6c635129bf
commit b5fab345654c603c07525100d744498f28786929 upstream.
In lock_region, simplify the calculation of the region_width parameter.
This field is the size, but encoded as ceil(log2(size)) - 1.
ceil(log2(size)) may be computed directly as fls(size - 1). However, we
want to use the 64-bit versions as the amount to lock can exceed
32-bits.
This avoids undefined (and completely wrong) behaviour when locking all
memory (size ~0). In this case, the old code would "round up" ~0 to the
nearest page, overflowing to 0. Since fls(0) == 0, this would calculate
a region width of 10 + 0 = 10. But then the code would shift by
(region_width - 11) = -1. As shifting by a negative number is undefined,
UBSAN flags the bug. Of course, even if it were defined the behaviour is
wrong, instead of locking all memory almost none would get locked.
The new form of the calculation corrects this special case and avoids
the undefined behaviour.
Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reported-and-tested-by: Chris Morgan <macromorgan@hotmail.com>
Fixes:
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Documentation | ||
LICENSES | ||
arch | ||
block | ||
certs | ||
crypto | ||
drivers | ||
fs | ||
include | ||
init | ||
ipc | ||
kernel | ||
lib | ||
mm | ||
net | ||
samples | ||
scripts | ||
security | ||
sound | ||
tools | ||
usr | ||
virt | ||
.clang-format | ||
.cocciconfig | ||
.get_maintainer.ignore | ||
.gitattributes | ||
.gitignore | ||
.mailmap | ||
COPYING | ||
CREDITS | ||
Kbuild | ||
Kconfig | ||
MAINTAINERS | ||
Makefile | ||
README |
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.