linux-kernel - Re: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP

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Date:   Tue, 14 Nov 2017 21:54:52 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Nicholas Piggin <npiggin@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across
 DEFAULT_MAP_WINDOW border

On Tue, 14 Nov 2017, Kirill A. Shutemov wrote:

> On Tue, Nov 14, 2017 at 05:01:50PM +0100, Thomas Gleixner wrote:
> > @@ -198,11 +199,14 @@ arch_get_unmapped_area_topdown(struct fi
> >  	/* requesting a specific address */
> >  	if (addr) {
> >  		addr = PAGE_ALIGN(addr);
> > +		if (!mmap_address_hint_valid(addr, len))
> > +			goto get_unmapped_area;
> > +
> 
> Here and in hugetlb_get_unmapped_area(), we should align the addr after
> the check, not before. Otherwise the alignment itself can bring us over
> the borderline as we align up.

Hmm, then I wonder whether the next check against vm_start_gap() which
checks against the aligned address is correct:

                addr = PAGE_ALIGN(addr);
                vma = find_vma(mm, addr);

                if (end - len >= addr &&
                    (!vma || addr + len <= vm_start_gap(vma)))
                        return addr;

Thanks,

	tglx