linux-kernel - Re: [PATCH 1/2] Compiler Attributes: Add __counted_by

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: <CAGG=3QXOTNaYJMNVB_6p4OF58=u5GFgZ05FAwOLRWGfuqLo_2Q@mail.gmail.com>
Date: Fri, 21 Nov 2025 11:46:23 -0800
From: Bill Wendling <morbo@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: Kees Cook <kees@...nel.org>, "Gustavo A. R. Silva" <gustavoars@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
	Justin Stitt <justinstitt@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Heiko Carstens <hca@...ux.ibm.com>, Marc Herbert <Marc.Herbert@...ux.intel.com>, 
	Uros Bizjak <ubizjak@...il.com>, Tejun Heo <tj@...nel.org>, Jeff Xu <jeffxu@...omium.org>, 
	Michal Koutný <mkoutny@...e.com>, 
	Shakeel Butt <shakeel.butt@...ux.dev>, 
	Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
	John Stultz <jstultz@...gle.com>, Christian Brauner <brauner@...nel.org>, 
	Randy Dunlap <rdunlap@...radead.org>, Brian Gerst <brgerst@...il.com>, 
	Masahiro Yamada <masahiroy@...nel.org>, linux-hardening@...r.kernel.org, 
	llvm@...ts.linux.dev, Jan Hendrik Farr <kernel@...rr.cc>, Qing Zhao <qing.zhao@...cle.com>
Subject: Re: [PATCH 1/2] Compiler Attributes: Add __counted_by_ptr macro

On Fri, Nov 21, 2025 at 11:40 AM Bill Wendling <morbo@...gle.com> wrote:
>
> Clang and GCC are expanding the '__counted_by' attribute to support
> pointers in structs. Clang has support for it since version 21. This
> requires defining a separate macro, '__counted_by_ptr', because, while
> the attribute has the same name for both a pointer and a flexible array
> member, minimal compiler versions need to catch up.
>
> The effect of this feature is the same as for __counted_by on flexible
> array members. It provides hardening the ability to perform run-time
> bounds checking on otherwise unknown-size pointers.
>
> Cc: Kees Cook <kees@...nel.org>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: Nathan Chancellor <nathan@...nel.org>
> Cc: Nick Desaulniers <nick.desaulniers+lkml@...il.com>
> Cc: Justin Stitt <justinstitt@...gle.com>
> Cc: Miguel Ojeda <ojeda@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Heiko Carstens <hca@...ux.ibm.com>
> Cc: Marc Herbert <Marc.Herbert@...ux.intel.com>
> Cc: Uros Bizjak <ubizjak@...il.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Jeff Xu <jeffxu@...omium.org>
> Cc: "Michal Koutný" <mkoutny@...e.com>
> Cc: Shakeel Butt <shakeel.butt@...ux.dev>
> Cc: "Thomas Weißschuh" <thomas.weissschuh@...utronix.de>
> Cc: John Stultz <jstultz@...gle.com>
> Cc: Christian Brauner <brauner@...nel.org>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Cc: Brian Gerst <brgerst@...il.com>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-hardening@...r.kernel.org
> Cc: llvm@...ts.linux.dev
> Signed-off-by: Bill Wendling <morbo@...gle.com>
> ---
>  include/linux/compiler_types.h | 11 +++++++++++
>  init/Kconfig                   |  5 +++++
>  2 files changed, 16 insertions(+)
>
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 0a1b9598940d..2b0251bb951c 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -351,6 +351,17 @@ struct ftrace_likely_data {
>  # define __assume(expr)
>  #endif
>
> +/*
> + * Optional: only supported since clang >= 21
> + *
> + * clang: https://github.com/llvm/llvm-project/pull/137250
> + */
> +#ifdef CONFIG_CC_HAS_COUNTED_BY_FOR_POINTER
> +#define __counted_by_ptr(member)       __attribute__((__counted_by__(member)))
> +#else
> +#define __counted_by_ptr(member)
> +#endif
> +
>  /*
>   * Optional: only supported since gcc >= 15
>   * Optional: only supported since clang >= 18
> diff --git a/init/Kconfig b/init/Kconfig
> index cab3ad28ca49..298c94c4c1b1 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -139,6 +139,11 @@ config CC_HAS_COUNTED_BY
>         # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
>         default y if CC_IS_GCC && GCC_VERSION >= 150100
>
> +config CC_HAS_COUNTED_BY_ON_POINTERS
> +       bool
> +       # Needs clang 21.1.0 or higher.
> +       default y if CC_IS_CLANG && CLANG_VERSION >= 210100
> +
I mistakenly left out GCC from here. I'll roll that in with v2.

-bw

>  config CC_HAS_MULTIDIMENSIONAL_NONSTRING
>         def_bool $(success,echo 'char tag[][4] __attribute__((__nonstring__)) = { };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror)
>
> --
> 2.52.0.rc2.455.g230fcf2819-goog
>