linux-kernel - Re: [PATCH 6/7] i915: Convert to verify_page

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Message-ID: <YHVAKeYh04y5w7ia@hirez.programming.kicks-ass.net>
Date:   Tue, 13 Apr 2021 08:54:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        sstabellini@...nel.org, x86@...nel.org,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, chris@...is-wilson.co.uk,
        intel-gfx@...ts.freedesktop.org, linux-mm@...ck.org, hch@....de
Subject: Re: [PATCH 6/7] i915: Convert to verify_page_range()

On Mon, Apr 12, 2021 at 01:08:38PM -0700, Kees Cook wrote:
> On Mon, Apr 12, 2021 at 10:00:18AM +0200, Peter Zijlstra wrote:
> > @@ -1249,14 +1249,14 @@ static int check_absent_pte(pte_t *pte,
> >  
> >  static int check_present(unsigned long addr, unsigned long len)
> >  {
> > -	return apply_to_page_range(current->mm, addr, len,
> > -				   check_present_pte, (void *)addr);
> > +	return verify_page_range(current->mm, addr, len,
> > +				 check_present_pte, (void *)addr);
> 
> For example, switch to returning bad addr through verify_page_range(),
> or have a by-reference value, etc:
> 
> 	unsigned long failed;
> 
> 	failed = verify_page_range(current->mm< addr, len, check_present_pte);
> 	if (failed) {
>   		pr_err("missing PTE:%lx\n",
>   		       (addr - failed) >> PAGE_SHIFT);

OK, lemme try that.