[PATCH] sched/task_stack: Add missing const qualifier to end_of_stack()

[PATCH] sched/task_stack: Add missing const qualifier to end_of_stack()

[Kees Cook]

Add missing const qualifier to the non-CONFIG_THREAD_INFO_IN_TASK
version of end_of_stack() to match the CONFIG_THREAD_INFO_IN_TASK
version. Fixes a warning with CONFIG_KSTACK_ERASE=y on archs that don't
select THREAD_INFO_IN_TASK (such as LoongArch):

  error: passing 'const struct task_struct *' to parameter of type 'struct task_struct *' discards qualifiers

The stackleak_task_low_bound() function correctly uses a const task
parameter, but the legacy end_of_stack() prototype didn't like that.

Build tested on loongarch (with CONFIG_KSTACK_ERASE=y) and m68k
(with CONFIG_DEBUG_STACK_USAGE=y).

Fixes: a45728fd4120 ("LoongArch: Enable HAVE_ARCH_STACKLEAK")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/all/20250726004313.GA3650901@ax162
Cc: Youling Tang <tangyouling@kylinos.cn>
Cc: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Kees Cook <kees@kernel.org>
---
 include/linux/sched/task_stack.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/sched/task_stack.h b/include/linux/sched/task_stack.h
index 85c5a6392e02..1fab7e9043a3 100644
--- a/include/linux/sched/task_stack.h
+++ b/include/linux/sched/task_stack.h
@@ -53,7 +53,7 @@ static inline void setup_thread_stack(struct task_struct *p, struct task_struct
  * When the stack grows up, this is the highest address.
  * Beyond that position, we corrupt data on the next page.
  */
-static inline unsigned long *end_of_stack(struct task_struct *p)
+static inline unsigned long *end_of_stack(const struct task_struct *p)
 {
 #ifdef CONFIG_STACK_GROWSUP
 	return (unsigned long *)((unsigned long)task_thread_info(p) + THREAD_SIZE) - 1;
-- 
2.34.1

Re: [PATCH] sched/task_stack: Add missing const qualifier to end_of_stack()

[Nathan Chancellor]

On Sat, Jul 26, 2025 at 02:06:46PM -0700, Kees Cook wrote:
> Add missing const qualifier to the non-CONFIG_THREAD_INFO_IN_TASK
> version of end_of_stack() to match the CONFIG_THREAD_INFO_IN_TASK
> version. Fixes a warning with CONFIG_KSTACK_ERASE=y on archs that don't
> select THREAD_INFO_IN_TASK (such as LoongArch):
> 
>   error: passing 'const struct task_struct *' to parameter of type 'struct task_struct *' discards qualifiers
> 
> The stackleak_task_low_bound() function correctly uses a const task
> parameter, but the legacy end_of_stack() prototype didn't like that.
> 
> Build tested on loongarch (with CONFIG_KSTACK_ERASE=y) and m68k
> (with CONFIG_DEBUG_STACK_USAGE=y).
> 
> Fixes: a45728fd4120 ("LoongArch: Enable HAVE_ARCH_STACKLEAK")
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Closes: https://lore.kernel.org/all/20250726004313.GA3650901@ax162
> Cc: Youling Tang <tangyouling@kylinos.cn>
> Cc: Huacai Chen <chenhuacai@loongson.cn>
> Signed-off-by: Kees Cook <kees@kernel.org>

Tested-by: Nathan Chancellor <nathan@kernel.org>

> ---
>  include/linux/sched/task_stack.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/sched/task_stack.h b/include/linux/sched/task_stack.h
> index 85c5a6392e02..1fab7e9043a3 100644
> --- a/include/linux/sched/task_stack.h
> +++ b/include/linux/sched/task_stack.h
> @@ -53,7 +53,7 @@ static inline void setup_thread_stack(struct task_struct *p, struct task_struct
>   * When the stack grows up, this is the highest address.
>   * Beyond that position, we corrupt data on the next page.
>   */
> -static inline unsigned long *end_of_stack(struct task_struct *p)
> +static inline unsigned long *end_of_stack(const struct task_struct *p)
>  {
>  #ifdef CONFIG_STACK_GROWSUP
>  	return (unsigned long *)((unsigned long)task_thread_info(p) + THREAD_SIZE) - 1;
> -- 
> 2.34.1
>