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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.09.17 at 17:01, <wei.liu2@xxxxxxxxxx> wrote:
> 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.

I would prefer that.

> It's you and Andrew's call.

Andrew?

Jan


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