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From:   Kalle Valo <kvalo@codeaurora.org>
To:     Takashi Iwai <tiwai@suse.de>
Cc:     Ping-Ke Shih <pkshih@realtek.com>, linux-wireless@vger.kernel.org,
        linux-kernel@vger.kernel.org, Larry Finger <Larry.Finger@gmail.com>
Subject: Re: [PATCH] rtw89: Fix crash by loading compressed firmware file
References: <20211105071725.31539-1-tiwai@suse.de>
        <s5hpmrfgj93.wl-tiwai@suse.de> <87zgqjqaae.fsf@codeaurora.org>
        <s5hh7crgflg.wl-tiwai@suse.de>
Date:   Fri, 05 Nov 2021 11:03:55 +0200
In-Reply-To: <s5hh7crgflg.wl-tiwai@suse.de> (Takashi Iwai's message of "Fri,
        05 Nov 2021 09:40:43 +0100")
Message-ID: <87v917q8hw.fsf@codeaurora.org>
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Takashi Iwai <tiwai@suse.de> writes:

> On Fri, 05 Nov 2021 09:25:13 +0100,
> Kalle Valo wrote:
>> 
>> Takashi Iwai <tiwai@suse.de> writes:
>> 
>> > On Fri, 05 Nov 2021 08:17:25 +0100,
>> > Takashi Iwai wrote:
>> >> 
>> >> When a firmware is loaded in the compressed format or via user-mode
>> >> helper, it's mapped in read-only, and the rtw89 driver crashes at
>> >> rtw89_fw_download() when it tries to modify some data.
>> >> 
>> >> This patch is an attemp to avoid the crash by re-allocating the data
>> >> via vmalloc() for the data modification.
>> >
>> > Alternatively, we may drop the code that modifies the loaded firmware
>> > data?  At least SET_FW_HDR_PART_SIZE() in rtw89_fw_hdr_parser() looks
>> > writing it, and I have no idea why this overwrite is needed.
>> 
>> Strange, isn't the firmware data marked as const just to avoid this kind
>> of problem? Does rtw89 have wrong casts somewhere which removes the
>> const?
>
> Yes.  SET_FW_HDR_PART_SIZE() does the cast, dropping the const.

Oh man, all of GET and SET macros in fw.h have those casts:

#define GET_FW_HDR_MAJOR_VERSION(fwhdr)	\
	le32_get_bits(*((__le32 *)(fwhdr) + 1), GENMASK(7, 0))
#define GET_FW_HDR_MINOR_VERSION(fwhdr)	\
	le32_get_bits(*((__le32 *)(fwhdr) + 1), GENMASK(15, 8))
#define GET_FW_HDR_SUBVERSION(fwhdr)	\
	le32_get_bits(*((__le32 *)(fwhdr) + 1), GENMASK(23, 16))

I don't know how I missed those during my review :( But this is exactly
why I prefer having a proper struct for commands and events, instead of
u8 buf used with these macros.

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