From: Peter Chen
> Sent: 27 October 2020 09:49
>
> 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]
Something like:
#define TRB_BURST_LEN(p) (((p) + 0u) << 24)
will remove the warning.
The GENMASK() is pretty pointless - the compiler may fail to optimise
it away.
If p is 64bit the high bits should get discarded pretty quickly.
David
-
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Registration No: 1397386 (Wales)
