[CRIU] [RFT PATCH] compel/aarch64: fix off-by-one in compel_task_size

[Mike Rapoport]

On Mon, Aug 28, 2017 at 03:10:00PM +0300, Dmitry Safonov wrote:
> Hi Mike,
> 
> 2017-08-24 14:35 GMT+03:00 Mike Rapoport <rppt at linux.vnet.ibm.com>:
> > Currently we are checking task sizes that are *less* than TASK_SIZE_MAX and
> > we never check with task_size == TASK_SIZE_MAX. Fix it.
> >
> > Signed-off-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
> > ---
> >
> > I don't have an aarch64 platform handy and I'll appreciate if someone can
> > verify that this patch actually works...
> 
> Well, AFAICS the same logic works for arm32, so you need to
> patch it also (or edit commit message explaining why it's good
> for arm32).
> 
> >
> >
> >  compel/arch/aarch64/src/lib/infect.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/compel/arch/aarch64/src/lib/infect.c b/compel/arch/aarch64/src/lib/infect.c
> > index 166ec23..25c60c6 100644
> > --- a/compel/arch/aarch64/src/lib/infect.c
> > +++ b/compel/arch/aarch64/src/lib/infect.c
> > @@ -165,9 +165,8 @@ unsigned long compel_task_size(void)
> >  {
> >         unsigned long task_size;
> >
> > -       for (task_size = TASK_SIZE_MIN; task_size < TASK_SIZE_MAX; task_size <<= 1)
> > +       for (task_size = TASK_SIZE_MIN; task_size <= TASK_SIZE_MAX; task_size <<= 1)
> >                 if (munmap((void *)task_size, page_size()))
> >                         break;
> >         return task_size;
> 
> I'm not sure the change is valid:
> address is in kernel space if (>= TASK_SIZE), so trying to
> munmap(TASK_SIZE_MAX) will
> *always* fail.
> So we already test if task has 48-bit VA (TASK_SIZE) by unmapping
> (TASK_SIZE_MAX >> 1)
> on a previous cycle. If it succeed the task_size will be == TASK_SIZE_MAX.

Sad to admit, but Yeah, you are right.

> Maybe it's worth a comment here ;-)

Care to add one? ;-)
 
> >  }
> > -
> > --
> > 2.7.4
> >
> > _______________________________________________
> > CRIU mailing list
> > CRIU at openvz.org
> > https://lists.openvz.org/mailman/listinfo/criu
> 
> 
> 
> -- 
>              Dmitry
> 

-- 
Sincerely yours,
Mike.