Re: [PATCH] scs: Fix a wrong parameter in __scs_magic

[Will Deacon]

On Sat, Oct 11, 2025 at 10:11:17AM -0700, Andrew Morton wrote:
> On Sat, 11 Oct 2025 16:22:22 +0800 Zhichi Lin <zhichi.lin@xxxxxxxx> 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?

Apologies for the slow reply, I was away for a couple of weeks.

It looks like you've already put this in -next (thank you!), so please
go ahead and send it to Linus as a fix.

Acked-by: Will Deacon <will@xxxxxxxxxx>

Cheers,

Will