freebsd kernel with SKQ
b21a1da537
The RAS implementation would set the end address, then the start address. These were used by the kernel to restart a RAS sequence if it was interrupted. When the thread switching code ran, it would check these values and adjust the PC and clear them if it did. However, there's a small flaw in this scheme. Thread T1, sets the end address and gets preempted. Thread T2 runs and also does a RAS operation. This resets end to zero. Thread T1 now runs again and sets start and then begins the RAS sequence, but is preempted before the RAS sequence executes its last instruction. The kernel code that would ordinarily restart the RAS sequence doesn't because the PC isn't between start and 0, so the PC isn't set to the start of the sequence. So when T1 is resumed again, it is at the wrong location for RAS to produce the correct results. This causes the wrong results for the atomic sequence. The window for the first race is 3 instructions. The window for the second race is 5-10 instructions depending on the atomic operation. This makes this failure fairly rare and hard to reproduce. Mutexs are implemented in libthr using atomic operations. When the above race would occur, a lock could get stuck locked, causing many downstream problems, as you might expect. Also, make sure to reset the start and end address when doing a syscall, or a malicious process could set them before doing a syscall. Reviewed by: imp, ups (thanks guys) Pointy hat to: cognet MFC After: 3 days |
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| compat/opensolaris | ||
| contrib | ||
| crypto | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
| sbin | ||
| secure | ||
| share | ||
| sys | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| COPYRIGHT | ||
| LOCKS | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.inc1 | ||
| ObsoleteFiles.inc | ||
| README | ||
| UPDATING | ||
This is the top level of the FreeBSD source directory. This file was last revised on: $FreeBSD$ For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information). The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree, the most commonly used one being ``world'', which rebuilds and installs everything in the FreeBSD system from the source tree except the kernel, the kernel-modules and the contents of /etc. The ``world'' target should only be used in cases where the source tree has not changed from the currently running version. See: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html for more information, including setting make(1) variables. The ``buildkernel'' and ``installkernel'' targets build and install the kernel and the modules (see below). Please see the top of the Makefile in this directory for more information on the standard build targets and compile-time flags. Building a kernel is a somewhat more involved process, documentation for which can be found at: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html And in the config(8) man page. Note: If you want to build and install the kernel with the ``buildkernel'' and ``installkernel'' targets, you might need to build world before. More information is available in the handbook. The sample kernel configuration files reside in the sys/<arch>/conf sub-directory (assuming that you've installed the kernel sources), the file named GENERIC being the one used to build your initial installation kernel. The file NOTES contains entries and documentation for all possible devices, not just those commonly used. It is the successor of the ancient LINT file, but in contrast to LINT, it is not buildable as a kernel but a pure reference and documentation file. Source Roadmap: --------------- bin System/user commands. contrib Packages contributed by 3rd parties. crypto Cryptography stuff (see crypto/README). etc Template files for /etc. games Amusements. gnu Various commands and libraries under the GNU Public License. Please see gnu/COPYING* for more information. include System include files. kerberos5 Kerberos5 (Heimdal) package. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. rescue Build system for statically linked /rescue utilities. sbin System commands. secure Cryptographic libraries and commands. share Shared resources. sys Kernel sources. tools Utilities for regression testing and miscellaneous tasks. usr.bin User commands. usr.sbin System administration commands. For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/synching.html