linux-kernel - Re: [PATCH] clocksource: atmel-st: Variable sr in at91rm9200_timer

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Message-ID: <CABvMjLRjeXAmhBwfZZPbmxdENq=FP9rR0Ld=T3veGXF6cjptxA@mail.gmail.com>
Date:   Mon, 2 Sep 2019 22:56:48 -0700
From:   Yizhuo Zhai <yzhai003@....edu>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Chengyu Song <csong@...ucr.edu>, Zhiyun Qian <zhiyunq@...ucr.edu>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] clocksource: atmel-st: Variable sr in at91rm9200_timer_interrupt()
 could be uninitialized

In function regmap_read(),  there're two places which could make the read fail.

First, if "reg" and  "map->reg_stride" are not aligned, then remap_read() will
return -EINVAL without initialize variable "val".

Second, _regmap_read() could also fail and return error code if "val" is not
initialized. The caller remap_read() returns the same error code, but
at91rm9200_timer_interrupt() does not use this information.

On Mon, Sep 2, 2019 at 3:37 PM Alexandre Belloni
<alexandre.belloni@...tlin.com> wrote:
>
> On 02/09/2019 15:29:46-0700, Yizhuo wrote:
> > Inside function at91rm9200_timer_interrupt(), variable sr could
> > be uninitialized if regmap_read() fails. However, sr is used
>
> Could you elaborate on how this could fail?
>
> > to decide the control flow later in the if statement, which is
> > potentially unsafe. We could check the return value of
> > regmap_read() and print an error here.
> >
> > Signed-off-by: Yizhuo <yzhai003@....edu>
> > ---
> >  drivers/clocksource/timer-atmel-st.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/clocksource/timer-atmel-st.c b/drivers/clocksource/timer-atmel-st.c
> > index ab0aabfae5f0..061a3f27847e 100644
> > --- a/drivers/clocksource/timer-atmel-st.c
> > +++ b/drivers/clocksource/timer-atmel-st.c
> > @@ -48,8 +48,14 @@ static inline unsigned long read_CRTR(void)
> >  static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id)
> >  {
> >       u32 sr;
> > +     int ret;
> > +
> > +     ret = regmap_read(regmap_st, AT91_ST_SR, &sr);
> > +     if (ret) {
> > +             pr_err("Fail to read AT91_ST_SR.\n");
> > +             return ret;
> > +     }
> >
> > -     regmap_read(regmap_st, AT91_ST_SR, &sr);
> >       sr &= irqmask;
> >
> >       /*
> > --
> > 2.17.1
> >
>
> --
> Alexandre Belloni, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com



-- 
Kind Regards,

Yizhuo Zhai

Computer Science, Graduate Student
University of California, Riverside