Re: [Xen-devel] [PATCH] hvmloader: cast to avoid potential overflow in shadow_gs_test

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Sep 11, 2017 at 08:55:53AM -0600, Jan Beulich wrote:
> >>> On 11.09.17 at 16:07, <wei.liu2@xxxxxxxxxx> wrote:
> > e2fc5bb5cb4 ("hvmloader: dynamically determine scratch memory range
> > for tests") makes the test dependent on _end. Coverity reported that
> > the shift might overflow and suggested we cast i to uint64_t.
> > 
> > Coverity-ID: 1417660
> > 
> > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > ---
> > Cc: Jan Beulich <jbeulich@xxxxxxxx>
> > Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > ---
> >  tools/firmware/hvmloader/tests.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/tools/firmware/hvmloader/tests.c 
> > b/tools/firmware/hvmloader/tests.c
> > index a70c72dffb..3c4c29a6c7 100644
> > --- a/tools/firmware/hvmloader/tests.c
> > +++ b/tools/firmware/hvmloader/tests.c
> > @@ -231,7 +231,7 @@ static int shadow_gs_test(void)
> >      pd += 512;
> >      /* Level 2: */
> >      for ( i = 0; i <= (unsigned long)(_end - 1) >> (PAGE_SHIFT + 9); i++ )
> 
> With the shift here there's no way ...
> 
> > -        *pd++ = (i << (PAGE_SHIFT + 9)) + 0x1e3;
> > +        *pd++ = ((uint64_t)i << (PAGE_SHIFT + 9)) + 0x1e3;
> 
> ... this shift (or the add) can overflow, irrespective of the actual
> value of _end, and with my dislike of casts I'm a little hesitant to
> give my ack for such a tool weakness workaround.

We can also mark that as false positive. It's you and Andrew's call.

I'm indifferent to the final solution.

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