Messages in this thread |  | | | Date | Fri, 24 Feb 2012 12:55:19 -0800 | | From | Andrew Morton <> | | Subject | Re: [PATCH] Ensure that walk_page_range()'s start and end are page-aligned |
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On Fri, 24 Feb 2012 11:19:25 -0800 Dan Smith <danms@us.ibm.com> wrote:
> > ... > > The inner function walk_pte_range() increments "addr" by PAGE_SIZE after > each pte is processed, and only exits the loop if the result is equal to > "end". Current, if either (or both of) the starting or ending addresses > passed to walk_page_range() are not page-aligned, then we will never > satisfy that exit condition and begin calling the pte_entry handler with > bad data. > > To be sure that we will land in the right spot, this patch checks that > both "addr" and "end" are page-aligned in walk_page_range() before starting > the traversal. > > ... > > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -196,6 +196,11 @@ int walk_page_range(unsigned long addr, unsigned long end, > if (addr >= end) > return err; > > + if (WARN_ONCE((addr & ~PAGE_MASK) || (end & ~PAGE_MASK), > + "address range is not page-aligned")) { > + return -EINVAL; > + } > + > if (!walk->mm) > return -EINVAL;
Well... why should we apply the patch? Is there some buggy code which is triggering the problem? Do you intend to write some buggy code to trigger the problem? ;)
IOW, what benefit is there to this change?
Also, as it's a developer-only thing we should arrange for the overhead to vanish when CONFIG_DEBUG_VM=n?
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