From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Helge Deller <deller@gmx.de>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 177/355] task_stack: Fix end_of_stack() for architectures with upwards-growing stack
Date:   Mon, 15 Nov 2021 18:01:41 +0100
Message-Id: <20211115165319.511324574@linuxfoundation.org>
In-Reply-To: <20211115165313.549179499@linuxfoundation.org>
References: <20211115165313.549179499@linuxfoundation.org>
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From: Helge Deller <deller@gmx.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@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.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 2413427e439c7..d10150587d819 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