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Filename Latest commit message Latest commit date
Nicholas Piggin b65458b6be powerpc/64s: flush L1D on kernel entry
commit f79643787e0a0762d2409b7b8334e83f22d85695 upstream.

[backporting note: we need to mark some exception handlers as out-of-line
 because the flushing makes them take too much space -- dja]

IBM Power9 processors can speculatively operate on data in the L1 cache
before it has been completely validated, via a way-prediction mechanism. It
is not possible for an attacker to determine the contents of impermissible
memory using this method, since these systems implement a combination of
hardware and software security measures to prevent scenarios where
protected data could be leaked.

However these measures don't address the scenario where an attacker induces
the operating system to speculatively execute instructions using data that
the attacker controls. This can be used for example to speculatively bypass
"kernel user access prevention" techniques, as discovered by Anthony
Steinhauser of Google's Safeside Project. This is not an attack by itself,
but there is a possibility it could be used in conjunction with
side-channels or other weaknesses in the privileged code to construct an
attack.

This issue can be mitigated by flushing the L1 cache between privilege
boundaries of concern. This patch flushes the L1 cache on kernel entry.

This is part of the fix for CVE-2020-4788.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-11-22 10:14:10 +01:00
arch powerpc/64s: flush L1D on kernel entry 2020-11-22 10:14:10 +01:00
block
certs
crypto
Documentation powerpc/64s: flush L1D on kernel entry 2020-11-22 10:14:10 +01:00
drivers drm/i915: Correctly set SFC capability for video engines 2020-11-18 19:20:33 +01:00
fs Convert trailing spaces and periods in path components 2020-11-18 19:20:34 +01:00
include
init
ipc
kernel perf/core: Fix race in the perf_mmap_close() function 2020-11-18 19:20:33 +01:00
lib
LICENSES
mm
net net: sch_generic: fix the missing new qdisc assignment bug 2020-11-18 19:20:33 +01:00
samples
scripts
security
sound
tools selftests/powerpc: rfi_flush: disable entry flush if present 2020-11-22 10:14:10 +01:00
usr
virt
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
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Makefile Linux 5.4.78 2020-11-18 19:20:34 +01:00
README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.