linux-kernel - [PATCH] sched/task_stack: Add missing const qualifier to end_of

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Message-Id: <20250726210641.work.114-kees@kernel.org>
Date: Sat, 26 Jul 2025 14:06:46 -0700
From: Kees Cook <kees@...nel.org>
To: Youling Tang <tangyouling@...inos.cn>
Cc: Kees Cook <kees@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Huacai Chen <chenhuacai@...ngson.cn>,
	Huacai Chen <chenhuacai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	David Disseldorp <ddiss@...e.de>,
	Qun-Wei Lin <qun-wei.lin@...iatek.com>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH] sched/task_stack: Add missing const qualifier to end_of_stack()

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@...nel.org>
Closes: https://lore.kernel.org/all/20250726004313.GA3650901@ax162
Cc: Youling Tang <tangyouling@...inos.cn>
Cc: Huacai Chen <chenhuacai@...ngson.cn>
Signed-off-by: Kees Cook <kees@...nel.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