| Message ID | 20210426074935.11131-2-sherry.sun@nxp.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Fix two coverity issues in fsl_lpuart.c | expand |
Hi Greg, > -----Original Message----- > From: Greg KH <gregkh@linuxfoundation.org> > Sent: 2021年4月26日 16:09 > To: Sherry Sun <sherry.sun@nxp.com> > Cc: jirislaby@kernel.org; linux-serial@vger.kernel.org; linux- > kernel@vger.kernel.org; dl-linux-imx <linux-imx@nxp.com> > Subject: Re: [PATCH 1/2] tty: serial: fsl_lpuart: fix the potential bug of division > or modulo by zero > > On Mon, Apr 26, 2021 at 03:49:34PM +0800, Sherry Sun wrote: > > This issue is reported by Coverity Check. > > In lpuart32_console_get_options, division or modulo by zero may > > results in undefined behavior. > > > > Signed-off-by: Sherry Sun <sherry.sun@nxp.com> > > --- > > drivers/tty/serial/fsl_lpuart.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/drivers/tty/serial/fsl_lpuart.c > > b/drivers/tty/serial/fsl_lpuart.c index 794035041744..777d54b593f8 > > 100644 > > --- a/drivers/tty/serial/fsl_lpuart.c > > +++ b/drivers/tty/serial/fsl_lpuart.c > > @@ -2414,6 +2414,9 @@ lpuart32_console_get_options(struct lpuart_port > > *sport, int *baud, > > > > bd = lpuart32_read(&sport->port, UARTBAUD); > > bd &= UARTBAUD_SBR_MASK; > > + if (!bd) > > + return; > > How can this ever happen? > > Not to say this is a bad check, but it feels like this can't really happen in real > life, what code patch could create this result? > > And have you tested this on real hardware? > Thanks for the reviewing, yes, I have tested the patchset on the real hardware. Seems the coverity check is static scan, so cannot judge if UARTBAUD Register will be zero. I just found below statement in the uart reference manual: "When SBR is 1 - 8191, the baud rate equals "baud clock / ((OSR+1) × SBR)"." Since I am not familiar with uart, do you mean that the value of UARTBAUD Register will never be zero, so this case will not happen in real word? If yes, I will drop this patch. Best regards Sherry > thanks, > > greg k-h
Hi Greg, > > > > > > > > > > > > > Thanks for the reviewing, yes, I have tested the patchset on the > > > > real > > > hardware. > > > > > > > > Seems the coverity check is static scan, so cannot judge if > > > > UARTBAUD > > > Register will be zero. > > > > I just found below statement in the uart reference manual: "When > > > > SBR is 1 > > > - 8191, the baud rate equals "baud clock / ((OSR+1) × SBR)"." > > > > Since I am not familiar with uart, do you mean that the value of > > > > UARTBAUD > > > Register will never be zero, so this case will not happen in real word? > > > > > > Given that this never has happened with hardware for such an old > > > device, perhaps it is impossible. But it would be good to check. > > > > > > > If yes, I will drop this patch. > > > > > > Handling "bad data" from hardware is never a bad idea, so I don't > > > necessarily want to drop this patch, I just want to try to figure > > > out if this is a "incase the hardware is broken/malicious" type of change, > vs. > > > a "this bug we are seeing in real hardware" type of change. > > > > > > > Yes, you are right, the probability of hardware happen in this case is really > low. But we cannot guarantee that it will never happen. > > So will this check here be accepted? Thanks! > > Please resubmit it with a better changelog description summarizing the > discussion here to make it more obvious why this change is needed. > Sure, will send a V2 patch with a better commit description. Thanks! Best regards Sherry > thanks, > > greg k-h
diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c index 794035041744..777d54b593f8 100644 --- a/drivers/tty/serial/fsl_lpuart.c +++ b/drivers/tty/serial/fsl_lpuart.c @@ -2414,6 +2414,9 @@ lpuart32_console_get_options(struct lpuart_port *sport, int *baud, bd = lpuart32_read(&sport->port, UARTBAUD); bd &= UARTBAUD_SBR_MASK; + if (!bd) + return; + sbr = bd; uartclk = lpuart_get_baud_clk_rate(sport); /*
This issue is reported by Coverity Check. In lpuart32_console_get_options, division or modulo by zero may results in undefined behavior. Signed-off-by: Sherry Sun <sherry.sun@nxp.com> --- drivers/tty/serial/fsl_lpuart.c | 3 +++ 1 file changed, 3 insertions(+)