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From:   Jernej =?utf-8?B?xaBrcmFiZWM=?= <jernej.skrabec@gmail.com>
To:     Alessandro Zummo <a.zummo@towertech.it>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Chen-Yu Tsai <wens@csie.org>,
        Samuel Holland <samuel@sholland.org>
Cc:     linux-arm-kernel@lists.infradead.org, linux-rtc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-sunxi@lists.linux.dev
Subject: Re: [PATCH 1/2] rtc: sun6i: Prevent an out-of-bounds read
Date:   Sun, 08 Jan 2023 20:39:27 +0100
Message-ID: <4834080.31r3eYUQgx@jernej-laptop>
In-Reply-To: <5c20af59-5fb5-8f7d-f6af-2b3984d79595@sholland.org>
References: <20221229184011.62925-1-samuel@sholland.org>
 <8201852.NyiUUSuA9g@jernej-laptop>
 <5c20af59-5fb5-8f7d-f6af-2b3984d79595@sholland.org>
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Dne sobota, 07. januar 2023 ob 18:15:47 CET je Samuel Holland napisal(a):
> Hi Jernej,
>=20
> On 1/5/23 11:26, Jernej =C5=A0krabec wrote:
> > Dne =C4=8Detrtek, 29. december 2022 ob 19:40:10 CET je Samuel Holland=20
napisal(a):
> >> If there is more than one parent clock in the devicetree, the
> >> driver sets .num_parents to a larger value than the number of array
> >> elements, which causes an out-of-bounds read in the clock framework.
> >=20
> > Is there any DT with more than one parent? I think more fixes are needed
> > if
> > this is the case.
>=20
> H616 and newer expect more than one parent, to accurately represent the
> RTC clock tree, but they use the CCU driver instead of this code.

If I understand that correctly, second clock would be 24 MHz crystal? In an=
y=20
case, if multiple parents are possible, check needs to be added to see if=20
parent clocks include 32 kHz clock or not.

>=20
> This bug is preventing us from relaxing `maxItems` in the binding for H6
> and older SoCs, even if Linux does not use the additional parent clocks.
> I want to fix this bug now, to give us the option (if beneficial) of
> relaxing the binding in the long-term future.

I wouldn't call it a bug, since it works just fine for currently defined=20
binding. Do you have DT binding change in pipeline?

Best regards,
Jernej

>=20
> Regards,
> Samuel
>=20
> >> Fix this by coercing the parent count to a Boolean value, like the
> >> driver expects.
> >>=20
> >> Fixes: 3855c2c3e546 ("rtc: sun6i: Expose the 32kHz oscillator")
> >> Signed-off-by: Samuel Holland <samuel@sholland.org>
> >> ---
> >>=20
> >>  drivers/rtc/rtc-sun6i.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>=20
> >> diff --git a/drivers/rtc/rtc-sun6i.c b/drivers/rtc/rtc-sun6i.c
> >> index ed5516089e9a..a22358a44e32 100644
> >> --- a/drivers/rtc/rtc-sun6i.c
> >> +++ b/drivers/rtc/rtc-sun6i.c
> >> @@ -294,7 +294,7 @@ static void __init sun6i_rtc_clk_init(struct
> >> device_node *node,
> >>=20
> >>  	init.parent_names =3D parents;
> >>  	/* ... number of clock parents will be 1. */
> >>=20
> >> -	init.num_parents =3D of_clk_get_parent_count(node) + 1;
> >> +	init.num_parents =3D !!of_clk_get_parent_count(node) + 1;
> >>=20
> >>  	of_property_read_string_index(node, "clock-output-names", 0,
> >>  =09
> >>  				      &init.name);