Re: [PATCH][next] ath11k: Replace one-element array with flexible-array member
From: Gustavo A. R. Silva
Date: Sun Sep 12 2021 - 15:40:32 EST
Hi Kalle,
I wonder if you can take this patch, please.
Thanks
--
Gustavo
On 8/23/21 12:21, Gustavo A. R. Silva wrote:
> There is a regular need in the kernel to provide a way to declare having a
> dynamically sized set of trailing elements in a structure. Kernel code
> should always use "flexible array members"[1] for these cases. The older
> style of one-element or zero-length arrays should no longer be used[2].
>
> Refactor the code a bit according to the use of a flexible-array member in
> struct scan_chan_list_params instead of a one-element array, and use the
> struct_size() helper.
>
> Also, save 25 (too many) bytes that were being allocated:
>
> $ pahole -C channel_param drivers/net/wireless/ath/ath11k/reg.o
> struct channel_param {
> u8 chan_id; /* 0 1 */
> u8 pwr; /* 1 1 */
> u32 mhz; /* 2 4 */
>
> /* Bitfield combined with next fields */
>
> u32 half_rate:1; /* 4:16 4 */
> u32 quarter_rate:1; /* 4:17 4 */
> u32 dfs_set:1; /* 4:18 4 */
> u32 dfs_set_cfreq2:1; /* 4:19 4 */
> u32 is_chan_passive:1; /* 4:20 4 */
> u32 allow_ht:1; /* 4:21 4 */
> u32 allow_vht:1; /* 4:22 4 */
> u32 allow_he:1; /* 4:23 4 */
> u32 set_agile:1; /* 4:24 4 */
> u32 psc_channel:1; /* 4:25 4 */
>
> /* XXX 6 bits hole, try to pack */
>
> u32 phy_mode; /* 8 4 */
> u32 cfreq1; /* 12 4 */
> u32 cfreq2; /* 16 4 */
> char maxpower; /* 20 1 */
> char minpower; /* 21 1 */
> char maxregpower; /* 22 1 */
> u8 antennamax; /* 23 1 */
> u8 reg_class_id; /* 24 1 */
>
> /* size: 25, cachelines: 1, members: 21 */
> /* sum members: 23 */
> /* sum bitfield members: 10 bits, bit holes: 1, sum bit holes: 6 bits */
> /* last cacheline: 25 bytes */
> } __attribute__((__packed__));
>
> as previously, sizeof(struct scan_chan_list_params) was 32 bytes:
>
> $ pahole -C scan_chan_list_params drivers/net/wireless/ath/ath11k/reg.o
> struct scan_chan_list_params {
> u32 pdev_id; /* 0 4 */
> u16 nallchans; /* 4 2 */
> struct channel_param ch_param[1]; /* 6 25 */
>
> /* size: 32, cachelines: 1, members: 3 */
> /* padding: 1 */
> /* last cacheline: 32 bytes */
> };
>
> and now with the flexible array transformation it is just 8 bytes:
>
> $ pahole -C scan_chan_list_params drivers/net/wireless/ath/ath11k/reg.o
> struct scan_chan_list_params {
> u32 pdev_id; /* 0 4 */
> u16 nallchans; /* 4 2 */
> struct channel_param ch_param[]; /* 6 0 */
>
> /* size: 8, cachelines: 1, members: 3 */
> /* padding: 2 */
> /* last cacheline: 8 bytes */
> };
>
> This helps with the ongoing efforts to globally enable -Warray-bounds and
> get us closer to being able to tighten the FORTIFY_SOURCE routines on
> memcpy().
>
> This issue was found with the help of Coccinelle and audited and fixed,
> manually.
>
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
>
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/109
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> ---
> drivers/net/wireless/ath/ath11k/reg.c | 7 ++-----
> drivers/net/wireless/ath/ath11k/wmi.c | 2 +-
> drivers/net/wireless/ath/ath11k/wmi.h | 2 +-
> 3 files changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/ath11k/reg.c b/drivers/net/wireless/ath/ath11k/reg.c
> index e1a1df169034..c83d265185f1 100644
> --- a/drivers/net/wireless/ath/ath11k/reg.c
> +++ b/drivers/net/wireless/ath/ath11k/reg.c
> @@ -97,7 +97,6 @@ int ath11k_reg_update_chan_list(struct ath11k *ar)
> struct channel_param *ch;
> enum nl80211_band band;
> int num_channels = 0;
> - int params_len;
> int i, ret;
>
> bands = hw->wiphy->bands;
> @@ -117,10 +116,8 @@ int ath11k_reg_update_chan_list(struct ath11k *ar)
> if (WARN_ON(!num_channels))
> return -EINVAL;
>
> - params_len = sizeof(struct scan_chan_list_params) +
> - num_channels * sizeof(struct channel_param);
> - params = kzalloc(params_len, GFP_KERNEL);
> -
> + params = kzalloc(struct_size(params, ch_param, num_channels),
> + GFP_KERNEL);
> if (!params)
> return -ENOMEM;
>
> diff --git a/drivers/net/wireless/ath/ath11k/wmi.c b/drivers/net/wireless/ath/ath11k/wmi.c
> index 6c253eae9d06..0a634ba04509 100644
> --- a/drivers/net/wireless/ath/ath11k/wmi.c
> +++ b/drivers/net/wireless/ath/ath11k/wmi.c
> @@ -2285,7 +2285,7 @@ int ath11k_wmi_send_scan_chan_list_cmd(struct ath11k *ar,
> u16 num_send_chans, num_sends = 0, max_chan_limit = 0;
> u32 *reg1, *reg2;
>
> - tchan_info = &chan_list->ch_param[0];
> + tchan_info = chan_list->ch_param;
> while (chan_list->nallchans) {
> len = sizeof(*cmd) + TLV_HDR_SIZE;
> max_chan_limit = (wmi->wmi_ab->max_msg_len[ar->pdev_idx] - len) /
> diff --git a/drivers/net/wireless/ath/ath11k/wmi.h b/drivers/net/wireless/ath/ath11k/wmi.h
> index d35c47e0b19d..d9c83726f65d 100644
> --- a/drivers/net/wireless/ath/ath11k/wmi.h
> +++ b/drivers/net/wireless/ath/ath11k/wmi.h
> @@ -3608,7 +3608,7 @@ struct wmi_stop_scan_cmd {
> struct scan_chan_list_params {
> u32 pdev_id;
> u16 nallchans;
> - struct channel_param ch_param[1];
> + struct channel_param ch_param[];
> };
>
> struct wmi_scan_chan_list_cmd {
>