va vm.memguard.desc
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.Xr sysctl 8
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variable at run-time:
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.Bd -literal -offset indent
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sysctl vm.memguard.desc=<memory_type>
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.Ed
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.Pp
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Where
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.Ar memory_type
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is a short description of the memory type to monitor.
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Only allocations from that
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.Ar memory_type
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made after
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.Va vm.memguard.desc
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is set will potentially be guarded.
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If
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.Va vm.memguard.desc
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is modified at run-time then only allocations of the new
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.Ar memory_type
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will potentially be guarded once the
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.Xr sysctl 8
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is set.
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Existing guarded allocations will still be properly released by
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.Xr free 9 .
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.Pp
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The short description of a
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.Xr malloc 9
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type is the second argument to
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.Xr MALLOC_DEFINE 9 ,
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so one has to find it in the kernel source.
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.Pp
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The
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.Va vm.memguard.divisor
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boot-time tunable is used to scale how much of the system's physical
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memory
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.Nm
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is allowed to consume.
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The default is 10, so up to
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.Va cnt.v_page_count Ns /10
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pages can be used.
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.Nm
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will reserve
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.Va vm_kmem_max
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/
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.Va vm.memguard.divisor
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bytes of virtual address space, limited by twice the physical memory
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size.
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The physical limit is reported as
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.Va vm.memguard.phys_limit
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and the virtual space reserved for
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.Nm
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is reported as
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.Va vm.memguard.mapsize .
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.Pp
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.Nm
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will not do page promotions for any allocation smaller than
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.Va vm.memguard.minsize
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bytes.
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The default is 0, meaning all allocations can potentially be guarded.
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.Nm
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can guard sufficiently large allocations randomly, with average
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frequency of every one in 100000 /
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.Va vm.memguard.frequency
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allocations.
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The default is 0, meaning no allocations are randomly guarded.
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.Pp
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.Nm
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can optionally add unmapped guard pages around each allocation to
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detect overflow and underflow, if
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.Va vm.memguard.options
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has the 1 bit set.
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This option is enabled by default.
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.Nm
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will optionally guard all allocations of
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.Dv PAGE_SIZE
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or larger if
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.Va vm.memguard.options
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has the 2 bit set.
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This option is off by default.
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.Sh SEE ALSO
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.Xr sysctl 8 ,
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.Xr vmstat 8 ,
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.Xr contigmalloc 9 ,
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.Xr malloc 9 ,
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.Xr redzone 9
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.Sh HISTORY
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.Nm
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first appeared in
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.Fx 6.0 .
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.Sh AUTHORS
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.An -nosplit
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.Nm
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was originally written by
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.An Bosko Milekic Aq bmilekic@FreeBSD.org .
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This manual page was originally written by
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.An Christian Brueffer Aq brueffer@FreeBSD.org .
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Additions have been made by
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.An Matthew Fleming Aq mdf@FreeBSD.org
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to both the implementation and the documentation.
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.Sh BUGS
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Currently, it is not possible to override UMA
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.Xr zone 9
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allocations.
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