Re: [PATCH 1/2] stacktrace: Add __counted_by_ptr attribute to struct stack_trace

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 8/23/26 06:35, Bill Wendling wrote:
> For hardening and catching out-of-bounds accesses to the 'entries'
> pointer field in 'struct stack_trace', associate it with its count
> field 'max_entries' using the __counted_by_ptr attribute.
> 
> An analysis of the codebase reveals that 'struct stack_trace' is
> instantiated and initialized across several entry points in
> 'kernel/stacktrace.c'. In each execution path, 'trace.entries' is
> assigned a buffer of size 'size', and 'trace.max_entries' is assigned
> 'size' concurrently within the structure's initializer block. The
> pointer is not accessed before the count is set.
> 
> Because 'trace.entries' is always assigned at the same time as
> 'trace.max_entries' during initialization and is never reallocated
> or accessed beforehand, there are no uninitialized access windows.
> The 'max_entries' field accurately holds the exact element count
> of the buffer allocated for the 'entries' pointer, ensuring that
> compiler fortification and KASAN bounds checks using __counted_by_ptr
> do not trigger false-positive bounds checks or runtime panics.
> 
> Assisted-by: Gemini Next
> Signed-off-by: Bill Wendling <morbo@google.com>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks
-Gustavo

> ---
> Cc: Kees Cook <kees@kernel.org>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Brendan Higgins <brendan.higgins@linux.dev>
> Cc: David Gow <david@davidgow.net>
> Cc: Rae Moar <raemoar63@gmail.com>
> Cc: Ryota Sakamoto <sakamo.ryota@gmail.com>
> Cc: Kuan-Wei Chiu <visitorckw@gmail.com>
> Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
> Cc: Dmitry Antipov <dmantipov@yandex.ru>
> Cc: Petr Mladek <pmladek@suse.com>
> Cc: Kir Chou <note351@hotmail.com>
> Cc: codemender-patching+linux@google.com
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-hardening@vger.kernel.org
> Cc: linux-kselftest@vger.kernel.org
> Cc: kunit-dev@googlegroups.com
> Cc: linux-hardening@vger.kernel.org
> ---
>   include/linux/stacktrace.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/stacktrace.h b/include/linux/stacktrace.h
> index 97455880ac41..fbb0925d8864 100644
> --- a/include/linux/stacktrace.h
> +++ b/include/linux/stacktrace.h
> @@ -81,7 +81,7 @@ unsigned int filter_irq_stacks(unsigned long *entries, unsigned int nr_entries);
>   /* Internal interfaces. Do not use in generic code */
>   struct stack_trace {
>   	unsigned int nr_entries, max_entries;
> -	unsigned long *entries;
> +	unsigned long *entries __counted_by_ptr(max_entries);
>   	unsigned int skip;	/* input argument: How many entries to skip */
>   };
>