linux-kernel - [PATCH AUTOSEL 4.14 38/39] task_stack: Fix end_of_stack() for architectures with upwards-growing stack

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Message-Id: <20211109010649.1191041-38-sashal@kernel.org>
Date:   Mon,  8 Nov 2021 20:06:48 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Helge Deller <deller@....de>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.14 38/39] task_stack: Fix end_of_stack() for architectures with upwards-growing stack

From: Helge Deller <deller@....de>

[ Upstream commit 9cc2fa4f4a92ccc6760d764e7341be46ee8aaaa1 ]

The function end_of_stack() returns a pointer to the last entry of a
stack. For architectures like parisc where the stack grows upwards
return the pointer to the highest address in the stack.

Without this change I faced a crash on parisc, because the stackleak
functionality wrote STACKLEAK_POISON to the lowest address and thus
overwrote the first 4 bytes of the task_struct which included the
TIF_FLAGS.

Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 include/linux/sched/task_stack.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/sched/task_stack.h b/include/linux/sched/task_stack.h
index cb4828aaa34fd..3461beb89b040 100644
--- a/include/linux/sched/task_stack.h
+++ b/include/linux/sched/task_stack.h
@@ -25,7 +25,11 @@ static inline void *task_stack_page(const struct task_struct *task)
 
 static inline unsigned long *end_of_stack(const struct task_struct *task)
 {
+#ifdef CONFIG_STACK_GROWSUP
+	return (unsigned long *)((unsigned long)task->stack + THREAD_SIZE) - 1;
+#else
 	return task->stack;
+#endif
 }
 
 #elif !defined(__HAVE_THREAD_FUNCTIONS)
-- 
2.33.0