Messages in this thread | | | Date | Wed, 15 Nov 2017 14:27:02 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border |
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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'.
-- Kirill A. Shutemov
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