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Date:   Mon, 19 Sep 2022 12:26:22 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Yu Zhao <yuzhao@...gle.com>, dev@...-flo.net,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-perf-users@...r.kernel.org,
        linux-mm@...ck.org, linux-hardening@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH 0/3] x86/dumpstack: Inline copy_from_user_nmi()

On Mon, Sep 19, 2022 at 04:46:39PM +0200, Peter Zijlstra wrote:
> On Fri, Sep 16, 2022 at 12:57:23PM -0700, Andrew Morton wrote:
> > Why is this so complicated.
> > 
> > There's virtually zero value in running all those debug checks from within
> > copy_from_user_nmi().
> > 
> > --- a/arch/x86/lib/usercopy.c~a
> > +++ a/arch/x86/lib/usercopy.c
> > @@ -44,7 +44,7 @@ copy_from_user_nmi(void *to, const void
> >  	 * called from other contexts.
> >  	 */
> >  	pagefault_disable();
> > -	ret = __copy_from_user_inatomic(to, from, n);
> > +	ret = raw_copy_from_user(to, from, n);
> >  	pagefault_enable();
> >  
> >  	return ret;
> 
> I'm with Andrew here; this looks a *LOT* saner than all the other stuff.

Yeah, I'd agree -- it's a special case of a special case. I'll send a
new patch.

Thanks!

-- 
Kees Cook

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