Re: [PATCH] clk: Guard clk_round_rate() against error pointers

Sebastian Reichel <[email protected]> Fri, 24 Jul 2026 23:40:19 +0200
Newsgroups	org.kernel.vger.linux-clk,org.kernel.vger.linux-kernel
Message-ID	<amPY3TNEFwtlpzWw@venus>
Hi,

On Fri, Jul 24, 2026 at 11:44:55AM -0400, Brian Masney wrote:
> Hi Praveen,
> 
> On Thu, Jul 23, 2026 at 10:10:06PM +0530, Praveen Talari wrote:
> > On 23-07-2026 19:59, Brian Masney wrote:
> > > On Thu, Jul 23, 2026 at 11:40:47AM +0530, Praveen Talari wrote:
> > > > clk_round_rate() only checks for a NULL clk pointer before
> > > > dereferencing it, but callers such as dev_pm_opp_set_rate() can pass
> > > > it an error pointer (e.g. ERR_PTR(-ENOENT) left behind by
> > > > clk_get() when a device has no Linux clock and is instead managed by
> > > > firmware via a genpd/OPP performance domain).
> > > > 
> > > > Dereferencing that error pointer to read clk->exclusive_count
> > > > crashes with an unhandled kernel NULL pointer dereference, since
> > > > ERR_PTR(-ENOENT) plus the field's offset lands on a small, unmapped
> > > > address:
> > > > 
> > > >    Unable to handle kernel NULL pointer dereference at virtual
> > > >    address 000000000000002e
> > > >    ...
> > > >    pc : clk_round_rate+0x3c/0x188
> > > >    ...
> > > >    Call trace:
> > > >     clk_round_rate+0x3c/0x188 (P)
> > > >     dev_pm_opp_set_rate+0x114/0x33c
> > > > 
> > > > Change the guard from "if (!clk)" to "if (IS_ERR_OR_NULL(clk))",
> > > > matching the pattern already used by other clk consumer API
> > > > functions such as clk_unprepare(), so an error pointer is rejected
> > > > the same way a NULL pointer is.
> > > > 
> > > > Signed-off-by: Praveen Talari <[email protected]>
> > > > ---
> > > >   drivers/clk/clk.c | 2 +-
> > > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > > > index 048adfa86a5d..8c1ad3d10284 100644
> > > > --- a/drivers/clk/clk.c
> > > > +++ b/drivers/clk/clk.c
> > > > @@ -1780,7 +1780,7 @@ long clk_round_rate(struct clk *clk, unsigned long rate)
> > > >   	struct clk_rate_request req;
> > > >   	int ret;
> > > > -	if (!clk)
> > > > +	if (IS_ERR_OR_NULL(clk))
> > > Can you provide more details about the clk_get() call point that starts this
> > > error? Specifically which driver this occurs in and the exact scenario that
> > > triggers this.
> > 
> > On SA8255P platform there is no Linux
> > clock for the SE, and the perf domain device's OPPs are populated entirely
> > from firmware via devm_pm_opp_of_add_table() (through
> > of_genpd_add_provider_simple()/onecell()), so the perf domain's OPP table
> > has entries even though no clk_get() ever succeeds for it.
> > 
> > The clk_get(-ENOENT) case comes from _update_opp_table_clk() in
> > drivers/opp/core.c:
> > 
> >     opp_table->clk = clk_get(dev, NULL);
> >     ret = PTR_ERR_OR_ZERO(opp_table->clk);
> >     ...
> >     if (ret == -ENOENT) {
> >         /* ... no clk provided ... */
> >         opp_table->clk_count = 1;
> >         return opp_table;   /* opp_table->clk left as ERR_PTR(-ENOENT) */
> >     }
> > 
> > Because the perf domain device has no "clocks" property (its OPPs are
> > supplied purely as performance states by firmware/genpd), clk_get()
> > returns -ENOENT, and opp_table->clk is left holding that error pointer
> > rather than being reset to NULL.
> 
> This looks to be a reasonable change. Thanks.
> 
> Reviewed-by: Brian Masney <[email protected]>

I suggest to instead change the OPP code, so that it calls
clk_get_optional() instead of clk_get() and thus properly
"document" that the clock is optional and use the NULL dummy
clock (it's also shorter):

/*
 * There are few platforms which don't want the OPP core to
 * manage device's clock settings. In such cases neither the
 * platform provides the clks explicitly to us, nor the DT
 * contains a valid clk entry. The OPP nodes in DT may still
 * contain "opp-hz" property though, which we need to parse and
 * allow the platform to find an OPP based on freq later on.
 *
 * This is a simple solution to take care of such corner cases,
 * i.e. make the clk_count 1, which lets us allocate space for
 * frequency in opp->rates and also parse the entries in DT.
 */
opp_table->clk = clk_get_optional(dev, NULL);

ret = PTR_ERR_OR_ZERO(opp_table->clk);
if (ret) {
    dev_pm_opp_put_opp_table(opp_table);
    dev_err_probe(dev, ret, "Couldn't find clock\n");
    return ERR_PTR(ret);
}

if (opp_table->clk)
    opp_table->config_clks = _opp_config_clk_single;
opp_table->clk_count = 1;
return opp_table;

Greetings,

-- Sebastian
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