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SubjectRe: [PATCH] x86: do not overrun page table ranges in gup
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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