linux-kernel - Re: [PATCH 1/2] OPP: add index check to assert to avoid buffer overflow in _read

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Message-ID: <20241129090457.4ibsyulffydnc3ns@vireshk-i7>
Date: Fri, 29 Nov 2024 14:34:57 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Neil Armstrong <neil.armstrong@...aro.org>
Cc: Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
	Stephen Boyd <sboyd@...nel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] OPP: add index check to assert to avoid buffer
 overflow in _read_freq()

On 29-11-24, 09:53, Neil Armstrong wrote:
> Hi,
> 
> On 29/11/2024 09:40, Viresh Kumar wrote:
> > On 28-11-24, 11:07, Neil Armstrong wrote:
> > > Pass the freq index to the assert function to make sure
> > > we do not read a freq out of the opp->rates[] table.
> > > 
> > > Without that the index value is never checked when called from
> > > dev_pm_opp_find_freq_exact_indexed() or
> > > dev_pm_opp_find_freq_ceil/floor_indexed().
> > 
> > These APIs aren't supported for cases where we have more than one clks
> > available and hence assert for single clk.
> > 
> 
> I don't understand, the _indexed functions clearly have an index parameter
> which is documented as "Clock index"

Ahh, I missed that there are few _indexed() helpers as well which you are
correctly modifying.

> I agree we could leave the other ones with assert_single_clk, but we would
> need to duplicate it to have one with the index parameter, so it felt simpler
> to use assert_clk_index everywhere but indeed we do not exclude them for
> when there's multiple clock...

What prevents a user to call dev_pm_opp_find_freq_exact() for a multi-clk setup
after your patch ? As we use Index = 0 here in the code.

That's why I would prefer the earlier assert for all these, except the indexed
ones.

-- 
viresh