Date: Thu, 22 Jul 2010 20:41:20 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: mdf@freebsd.org Cc: freebsd-arch@freebsd.org Subject: Re: Multi-zone malloc(9) Message-ID: <20100722174120.GR2381@deviant.kiev.zoral.com.ua> In-Reply-To: <AANLkTikoY8CuAF3DThBAXH_mu1QAuUWyRMtkaIomaoi7@mail.gmail.com> References: <AANLkTikoY8CuAF3DThBAXH_mu1QAuUWyRMtkaIomaoi7@mail.gmail.com>
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--ngluH3DisTFy0Cjl Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jul 22, 2010 at 09:54:51AM -0700, mdf@freebsd.org wrote: > Occasionally we run into use-after-free and malloc'd buffer overrun > scenarios. When this happens it can be rather difficult to determine > what code is at fault, since e.g. every 64 byte allocation, regardless > of malloc type, comes from the same UMA zone. This means that an > overflow in M_TEMP will affect M_DEVBUF, etc. Adding multiple uma > zones for each bucket size means that we can hash on the malloc type's > shortdesc field so that there are fewer collisions and misused memory > from one malloc type only affects a subset of other malloc types. > Varying the hash means that, with several crashes due to memory stomp, > a single malloc type can usually be determined as the culprit. If the > bug isn't obvious from inspection at this point, MemGuard will help > catch the offender. >=20 > The patch at: >=20 > http://people.freebsd.org/~mdf/multizone_malloc.patch >=20 > implements an optional multi-zone malloc(9). By default there is a > single zone, and MALLOC_DEBUG_MAXZONES can be specified in the kernel > configuration file. A ddb function will print all the malloc types > that have a hash collision with the specified type. >=20 > A few questions for -arch@: >=20 > - We found this very useful at Isilon. Should this go into CURRENT? >=20 > - Should this be on by default for GENERIC? The memory overhead of 8 > uma zones per malloc allocation size shouldn't be very large. >=20 > - would a __FreeBSD_version bump be needed since the malloc_internal > type is known by user-space? Can you quantify the overhead, both in CPU time and memory usage terms ? I would much prefer to have debug and non-debug kernels to run similar code, in other words, can the multizone allocation be enabled unconditionally ? --ngluH3DisTFy0Cjl Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (FreeBSD) iEUEARECAAYFAkxIgr8ACgkQC3+MBN1Mb4j2cwCfSRtigwr3xkLvmJ0eAbh4ho2y +70Al1bwaSE6Q4RtO+BaHj0hT6X8oRc= =mVa3 -----END PGP SIGNATURE----- --ngluH3DisTFy0Cjl--
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