linux-kernel - Re: [PATCH] unwind deferred: Annotate struct unwind_cache with __counted

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Message-ID: <20251114084346.6469edc0@gandalf.local.home>
Date: Fri, 14 Nov 2025 08:43:46 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, Kees Cook <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] unwind deferred: Annotate struct unwind_cache with
 __counted_by

On Fri, 14 Nov 2025 13:27:47 +0100
Thorsten Blum <thorsten.blum@...ux.dev> wrote:

> Add the __counted_by() compiler attribute to the flexible array member
> 'entries' to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
> ---
>  include/linux/unwind_deferred_types.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/unwind_deferred_types.h b/include/linux/unwind_deferred_types.h
> index 33b62ac25c86..d4b67f0116f3 100644
> --- a/include/linux/unwind_deferred_types.h
> +++ b/include/linux/unwind_deferred_types.h
> @@ -5,7 +5,7 @@
>  struct unwind_cache {
>  	unsigned long		unwind_completed;
>  	unsigned int		nr_entries;
> -	unsigned long		entries[];
> +	unsigned long		entries[] __counted_by(nr_entries);
>  };
>  
>  /*

Wrong!

I need to add a comment here that entries is not bound by nr_entries.

   https://lore.kernel.org/all/20250730093249.4833be14@gandalf.local.home/

Maybe this?:

diff --git a/include/linux/unwind_deferred_types.h b/include/linux/unwind_deferred_types.h
index 33b62ac25c86..d05409bb14fa 100644
--- a/include/linux/unwind_deferred_types.h
+++ b/include/linux/unwind_deferred_types.h
@@ -5,7 +5,7 @@
 struct unwind_cache {
 	unsigned long		unwind_completed;
 	unsigned int		nr_entries;
-	unsigned long		entries[];
+	unsigned long		entries[]; /* Fixed size, not bound by nr_entries */
 };
 
 /*



-- Steve