Re: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border

From: Thomas Gleixner <tglx@linutronix.de>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Ingo Molnar <mingo@redhat.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Nicholas Piggin <npiggin@gmail.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border
Date: Tue, 14 Nov 2017 21:54:52 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.20.1711142131010.2221@nanos> (raw)
In-Reply-To: <20171114202102.crpgiwgv2lu5aboq@node.shutemov.name>

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

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