Re: [PATCH v5 04/14] coresight: cti: Add sysfs trigger / channel programming API

Mike Leach
2019-11-29T13:02:00Z

Hi Suzuki,

On Wed, 27 Nov 2019 at 18:40, Suzuki Kuruppassery Poulose
<suzuki.poulose@arm.com> wrote:
>
> On 19/11/2019 23:19, Mike Leach wrote:
> > Adds a user API to allow programming of CTI by trigger ID and
> > channel number. This will take the channel and trigger ID supplied
> > by the user and program the appropriate register values.
> >
> > Signed-off-by: Mike Leach <mike.leach@linaro.org>
> > ---
>
> > +
> > +static ssize_t chan_xtrigs_view_show(struct device *dev,
> > + struct device_attribute *attr,
> > + char *buf)
> > +{
> > + struct cti_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > + struct cti_config *cfg = &drvdata->config;
> > + int used = 0, reg_idx;
> > + int buf_sz = PAGE_SIZE;
> > + u32 chan_mask = BIT(cfg->xtrig_rchan_sel);
> > +
> > + used += scnprintf(buf, buf_sz, "[%d] IN: ", cfg->xtrig_rchan_sel);
> > + for (reg_idx = 0;
> > + reg_idx < drvdata->config.nr_trig_max;
> > + reg_idx++) {
> > + if (chan_mask & cfg->ctiinen[reg_idx]) {
> > + used += scnprintf(buf + used, buf_sz - used, "%d ",
> > + reg_idx);
> > + }
> > + }
>
> As a security measure, we must make sure that we have space left in the
> buffer. We could end up passing "negative" numbers for the size
> argument, in the worst case.
>

The return value from scnprintf() is always the _actual_ number of
characters added to the buffer, not as per snprintf() which returns
the number that could have been printed if there were sufficient
space.
Thus used can never exceed the buffer size.

Regards

Mike

> > +
> > + used += scnprintf(buf + used, buf_sz - used, "OUT: ");
> > + for (reg_idx = 0;
> > + reg_idx < drvdata->config.nr_trig_max;
> > + reg_idx++) {
> > + if (chan_mask & cfg->ctiouten[reg_idx]) {
> > + used += scnprintf(buf + used, buf_sz - used, "%d ",
> > + reg_idx);
> > + }
> > + }
> > + used += scnprintf(buf + used, buf_sz - used, "\n");
> > + return used;
> > +}
> > +static DEVICE_ATTR_RW(chan_xtrigs_view);
>
>
> The rest looks fine to me.
>
> Suzuki

--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK