5efe338f3d
Suppose that userspace is executing with the non-standard segment descriptors. Then, until exception or interrupt handler executed SET_KERNEL_SEGS, kernel is still executing with user %ds, %es and %fs. If an interrupt occurs in this window, the interrupt handler is executed unsafely, relying on usability of the usermode registers. If the interrupt results in the context switch on return, the contamination of the kernel state spreads to the thread we switched to. As result, kernel data accesses might fault or, if only the base is changed, completely messed up. More, if the user segment was allocated in LDT, another thread might mark the descriptor as invalid before doreti code tried to reload them. In this case kernel panics. The issue exists for all exception entry points which use trap gate, and thus do not automatically disable interrupts on entry, and for lcall_handler. Fix is two-fold: first, we need to disable interrupts for all kernel entries, changing the IDT descriptor types from trap gate to interrupt gate. Interrupts are re-enabled not earlier than the kernel segments are loaded into the segment registers. Second, we only load the segment registers from the trap frame when returning to usermode. For the later, all interrupt return paths must happen through the doreti common code. There is no way to disable interrupts on call gate, which is the supposed mode of servicing for lcall $7,$0 syscalls. Change the LDT descriptor 0 into a code segment type and point it to the userspace trampoline which redirects the syscall to int $0x80. All the measures make the segment register handling similar to that of amd64. We do not apply amd64 optimizations of not reloading segment registers on return from the syscall. Reported by: Maxime Villard <max@m00nbsd.net> Tested by: pho (the non-lcall part) Reviewed by: jhb Sponsored by: The FreeBSD Foundation MFC after: 2 weeks Differential revision: https://reviews.freebsd.org/D12402 |
||
|---|---|---|
| bin | ||
| cddl | ||
| contrib | ||
| crypto | ||
| etc | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
| sbin | ||
| secure | ||
| share | ||
| sys | ||
| targets | ||
| tests | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| .arcconfig | ||
| .arclint | ||
| COPYRIGHT | ||
| LOCKS | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.inc1 | ||
| Makefile.libcompat | ||
| ObsoleteFiles.inc | ||
| README | ||
| README.md | ||
| UPDATING | ||
FreeBSD Source:
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. See build(7) and 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. See build(7), config(8), and http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html for more information.
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 kernel configuration files reside in the sys/<arch>/conf
sub-directory. GENERIC is the default configuration used in release builds.
NOTES contains entries and documentation for all possible
devices, not just those commonly used.
Source Roadmap:
bin System/user commands.
cddl Various commands and libraries under the Common Development
and Distribution License.
contrib Packages contributed by 3rd parties.
crypto Cryptography stuff (see crypto/README).
etc Template files for /etc.
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.
tests Regression tests which can be run by Kyua. See tests/README
for additional information.
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