linux-kernel - Re: [PATCH 4/4] asm-generic/bitsperlong.h: Add sanity checks for __BITS_PER

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1a77fda4-3cf6-4c19-aa36-b5f0e305b313@zytor.com>
Date: Mon, 19 Jan 2026 07:33:13 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        Andreas Larsson <andreas@...sler.com>,
        Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>
Cc: sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 4/4] asm-generic/bitsperlong.h: Add sanity checks for
 __BITS_PER_LONG

On 2026-01-15 23:40, Thomas Weißschuh wrote:
> The value of __BITS_PER_LONG from architecture-specific logic should
> always match the generic one if that is available. It should also match
> the actual C type 'long'.
> 
> Mismatches can happen for example when building the compat vDSO. Either
> during the compilation, see commit 9a6d3ff10f7f ("arm64: uapi: Provide
> correct __BITS_PER_LONG for the compat vDSO"), or when running sparse
> when mismatched CHECKFLAGS are inherited from the kernel build.
> 
> Add some consistency checks which detect such issues early and clearly.
> The tests are added to the UAPI header to make sure it is also used when
> building the vDSO as that is not supposed to use regular kernel headers.
> 
> The kernel-interal BITS_PER_LONG is not checked as it is derived from
> CONFIG_64BIT and therefore breaks for the compat vDSO. See the similar,
> deactivated check in include/asm-generic/bitsperlong.h.
> 
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> ---
>  include/uapi/asm-generic/bitsperlong.h | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/include/uapi/asm-generic/bitsperlong.h b/include/uapi/asm-generic/bitsperlong.h
> index fadb3f857f28..9d762097ae0c 100644
> --- a/include/uapi/asm-generic/bitsperlong.h
> +++ b/include/uapi/asm-generic/bitsperlong.h
> @@ -28,4 +28,18 @@
>  #define __BITS_PER_LONG_LONG 64
>  #endif
>  
> +/* Consistency checks */
> +#ifdef __KERNEL__
> +#if defined(__CHAR_BIT__) && defined(__SIZEOF_LONG__)
> +#if __BITS_PER_LONG != (__CHAR_BIT__ * __SIZEOF_LONG__)
> +#error Inconsistent word size. Check uapi/asm/bitsperlong.h
> +#endif
> +#endif
> +
> +#ifndef __ASSEMBLER__
> +_Static_assert(sizeof(long) * 8 == __BITS_PER_LONG,
> +	       "Inconsistent word size. Check uapi/asm/bitsperlong.h");
> +#endif
> +#endif /* __KERNEL__ */
> +
>  #endif /* _UAPI__ASM_GENERIC_BITS_PER_LONG */
> 

Do we actually support any compilers which *don't* define __SIZEOF_LONG__?

	-hpa