linux-kernel - Re: [PATCH] drm/komeda: use bitmap API to convert U32 to bitmap

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Message-ID: <20201228195016.GD4077@smile.fi.intel.com>
Date:   Mon, 28 Dec 2020 21:50:16 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Carsten Haitzler <carsten.haitzler@....com>,
        Liviu Dudau <liviu.dudau@....com>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Subject: Re: [PATCH] drm/komeda: use bitmap API to convert U32 to bitmap

On Mon, Dec 28, 2020 at 11:43:43AM -0800, Yury Norov wrote:
> The commit be3e477effba636ad25 ("drm/komeda: Fix bit
> check to import to value of proper type") fixes possible
> out-of-bound issue related to find_first_bit() usage, but
> does not address the endianness problem.

Hmm... Can you elaborate?

...

>  				    u32 comp_mask)

> -	unsigned long comp_mask_local = (unsigned long)comp_mask;

Here we convert u32 to unsigned long (LSB is kept LSB since it happens in
native endianess).

> -	id = find_first_bit(&comp_mask_local, 32);

Here it takes an address to unsigned long and tries only lower 32 bits.

Are you telling that find_first_bit() has an issue?

-- 
With Best Regards,
Andy Shevchenko