From: Colin Ian King <[email protected]>
The shifting of buf[5] by 24 bits to the left will be promoted to
a 32 bit signed int and then sign-extended to an unsigned long. If
the top bit of buf[5] is set then all then all the upper bits sec
end up as also being set because of the sign-extension. Fix this by
casting buf[5] to an unsigned long before the shift.
Detected by CoverityScan, CID#1465292 ("Unintended sign extension")
Fixes: 0e1492330cd2 ("rtc: add rtc-tx4939 driver")
Signed-off-by: Colin Ian King <[email protected]>
---
drivers/rtc/rtc-tx4939.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/rtc/rtc-tx4939.c b/drivers/rtc/rtc-tx4939.c
index feededce3ded..1f351308afdc 100644
--- a/drivers/rtc/rtc-tx4939.c
+++ b/drivers/rtc/rtc-tx4939.c
@@ -109,7 +109,8 @@ static int tx4939_rtc_read_time(struct device *dev, struct rtc_time *tm)
for (i = 2; i < 6; i++)
buf[i] = __raw_readl(&rtcreg->dat);
spin_unlock_irq(&pdata->lock);
- sec = (buf[5] << 24) | (buf[4] << 16) | (buf[3] << 8) | buf[2];
+ sec = ((unsigned long)buf[5] << 24) | (buf[4] << 16) |
+ (buf[3] << 8) | buf[2];
rtc_time_to_tm(sec, tm);
return rtc_valid_tm(tm);
}
@@ -170,7 +171,8 @@ static int tx4939_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
alrm->enabled = (ctl & TX4939_RTCCTL_ALME) ? 1 : 0;
alrm->pending = (ctl & TX4939_RTCCTL_ALMD) ? 1 : 0;
spin_unlock_irq(&pdata->lock);
- sec = (buf[5] << 24) | (buf[4] << 16) | (buf[3] << 8) | buf[2];
+ sec = ((unsigned long)buf[5] << 24) | (buf[4] << 16) |
+ (buf[3] << 8) | buf[2];
rtc_time_to_tm(sec, &alrm->time);
return rtc_valid_tm(&alrm->time);
}
--
2.15.1
On 15/02/2018 at 19:36:14 +0000, Colin King wrote:
> From: Colin Ian King <[email protected]>
>
> The shifting of buf[5] by 24 bits to the left will be promoted to
> a 32 bit signed int and then sign-extended to an unsigned long. If
> the top bit of buf[5] is set then all then all the upper bits sec
> end up as also being set because of the sign-extension. Fix this by
> casting buf[5] to an unsigned long before the shift.
>
The timing of the discovery of this issue is suspicious. I believe it is
because I just enabled COMPILE_TEST on that driver and now this gets
compiled on a 64bit architecture.
Can I ask on which architecture this is an issue? I don't think (and a
small test program confirms) x86 does the sign extension because both
sec and buf are unsigned.
> Detected by CoverityScan, CID#1465292 ("Unintended sign extension")
>
> Fixes: 0e1492330cd2 ("rtc: add rtc-tx4939 driver")
> Signed-off-by: Colin Ian King <[email protected]>
> ---
> drivers/rtc/rtc-tx4939.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/rtc/rtc-tx4939.c b/drivers/rtc/rtc-tx4939.c
> index feededce3ded..1f351308afdc 100644
> --- a/drivers/rtc/rtc-tx4939.c
> +++ b/drivers/rtc/rtc-tx4939.c
> @@ -109,7 +109,8 @@ static int tx4939_rtc_read_time(struct device *dev, struct rtc_time *tm)
> for (i = 2; i < 6; i++)
> buf[i] = __raw_readl(&rtcreg->dat);
> spin_unlock_irq(&pdata->lock);
> - sec = (buf[5] << 24) | (buf[4] << 16) | (buf[3] << 8) | buf[2];
> + sec = ((unsigned long)buf[5] << 24) | (buf[4] << 16) |
> + (buf[3] << 8) | buf[2];
> rtc_time_to_tm(sec, tm);
> return rtc_valid_tm(tm);
> }
> @@ -170,7 +171,8 @@ static int tx4939_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
> alrm->enabled = (ctl & TX4939_RTCCTL_ALME) ? 1 : 0;
> alrm->pending = (ctl & TX4939_RTCCTL_ALMD) ? 1 : 0;
> spin_unlock_irq(&pdata->lock);
> - sec = (buf[5] << 24) | (buf[4] << 16) | (buf[3] << 8) | buf[2];
> + sec = ((unsigned long)buf[5] << 24) | (buf[4] << 16) |
> + (buf[3] << 8) | buf[2];
> rtc_time_to_tm(sec, &alrm->time);
> return rtc_valid_tm(&alrm->time);
> }
> --
> 2.15.1
>
--
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com
On 15/02/2018 at 21:44:53 +0100, Alexandre Belloni wrote:
> On 15/02/2018 at 19:36:14 +0000, Colin King wrote:
> > From: Colin Ian King <[email protected]>
> >
> > The shifting of buf[5] by 24 bits to the left will be promoted to
> > a 32 bit signed int and then sign-extended to an unsigned long. If
> > the top bit of buf[5] is set then all then all the upper bits sec
> > end up as also being set because of the sign-extension. Fix this by
> > casting buf[5] to an unsigned long before the shift.
> >
>
> The timing of the discovery of this issue is suspicious. I believe it is
> because I just enabled COMPILE_TEST on that driver and now this gets
> compiled on a 64bit architecture.
>
> Can I ask on which architecture this is an issue? I don't think (and a
> small test program confirms) x86 does the sign extension because both
> sec and buf are unsigned.
>
Actually, my test program was wrong and you are right.
--
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com
On 16/02/18 15:24, Alexandre Belloni wrote:
> On 15/02/2018 at 21:44:53 +0100, Alexandre Belloni wrote:
>> On 15/02/2018 at 19:36:14 +0000, Colin King wrote:
>>> From: Colin Ian King <[email protected]>
>>>
>>> The shifting of buf[5] by 24 bits to the left will be promoted to
>>> a 32 bit signed int and then sign-extended to an unsigned long. If
>>> the top bit of buf[5] is set then all then all the upper bits sec
>>> end up as also being set because of the sign-extension. Fix this by
>>> casting buf[5] to an unsigned long before the shift.
>>>
>>
>> The timing of the discovery of this issue is suspicious. I believe it is
>> because I just enabled COMPILE_TEST on that driver and now this gets
>> compiled on a 64bit architecture.
>>
>> Can I ask on which architecture this is an issue? I don't think (and a
>> small test program confirms) x86 does the sign extension because both
>> sec and buf are unsigned.
>>
>
> Actually, my test program was wrong and you are right.
> Kudos to CoverityScan static analysis for finding it. It's not obvious
for sure
Colin
On 15/02/2018 at 19:36:14 +0000, Colin King wrote:
> From: Colin Ian King <[email protected]>
>
> The shifting of buf[5] by 24 bits to the left will be promoted to
> a 32 bit signed int and then sign-extended to an unsigned long. If
> the top bit of buf[5] is set then all then all the upper bits sec
> end up as also being set because of the sign-extension. Fix this by
> casting buf[5] to an unsigned long before the shift.
>
> Detected by CoverityScan, CID#1465292 ("Unintended sign extension")
>
> Fixes: 0e1492330cd2 ("rtc: add rtc-tx4939 driver")
> Signed-off-by: Colin Ian King <[email protected]>
> ---
> drivers/rtc/rtc-tx4939.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
Applied, thanks.
--
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com