On 20-10-27 11:03:29, Felipe Balbi wrote:
>
> Hi,
>
> Peter Chen <peter.chen@xxxxxxx> writes:
> > For code:
> > trb->length = cpu_to_le32(TRB_BURST_LEN(priv_ep->trb_burst_size)
> > | TRB_LEN(length));
> >
> > TRB_BURST_LEN(priv_ep->trb_burst_size) may be overflow for int 32 if
> > priv_ep->trb_burst_size is equal or larger than 0x80;
> >
> > Below is the Coverity warning:
> > sign_extension: Suspicious implicit sign extension: priv_ep->trb_burst_size
> > with type u8 (8 bits, unsigned) is promoted in priv_ep->trb_burst_size << 24
> > to type int (32 bits, signed), then sign-extended to type unsigned long
> > (64 bits, unsigned). If priv_ep->trb_burst_size << 24 is greater than 0x7FFFFFFF,
> > the upper bits of the result will all be 1.
>
> looks like a false positive...
>
> > Cc: <stable@xxxxxxxxxxxxxxx> #v5.8+
> > Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
> > Signed-off-by: Peter Chen <peter.chen@xxxxxxx>
> > ---
> > drivers/usb/cdns3/gadget.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/cdns3/gadget.h b/drivers/usb/cdns3/gadget.h
> > index 1ccecd237530..020936cb9897 100644
> > --- a/drivers/usb/cdns3/gadget.h
> > +++ b/drivers/usb/cdns3/gadget.h
> > @@ -1072,7 +1072,7 @@ struct cdns3_trb {
> > #define TRB_TDL_SS_SIZE_GET(p) (((p) & GENMASK(23, 17)) >> 17)
> >
> > /* transfer_len bitmasks - bits 31:24 */
> > -#define TRB_BURST_LEN(p) (((p) << 24) & GENMASK(31, 24))
> > +#define TRB_BURST_LEN(p) (unsigned int)(((p) << 24) & GENMASK(31, 24))
>
> ... because TRB_BURST_LEN() is used to intialize a __le32 type. Even if
> it ends up being sign extended, the top 32-bits will be ignored.
>
> I'll apply, but it looks like a pointless fix. We shouldn't need it for stable
>
At my v2:
It is:
#define TRB_BURST_LEN(p) ((unsigned int)((p) << 24) & GENMASK(31, 24))
It is not related to high 32-bits issue, it is sign extended issue for
32 bits. If p is a unsigned char data, the compiler will consider
(p) << 24 is int, but not unsigned int. So, if the p is larger than
0x80, the (p) << 24 will be overflow.
If you compile the code:
unsigned int k = 0x80 << 24 + 0x81;
It will report build warning:
warning: left shift count >= width of type [-Wshift-count-overflow]
--
Thanks,
Peter Chen
