Linux kernel modifications for the Kernel Hacking exam
ec4288fe63
Users can specify the hugetlb page size in the mmap, shmget and
memfd_create system calls. This is done by using 6 bits within the flags
argument to encode the base-2 logarithm of the desired page size. The
routine hstate_sizelog() uses the log2 value to find the corresponding
hugetlb hstate structure. Converting the log2 value (page_size_log) to
potential hugetlb page size is the simple statement:
1UL << page_size_log
Because only 6 bits are used for page_size_log, the left shift can not be
greater than 63. This is fine on 64 bit architectures where a long is 64
bits. However, if a value greater than 31 is passed on a 32 bit
architecture (where long is 32 bits) the shift will result in undefined
behavior. This was generally not an issue as the result of the undefined
shift had to exactly match hugetlb page size to proceed.
Recent improvements in runtime checking have resulted in this undefined
behavior throwing errors such as reported below.
Fix by comparing page_size_log to BITS_PER_LONG before doing shift.
Link: https://lkml.kernel.org/r/20230216013542.138708-1-mike.kravetz@oracle.com
Link: https://lore.kernel.org/lkml/CA+G9fYuei_Tr-vN9GS7SfFyU1y9hNysnf=PB7kT0=yv4MiPgVg@mail.gmail.com/
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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.