linux-kernel - Re: [PATCH 4/7] mm: Introduce verify_page

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Message-ID: <YHaS+4eV7ATwAAWz@hirez.programming.kicks-ass.net>
Date:   Wed, 14 Apr 2021 09:00:11 +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 4/7] mm: Introduce verify_page_range()

On Tue, Apr 13, 2021 at 08:01:08PM -0700, Kees Cook wrote:
> So the addr can just be encoded in "int", and no structure is needed at:
> 
> typedef bool (*vpr_fn_t)(pte_t pte);
> 
> static int vpr_fn(pte_t *pte, unsigned long addr, void *data)
> {
> 	vpr_fn_t callback = data;
> 
> 	if (!callback(*pte))
> 		return addr >> PAGE_SIZE;
> 	return 0;
> }
> 
> unsigned long verify_page_range(struct mm_struct *mm,
> 				unsigned long addr, unsigned long size,
> 				vpr_fn_t callback)
> {
> 	return apply_to_page_range(mm, addr, size, vpr_fn, callback) << PAGE_SIZE;
> }
> 
> But maybe I'm missing something?

That covers only (32+12) bits of address space and will mostly work, but
we definitely support architectures (very much including x86_64) with
larger address spaces than that.