From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D64A411C83 for ; Mon, 28 Aug 2023 10:29:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 59C88C433C7; Mon, 28 Aug 2023 10:29:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1693218576; bh=oFMK5b4TU7N8HPqFhdanzjmLjgvvgseS/+9OwS6g5eM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RkedwjkeIdGMbjdwS7wjL0BZsdVQmAiXjsZpA29x15DZfDLI/EfPzym/8vu2ZLh06 Mb5jnenmr/WLnkBEWwNuUQy47O+p8HmVN31RwWKYbQu6M4/KlH++N6F0cbob8Z8/+D 2QiMzv20pOjR6CxrEP0eyYh2pJ5qF0qZuPP+2xdI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Helge Deller , Chanho Min , Geert Uytterhoeven , Linus Torvalds Subject: [PATCH 4.19 117/129] lib/clz_ctz.c: Fix __clzdi2() and __ctzdi2() for 32-bit kernels Date: Mon, 28 Aug 2023 12:13:31 +0200 Message-ID: <20230828101157.506132241@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20230828101153.030066927@linuxfoundation.org> References: <20230828101153.030066927@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 4.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Helge Deller commit 382d4cd1847517ffcb1800fd462b625db7b2ebea 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 Fixes: 4df87bb7b6a22 ("lib: add weak clz/ctz functions") Cc: Chanho Min Cc: Geert Uytterhoeven Cc: stable@vger.kernel.org # v3.11+ Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- lib/clz_ctz.c | 32 ++++++-------------------------- 1 file changed, 6 insertions(+), 26 deletions(-) --- a/lib/clz_ctz.c +++ b/lib/clz_ctz.c @@ -30,36 +30,16 @@ int __weak __clzsi2(int val) } EXPORT_SYMBOL(__clzsi2); -int __weak __clzdi2(long val); -int __weak __ctzdi2(long val); -#if BITS_PER_LONG == 32 - -int __weak __clzdi2(long val) +int __weak __clzdi2(u64 val); +int __weak __clzdi2(u64 val) { - return 32 - fls((int)val); + return 64 - fls64(val); } EXPORT_SYMBOL(__clzdi2); -int __weak __ctzdi2(long val) +int __weak __ctzdi2(u64 val); +int __weak __ctzdi2(u64 val) { - return __ffs((u32)val); + return __ffs64(val); } EXPORT_SYMBOL(__ctzdi2); - -#elif BITS_PER_LONG == 64 - -int __weak __clzdi2(long val) -{ - return 64 - fls64((u64)val); -} -EXPORT_SYMBOL(__clzdi2); - -int __weak __ctzdi2(long val) -{ - return __ffs64((u64)val); -} -EXPORT_SYMBOL(__ctzdi2); - -#else -#error BITS_PER_LONG not 32 or 64 -#endif