Messages in this thread | | | Date | Tue, 29 Jul 2008 02:25:07 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: [PATCH] x86: do not overrun page table ranges in gup |
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On Mon, 28 Jul 2008, Linus Torvalds wrote: > On Mon, 28 Jul 2008, Linus Torvalds wrote: > > > > So no, the right fix would be to align 'start' first, which means that > > everything else (including 'end') will be page-aligned. Aligning just one > > or the other is very very wrong. > > Does this work? > > Not pretty, but it stands _some_ chance of being correct. > > Linus
Acked-by: Hugh Dickins <hugh@veritas.com>
Seeing the bug report, I was working up a patch along the same lines as this; but got the access_ok() issue backwards: yours looks right. I see Alexey has tested it, confess I haven't.
> > > --- > arch/x86/mm/gup.c | 9 ++++++--- > 1 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c > index 3085f25..007bb06 100644 > --- a/arch/x86/mm/gup.c > +++ b/arch/x86/mm/gup.c > @@ -223,14 +223,17 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, > struct page **pages) > { > struct mm_struct *mm = current->mm; > - unsigned long end = start + (nr_pages << PAGE_SHIFT); > - unsigned long addr = start; > + unsigned long addr, len, end; > unsigned long next; > pgd_t *pgdp; > int nr = 0; > > + start &= PAGE_MASK; > + addr = start; > + len = (unsigned long) nr_pages << PAGE_SHIFT; > + end = start + len; > if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, > - start, nr_pages*PAGE_SIZE))) > + start, len))) > goto slow_irqon; > > /*
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