From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Thomas Gleixner <tglx@linutronix.de>
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: Wed, 15 Nov 2017 15:10:42 +0300 [thread overview]
Message-ID: <20171115121042.dt2us5fsuqmepx4i@node.shutemov.name> (raw)
In-Reply-To: <alpine.DEB.2.20.1711151238500.1805@nanos>
On Wed, Nov 15, 2017 at 12:39:40PM +0100, Thomas Gleixner wrote:
> On Wed, 15 Nov 2017, Kirill A. Shutemov wrote:
> > On Wed, Nov 15, 2017 at 12:00:46AM +0100, Thomas Gleixner wrote:
> > > On Wed, 15 Nov 2017, Kirill A. Shutemov wrote:
> > > > On Tue, Nov 14, 2017 at 09:54:52PM +0100, Thomas Gleixner wrote:
> > > > > 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;
> > > >
> > > > I think the check is correct. The check is against resulting addresses
> > > > that end up in vm_start/vm_end. In our case we want to figure out what
> > > > user asked for.
> > >
> > > Well, but then checking just against the user supplied addr is only half of
> > > the story.
> > >
> > > addr = boundary - PAGE_SIZE - PAGE_SIZE / 2;
> > > len = PAGE_SIZE - PAGE_SIZE / 2;
> > >
> > > That fits, but then after alignment we end up with
> > >
> > > addr = boudary - PAGE_SIZE;
> > >
> > > and due to len > PAGE_SIZE this will result in a mapping which crosses the
> > > boundary, right? So checking against the PAGE_ALIGN(addr) should be the
> > > right thing to do.
> >
> > IIUC, this is only the case if 'len' is not aligned, right?
> >
> > >From what I see we expect caller to align it (and mm/mmap.c does this, I
> > haven't checked other callers).
> >
> > And hugetlb would actively reject non-aligned len.
> >
> > I *think* we should be fine with checking unaligned 'addr'.
>
> I think we should keep it consistent for the normal and the huge case and
> just check aligned and be done with it.
Aligned 'addr'? Or 'len'? Both?
We would have problem with checking aligned addr. I steped it in hugetlb
case:
- User asks for mmap((1UL << 47) - PAGE_SIZE, 2 << 20, MAP_HUGETLB);
- On 4-level paging machine this gives us invalid hint address as
'TASK_SIZE - len' is more than 'addr'. Goto get_unmapped_area.
- On 5-level paging machine hint address gets rounded up to next 2MB
boundary that is exactly 1UL << 47 and we happily allocate from full
address space which may lead to trouble.
--
Kirill A. Shutemov
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next prev parent reply other threads:[~2017-11-15 12:10 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-14 13:43 [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border Kirill A. Shutemov
2017-11-14 13:43 ` [PATCHv2 2/2] x86/selftests: Add test for mapping placement for 5-level paging Kirill A. Shutemov
2017-11-14 16:01 ` [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border Thomas Gleixner
2017-11-14 19:21 ` Kirill A. Shutemov
2017-11-14 20:29 ` Thomas Gleixner
2017-11-14 20:21 ` Kirill A. Shutemov
2017-11-14 20:54 ` Thomas Gleixner
2017-11-14 22:27 ` Kirill A. Shutemov
2017-11-14 23:00 ` Thomas Gleixner
2017-11-15 11:27 ` Kirill A. Shutemov
2017-11-15 11:39 ` Thomas Gleixner
2017-11-15 12:10 ` Kirill A. Shutemov [this message]
2017-11-15 14:04 ` Kirill A. Shutemov
2017-11-15 14:13 ` Kirill A. Shutemov
2017-11-15 14:23 ` Thomas Gleixner
2017-11-15 14:24 ` Kirill A. Shutemov
2017-11-15 14:18 ` Thomas Gleixner
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