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Helge Deller 9aa326a6f2 lib/clz_ctz.c: Fix __clzdi2() and __ctzdi2() for 32-bit kernels 
commit 382d4cd184 upstream.

The gcc compiler translates on some architectures the 64-bit
__builtin_clzll() function to a call to the libgcc function __clzdi2(),
which should take a 64-bit parameter on 32- and 64-bit platforms.

But in the current kernel code, the built-in __clzdi2() function is
defined to operate (wrongly) on 32-bit parameters if BITS_PER_LONG ==
32, thus the return values on 32-bit kernels are in the range from
[0..31] instead of the expected [0..63] range.

This patch fixes the in-kernel functions __clzdi2() and __ctzdi2() to
take a 64-bit parameter on 32-bit kernels as well, thus it makes the
functions identical for 32- and 64-bit kernels.

This bug went unnoticed since kernel 3.11 for over 10 years, and here
are some possible reasons for that:

 a) Some architectures have assembly instructions to count the bits and
    which are used instead of calling __clzdi2(), e.g. on x86 the bsr
    instruction and on ppc cntlz is used. On such architectures the
    wrong __clzdi2() implementation isn't used and as such the bug has
    no effect and won't be noticed.

 b) Some architectures link to libgcc.a, and the in-kernel weak
    functions get replaced by the correct 64-bit variants from libgcc.a.

 c) __builtin_clzll() and __clzdi2() doesn't seem to be used in many
    places in the kernel, and most likely only in uncritical functions,
    e.g. when printing hex values via seq_put_hex_ll(). The wrong return
    value will still print the correct number, but just in a wrong
    formatting (e.g. with too many leading zeroes).

 d) 32-bit kernels aren't used that much any longer, so they are less
    tested.

A trivial testcase to verify if the currently running 32-bit kernel is
affected by the bug is to look at the output of /proc/self/maps:

Here the kernel uses a correct implementation of __clzdi2():

  root@debian:~# cat /proc/self/maps
  00010000-00019000 r-xp 00000000 08:05 787324     /usr/bin/cat
  00019000-0001a000 rwxp 00009000 08:05 787324     /usr/bin/cat
  0001a000-0003b000 rwxp 00000000 00:00 0          [heap]
  f7551000-f770d000 r-xp 00000000 08:05 794765     /usr/lib/hppa-linux-gnu/libc.so.6
  ...

and this kernel uses the broken implementation of __clzdi2():

  root@debian:~# cat /proc/self/maps
  0000000010000-0000000019000 r-xp 00000000 000000008:000000005 787324  /usr/bin/cat
  0000000019000-000000001a000 rwxp 000000009000 000000008:000000005 787324  /usr/bin/cat
  000000001a000-000000003b000 rwxp 00000000 00:00 0  [heap]
  00000000f73d1000-00000000f758d000 r-xp 00000000 000000008:000000005 794765  /usr/lib/hppa-linux-gnu/libc.so.6
  ...

Signed-off-by: Helge Deller <deller@gmx.de>
Fixes: 4df87bb7b6 ("lib: add weak clz/ctz functions")
Cc: Chanho Min <chanho.min@lge.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: stable@vger.kernel.org # v3.11+
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-08-30 16:35:15 +02:00
arch MIPS: dec: prom: Address -Warray-bounds warning 2023-08-30 16:35:10 +02:00
block block: bio-integrity: Copy flags when bio_integrity_payload is cloned 2023-03-11 16:26:35 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-25 11:46:44 +02:00
crypto verify_pefile: relax wrapper length check 2023-04-20 12:02:12 +02:00
Documentation Documentation: security-bugs.rst: update preferences when dealing with the linux-distros group 2023-08-11 11:33:53 +02:00
drivers ibmveth: Use dcbf rather than dcbfl 2023-08-30 16:35:14 +02:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:20:30 +01:00
fs cifs: Release folio lock on fscache read hit. 2023-08-30 16:35:13 +02:00
include sock: annotate data-races around prot->memory_pressure 2023-08-30 16:35:14 +02:00
init init, x86: Move mem_encrypt_init() into arch_cpu_finalize_init() 2023-08-08 19:48:24 +02:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:16:33 +01:00
kernel tracing: Fix memleak due to race between current_tracer and trace 2023-08-30 16:35:14 +02:00
lib lib/clz_ctz.c: Fix __clzdi2() and __ctzdi2() for 32-bit kernels 2023-08-30 16:35:15 +02:00
mm treewide: Remove uninitialized_var() usage 2023-08-11 11:33:32 +02:00
net batman-adv: Fix batadv_v_ogm_aggr_send memory leak 2023-08-30 16:35:15 +02:00
samples samples/kretprobes: Fix return value if register_kretprobe() failed 2021-11-26 11:40:31 +01:00
scripts modpost: fix off by one in is_executable_section() 2023-08-11 11:33:38 +02:00
security integrity: Fix possible multiple allocation in integrity_inode_get() 2023-08-11 11:33:41 +02:00
sound ASoC: rt5665: add missed regulator_bulk_disable 2023-08-30 16:35:13 +02:00
tools radix tree test suite: fix incorrect allocation size for pthreads 2023-08-16 18:10:53 +02:00
usr initramfs: restore default compression behavior 2020-04-13 10:34:19 +02:00
virt KVM: arm64: vgic: Fix exit condition in scan_its_table() 2022-11-03 23:50:50 +09:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS Remove DECnet support from kernel 2023-06-21 15:38:58 +02:00
Makefile Linux 4.14.323 2023-08-16 18:10:55 +02:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

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

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

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.