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Date:   Tue, 19 May 2020 03:37:37 +0000
From:   Qiang Zhao <qiang.zhao@....com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Leo Li <leoyang.li@....com>
CC:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Kees Cook <keescook@...omium.org>
Subject: RE: [PATCH] soc: fsl: qe: Replace one-element array and use
 struct_size() helper


On 2020/5/19 6:19, Gustavo A. R. Silva <gustavoars@...nel.org> wrote:

> -----Original Message-----
> From: Gustavo A. R. Silva <gustavoars@...nel.org>
> Sent: 2020年5月19日 6:19
> To: Qiang Zhao <qiang.zhao@....com>; Leo Li <leoyang.li@....com>
> Cc: linuxppc-dev@...ts.ozlabs.org; linux-arm-kernel@...ts.infradead.org;
> linux-kernel@...r.kernel.org; Gustavo A. R. Silva <gustavo@...eddedor.com>;
> Kees Cook <keescook@...omium.org>
> Subject: [PATCH] soc: fsl: qe: Replace one-element array and use struct_size()
> helper
> 
> The current codebase makes use of one-element arrays in the following
> form:
> 
> struct something {
>     int length;
>     u8 data[1];
> };
> 
> struct something *instance;
> 
> instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
> instance->length = size;
> memcpy(instance->data, source, size);
> 
> but the preferred mechanism to declare variable-length types such as these
> ones is a flexible array member[1][2], introduced in C99:
> 
> struct foo {
>         int stuff;
>         struct boo array[];
> };
> 
> By making use of the mechanism above, we will get a compiler warning in case
> the flexible array does not occur last in the structure, which will help us prevent
> some kind of undefined behavior bugs from being inadvertently introduced[3]
> to the codebase from now on. So, replace the one-element array with a
> flexible-array member.
> 
> Also, make use of the new struct_size() helper to properly calculate the size of
> struct qe_firmware.
> 
> This issue was found with the help of Coccinelle and, audited and fixed
> _manually_.
> 
> [1]
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.
> org%2Fonlinedocs%2Fgcc%2FZero-Length.html&amp;data=02%7C01%7Cqiang.
> zhao%40nxp.com%7Cb058bcb9af134df8446808d7fb78cfa9%7C686ea1d3bc2b
> 4c6fa92cd99c5c301635%7C0%7C0%7C637254368610203908&amp;sdata=70
> a6VBg3oWQf9a5KICuCEuIj6gw57NKYhNv2JL8JdDY%3D&amp;reserved=0
> [2]
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.c
> om%2FKSPP%2Flinux%2Fissues%2F21&amp;data=02%7C01%7Cqiang.zhao%40
> nxp.com%7Cb058bcb9af134df8446808d7fb78cfa9%7C686ea1d3bc2b4c6fa92c
> d99c5c301635%7C0%7C0%7C637254368610213901&amp;sdata=kVyNBYHbm
> a5jCO9pbkoHMetHEYGvWDq6Xw%2BBeC7uHII%3D&amp;reserved=0
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  drivers/soc/fsl/qe/qe.c | 4 ++--
>  include/soc/fsl/qe/qe.h | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/soc/fsl/qe/qe.c b/drivers/soc/fsl/qe/qe.c index
> 447146861c2c1..2df20d6f85fa4 100644
> --- a/drivers/soc/fsl/qe/qe.c
> +++ b/drivers/soc/fsl/qe/qe.c
> @@ -448,7 +448,7 @@ int qe_upload_firmware(const struct qe_firmware
> *firmware)
>  	unsigned int i;
>  	unsigned int j;
>  	u32 crc;
> -	size_t calc_size = sizeof(struct qe_firmware);
> +	size_t calc_size;
>  	size_t length;
>  	const struct qe_header *hdr;
> 
> @@ -480,7 +480,7 @@ int qe_upload_firmware(const struct qe_firmware
> *firmware)
>  	}
> 
>  	/* Validate the length and check if there's a CRC */
> -	calc_size += (firmware->count - 1) * sizeof(struct qe_microcode);
> +	calc_size = struct_size(firmware, microcode, firmware->count);
> 
>  	for (i = 0; i < firmware->count; i++)
>  		/*
> diff --git a/include/soc/fsl/qe/qe.h b/include/soc/fsl/qe/qe.h index
> e282ac01ec081..3feddfec9f87d 100644
> --- a/include/soc/fsl/qe/qe.h
> +++ b/include/soc/fsl/qe/qe.h
> @@ -307,7 +307,7 @@ struct qe_firmware {
>  		u8 revision;		/* The microcode version revision */
>  		u8 padding;		/* Reserved, for alignment */
>  		u8 reserved[4];		/* Reserved, for future expansion */
> -	} __attribute__ ((packed)) microcode[1];
> +	} __packed microcode[];
>  	/* All microcode binaries should be located here */
>  	/* CRC32 should be located here, after the microcode binaries */  }
> __attribute__ ((packed));
> --
> 2.26.2
[>] 

Reviewed-by: Qiang Zhao <qiang.zhao@....com>

Best Regards
Qiang Zhao

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