Re: [PATCH] RDMA/hns: Use 64-bit arithmetic instead of 32-bit

[Doug Ledford]

On Thu, 2018-10-18 at 14:01 +0300, Leon Romanovsky wrote:
> On Thu, Oct 18, 2018 at 10:02:58AM +0200, Gustavo A. R. Silva wrote:
> > Cast *max_num_sg* to u64 in order to give the compiler complete
> > information about the proper arithmetic to use.
> > 
> > Notice that such variable is used in a context that expects an
> > expression of type u64 (64 bits, unsigned) and the following
> > expression is currently being evaluated using 32-bit
> > arithmetic:
> 
> And what is wrong with that?
> Please fix static analyzer tool instead of fixing proper C code.

Judging on the static analyzer tool's message, I don't see anything
wrong with it.  The code contains a potential unintentional overflow
error.  The author might have been well aware of the overflow and not
cared and in that case this is valid C, but the analyzer has no way of
knowing that, so it flags it for review.  To silence the checker you
could either cast the arithmetic to u64, or cast length to u32.  Either
would clear up the ambiguity.  I guess I'm not seeing why you would
blame the static checker in this case, it did the best it is possible
for it to do.

> Thanks
> 
> > 
> > length = max_num_sg * page_size;
> > 
> > Addresses-Coverity-ID: 1474517 ("Unintentional integer overflow")
> > Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> > ---
> >  drivers/infiniband/hw/hns/hns_roce_mr.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/infiniband/hw/hns/hns_roce_mr.c b/drivers/infiniband/hw/hns/hns_roce_mr.c
> > index 521ad2a..d479d5e 100644
> > --- a/drivers/infiniband/hw/hns/hns_roce_mr.c
> > +++ b/drivers/infiniband/hw/hns/hns_roce_mr.c
> > @@ -1219,7 +1219,7 @@ struct ib_mr *hns_roce_alloc_mr(struct ib_pd *pd, enum ib_mr_type mr_type,
> >  	int ret;
> > 
> >  	page_size = 1 << (hr_dev->caps.pbl_buf_pg_sz + PAGE_SHIFT);
> > -	length = max_num_sg * page_size;
> > +	length = (u64)max_num_sg * page_size;
> > 
> >  	if (mr_type != IB_MR_TYPE_MEM_REG)
> >  		return ERR_PTR(-EINVAL);
> > --
> > 2.7.4
> > 

-- 
Doug Ledford <dledford@xxxxxxxxxx>
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