linux-kernel - Re: [PATCH] rtw89: Fix crash by loading compressed firmware file

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Date:   Fri, 5 Nov 2021 14:28:39 +0000
From:   Pkshih <pkshih@...ltek.com>
To:     "kvalo@...eaurora.org" <kvalo@...eaurora.org>,
        "tiwai@...e.de" <tiwai@...e.de>
CC:     "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "Larry.Finger@...il.com" <Larry.Finger@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rtw89: Fix crash by loading compressed firmware file

On Fri, 2021-11-05 at 11:03 +0200, Kalle Valo wrote:
> Takashi Iwai <tiwai@...e.de> writes:
> 
> > On Fri, 05 Nov 2021 09:25:13 +0100,
> > Kalle Valo wrote:
> > > Takashi Iwai <tiwai@...e.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.
> 


I can use a struct to access firmware header, becuase their fields
are multiple of 8 bits.

But, the "firmware section header" that is additional header followed
by firmware header, and it contains bit fields, likes:

#define GET_FWSECTION_HDR_SEC_SIZE(fwhdr)	\
	le32_get_bits(*((__le32 *)(fwhdr) + 1), GENMASK(23, 0))
#define GET_FWSECTION_HDR_CHECKSUM(fwhdr)	\
	le32_get_bits(*((__le32 *)(fwhdr) + 1), BIT(28))
#define GET_FWSECTION_HDR_REDL(fwhdr)	\
	le32_get_bits(*((__le32 *)(fwhdr) + 1), BIT(29))
#define GET_FWSECTION_HDR_DL_ADDR(fwhdr)	\
	le32_get_bits(*((__le32 *)(fwhdr)), GENMASK(31, 0))

If we use a struct, it needs big-/little- endians parts.

Then, we will access firmware header with two methods; is
it reasonable?


The macro SET_FW_HDR_PART_SIZE() is used to set the firmware
partition size we are going to download, and it is only used
by rtw89_fw_download_hdr(). So, I will set the partition size
after copying constant firmware header into skb->data.

--
Ping-Ke