linux-kernel - RE: [PATCH v2] mei: Avoid the use of one-element arrays

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Message-ID: <071940a8c76c4652b4fd58195719c471@intel.com>
Date:   Wed, 22 Jul 2020 22:40:05 +0000
From:   "Winkler, Tomas" <tomas.winkler@...el.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>
Subject: RE: [PATCH v2] mei: Avoid the use of one-element arrays

> 
> Hi Tomas,
> 
> Please, see my comments below...
> 
> On 7/22/20 14:04, Winkler, Tomas wrote:
> >
> >>
> >> Hi all,
> >>
> >> Friendly ping: who can take this? :)
> >>
> >> Thanks
> >> --
> >> Gustavo
> >>
> >> On 7/14/20 16:45, Gustavo A. R. Silva wrote:
> >>> One-element arrays are being deprecated[1]. Replace the one-element
> >>> arrays with a simple value type u8 reserved, once this is just a
> >>> placeholder for alignment.
> >>>
> >>> Also, while there, use the preferred form for passing a size of a struct.
> >>> The alternative form where struct name is spelled out hurts
> >>> readability and introduces an opportunity for a bug when the
> >>> variable type is changed but the corresponding sizeof that is passed
> >>> as argument is
> >> not.
> >>>
> >>> [1] https://github.com/KSPP/linux/issues/79
> >>>
> >>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> >>> ---
> >>> Changes in v2:
> >>>  - Use a more concise changelog text.
> >>>
> >>>  drivers/misc/mei/hbm.c | 4 ++--
> >>>  drivers/misc/mei/hw.h  | 6 +++---
> >>>  2 files changed, 5 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/drivers/misc/mei/hbm.c b/drivers/misc/mei/hbm.c index
> >>> a44094cdbc36..f020d5594154 100644
> >>> --- a/drivers/misc/mei/hbm.c
> >>> +++ b/drivers/misc/mei/hbm.c
> >>> @@ -408,14 +408,14 @@ static int mei_hbm_add_cl_resp(struct
> >>> mei_device *dev, u8 addr, u8 status)  {
> >>>  	struct mei_msg_hdr mei_hdr;
> >>>  	struct hbm_add_client_response resp;
> >>> -	const size_t len = sizeof(struct hbm_add_client_response);
> >>> +	const size_t len = sizeof(resp);
> >>>  	int ret;
> >>>
> >>>  	dev_dbg(dev->dev, "adding client response\n");
> >>>
> >>>  	mei_hbm_hdr(&mei_hdr, len);
> >>>
> >>> -	memset(&resp, 0, sizeof(struct hbm_add_client_response));
> >>> +	memset(&resp, 0, len);
> >>>  	resp.hbm_cmd = MEI_HBM_ADD_CLIENT_RES_CMD;
> >>>  	resp.me_addr = addr;
> >>>  	resp.status  = status;
> >
> > This should be probably in a different patch it's not related to the second
> part.


Frankly I will post other version of this that cleans the whole file. 

> >
> >>> diff --git a/drivers/misc/mei/hw.h b/drivers/misc/mei/hw.h index
> >>> b1a8d5ec88b3..8c0297f0e7f3 100644
> >>> --- a/drivers/misc/mei/hw.h
> >>> +++ b/drivers/misc/mei/hw.h
> > I have second thoughts of this part as all reserved fields in this
> > file are of form u8 reserved[X], so we will lose that uniformity with
> > this change, you have to look at the file as whole not just at the patch.  So I
> prefer we drop that part of the patch.
> >
> 
> This is actually the main point of this patch: the removal of one-element
> arrays.
> And yeah, every place in the kernel that uses the form that you mention will
> see it's uniformity slightly modified, and that's for a good cause: the removal
> of one-element arrays, so we can enable bounds checking.

I was going over https://github.com/KSPP/linux/issues/79, I'm not sure this all related  to flexible arrays,
those are just reserved struct members. So because it's hard to identify a legitimate usage of single element arrays
we are going to kill them all? It's more esthetic / readability issue here but there might be some legit use case for one element array, no?


> 
> Thanks
> --
> Gustavo
> 
> >>> @@ -346,13 +346,13 @@ struct hbm_add_client_request {
> >>>   * @hbm_cmd: bus message command header
> >>>   * @me_addr: address of the client in ME
> >>>   * @status: if HBMS_SUCCESS then the client can now accept
> connections.
> >>> - * @reserved: reserved
> >>> + * @reserved: reserved for alignment.
> >>>   */
> >>>  struct hbm_add_client_response {
> >>>  	u8 hbm_cmd;
> >>>  	u8 me_addr;
> >>>  	u8 status;
> >>> -	u8 reserved[1];
> >>> +	u8 reserved;
> >>>  } __packed;
> >>>
> >>>  /**
> >>> @@ -461,7 +461,7 @@ struct hbm_notification {
> >>>  	u8 hbm_cmd;
> >>>  	u8 me_addr;
> >>>  	u8 host_addr;
> >>> -	u8 reserved[1];
> >>> +	u8 reserved;
> >>>  } __packed;
> >>>
> >>>  /**
> >>>