linux-kernel - Re: staging: r8188eu: struct rt_firmware

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Date:   Wed, 13 Apr 2022 23:58:51 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     Michael Straube <straube.linux@...il.com>,
        Larry Finger <Larry.Finger@...inger.net>
Cc:     Phillip Potter <phil@...lpotter.co.uk>,
        Greg KH <gregkh@...uxfoundation.org>,
        "open list:STAGING SUBSYSTEM" <linux-staging@...ts.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: staging: r8188eu: struct rt_firmware_header issues

Hi Michael,

On 4/13/22 19:27, Michael Straube wrote:
> Hi all,
> 
> I think the rt_firmware_hdr structure in rtw_fw.c has some issues.
> 
> 
> struct rt_firmware_hdr {
> 	/*  8-byte alinment required */
> 	/*  LONG WORD 0 ---- */
> 	__le16		Signature;	/* 92C0: test chip; 92C,
> 					 * 88C0: test chip; 88C1: MP A-cut;
> 					 * 92C1: MP A-cut */
> 	u8		Category;	/*  AP/NIC and USB/PCI */
> 	u8		Function;	/*  Reserved for different FW function
> 					 *  indcation, for further use when
> 					 *  driver needs to download different
> 					 *  FW for different conditions */
> 	__le16		Version;	/*  FW Version */
> 	u8		Subversion;	/*  FW Subversion, default 0x00 */
> 	u16		Rsvd1;
> 
> 	/*  LONG WORD 1 ---- */
> 	u8		Month;	/*  Release time Month field */
> 	u8		Date;	/*  Release time Date field */
> 	u8		Hour;	/*  Release time Hour field */
> 	u8		Minute;	/*  Release time Minute field */
> 	__le16		RamCodeSize;	/*  The size of RAM code */
> 	u8		Foundry;
> 	u8		Rsvd2;
> 
> 	/*  LONG WORD 2 ---- */
> 	__le32		SvnIdx;	/*  The SVN entry index */
> 	u32		Rsvd3;
> 
> 	/*  LONG WORD 3 ---- */
> 	u32		Rsvd4;
> 	u32		Rsvd5;
> };
> 
> 
> Then we have in rtl8188e_firmware_download():
> 
> 
> 	fwhdr = (struct rt_firmware_hdr *)dvobj->firmware.data;
> 
> 	<snip>
> 
> 	if (IS_FW_HEADER_EXIST(fwhdr)) {
> 		/*  Shift 32 bytes for FW header */
> 		fw_data = fw_data + 32;
> 		fw_size = fw_size - 32;
> 	}
> 
> We add/sub 32 bytes but the size of struct rt_firmware_hdr is actually
> 33 bytes. I noticed this when I wanted to replace:
> 

Looks like size of that structure is 36

└──$ pahole -C rt_firmware_hdr r8188eu.ko
struct rt_firmware_hdr {
	__le16                     Signature;            /*     0     2 */
	u8                         Category;             /*     2     1 */
	u8                         Function;             /*     3     1 */
	__le16                     Version;              /*     4     2 */
  	u8                         Subversion;           /*     6     1 */

  	/* XXX 1 byte hole, try to pack */

  	u16                        Rsvd1;                /*     8     2 */
  	u8                         Month;                /*    10     1 */
  	u8                         Date;                 /*    11     1 */
  	u8                         Hour;                 /*    12     1 */
  	u8                         Minute;               /*    13     1 */
  	__le16                     RamCodeSize;          /*    14     2 */
  	u8                         Foundry;              /*    16     1 */
  	u8                         Rsvd2;                /*    17     1 */

  	/* XXX 2 bytes hole, try to pack */

  	__le32                     SvnIdx;               /*    20     4 */
  	u32                        Rsvd3;                /*    24     4 */
  	u32                        Rsvd4;                /*    28     4 */
  	u32                        Rsvd5;                /*    32     4 */

  	/* size: 36, cachelines: 1, members: 17 */
  	/* sum members: 33, holes: 2, sum holes: 3 */
  	/* last cacheline: 36 bytes */
  };


And these comments like 'LONG WORD 1' looks misleading, maybe worth 
removing.


> 		fw_data = fw_data + 32;
> 		fw_size = fw_size - 32;
> 
> with:
> 		fw_data = fw_data + sizeof(struct rt_firmware_hdr);
> 		fw_size = fw_size - sizeof(struct rt_firmware_hdr);;
> 
> To me it looks add/sub 32 is correct here but the struct is
> wrong. I don't know if the firmware for this driver is so much different
> from firmware for the drivers in drivers/net/wireless/realtek/rtlwifi.
> They use a struct of size 32.
> 

I am not sure about 32... Why non-packed structures are passed via 
wires? Maybe `__packed` is missing? Is realtek fw open-source?

Just thoughts.

> Also, souldn't the u16 and u32 variables in the struct be __le16 and
> __le32 ?
> 
> I wonder if we can just use the rtlwifi_firmware_header structure from
> drivers/net/wireless/realtek/rtlwifi/wifi.h ?
> 

We _should_ use it, since its size is indeed 32 bytes.

└──$ pahole -s vmlinux | rg rtlwifi_firmware_header
rtlwifi_firmware_header	32	0


Looks like you have found a real bug


With regards,
Pavel Skripkin