linux-kernel - Re: [PATCH] scs: Fix a wrong parameter in __scs

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Message-Id: <20251011101117.0b48ecef0dc7cfdd1f871273@linux-foundation.org>
Date: Sat, 11 Oct 2025 10:11:17 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Zhichi Lin <zhichi.lin@...o.com>
Cc: elver@...gle.com, will@...nel.org, andreyknvl@...il.com,
 samitolvanen@...gle.com, yee.lee@...iatek.com, keescook@...omium.org,
 linux-kernel@...r.kernel.org, xiejiyuan@...o.com
Subject: Re: [PATCH] scs: Fix a wrong parameter in __scs_magic

On Sat, 11 Oct 2025 16:22:22 +0800 Zhichi Lin <zhichi.lin@...o.com> wrote:

> __scs_magic() needs a 'void *' variable, but a 'struct task_struct *'
> is given. 'task_scs(tsk)' is the starting address of the task's shadow
> call stack, and '__scs_magic(task_scs(tsk))' is the end address of the
> task's shadow call stack.
> Here should be '__scs_magic(task_scs(tsk))'.

What are the userspace-visible runtime effects of this bug?  Please
always describe this when fixing something.

> Fixes: 5bbaf9d1fcb9 ("scs: Add support for stack usage debugging")

This might need backporting into -stable kernels, that depends on the
answer to the above question.

> --- a/kernel/scs.c
> +++ b/kernel/scs.c
> @@ -135,7 +135,7 @@ static void scs_check_usage(struct task_struct *tsk)
>  	if (!IS_ENABLED(CONFIG_DEBUG_STACK_USAGE))
>  		return;
>  
> -	for (p = task_scs(tsk); p < __scs_magic(tsk); ++p) {
> +	for (p = task_scs(tsk); p < __scs_magic(task_scs(tsk)); ++p) {
>  		if (!READ_ONCE_NOCHECK(*p))
>  			break;
>  		used += sizeof(*p);

Thanks, I'll grab the patch for now, maybe Will would prefer to take it?