Re: [PATCH] rtc: s5m: Remove VLA usage

[Gustavo A. R. Silva]

Hi Krzysztof,

On 03/09/2018 07:04 AM, Krzysztof Kozlowski wrote:
> On Thu, Mar 8, 2018 at 7:03 PM, Gustavo A. R. Silva
> <garsilva@xxxxxxxxxxxxxx> wrote:
> > On 03/08/2018 11:58 AM, Kees Cook wrote:
> > > On Thu, Mar 8, 2018 at 9:20 AM, Gustavo A. R. Silva
> > > <gustavo@xxxxxxxxxxxxxx> wrote:
> > > > In preparation to enabling -Wvla, remove VLAs and replace them
> > > > with fixed-length arrays instead.
> > > >
> > > >   From a security viewpoint, the use of Variable Length Arrays can be
> > > > a vector for stack overflow attacks. Also, in general, as the code
> > > > evolves it is easy to lose track of how big a VLA can get. Thus, we
> > > > can end up having segfaults that are hard to debug.
> > > >
> > > > Also, fixed as part of the directive to remove all VLAs from
> > > > the kernel: https://lkml.org/lkml/2018/3/7/621
> > > >
> > > > Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> > > > ---
> > > >    drivers/rtc/rtc-s5m.c | 15 +++++++++------
> > > >    1 file changed, 9 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/drivers/rtc/rtc-s5m.c b/drivers/rtc/rtc-s5m.c
> > > > index 6deae10..2b5f4f7 100644
> > > > --- a/drivers/rtc/rtc-s5m.c
> > > > +++ b/drivers/rtc/rtc-s5m.c
> > > > @@ -38,6 +38,9 @@
> > > >     */
> > > >    #define UDR_READ_RETRY_CNT     5
> > > >
> > > > +/* Maximum number of registers for setting time/alarm0/alarm1 */
> > > > +#define MAX_NUM_TIME_REGS      8
> > >
> > >
> > > I would adjust the various const struct s5m_rtc_reg_config's
> > > .regs_count to be represented by this new define, so the stack and the
> > > structures stay in sync. Something like:
> > >
> > > static const struct s5m_rtc_reg_config s2mps13_rtc_regs = {
> > >           .regs_count             = MAX_NUM_TIME_REGS - 1,
> > >
> > > ?
> >
> > Yep. I thought about that and decided to wait for some feedback first. But
> > yeah, I think is that'd be a good change.
>
> Define and these assignments should be somehow connected with enum
> defining the offsets for data[] (from
> include/linux/mfd/samsung/rtc.h). Otherwise we define the same in two
> places. The enum could be itself (in separate patch) moved to the
> driver because it is meaningless for others.

I got it.

I'll move the enum to rtc-s5m.c and add RTC_MAX_NUM_TIME_REGS at the end 
of it. I'll send a patch series for this.

Thanks for the feedback.
--
Gustavo

> Best regards,
> Krzysztof