Re: [PATCH] wifi: iwlegacy: Fix "field-spanning write" warning in il_enqueue_hcmd()

[Stanislaw Gruszka <stf_xl@wp.pl>]

On Thu, Sep 12, 2024 at 01:01:21AM +0200, Ben Hutchings wrote:
> iwlegacy uses command buffers with a payload size of 320
> bytes (default) or 4092 bytes (huge).  The struct il_device_cmd type
> describes the default buffers and there is no separate type describing
> the huge buffers.
> 
> The il_enqueue_hcmd() function works with both default and huge
> buffers, and has a memcpy() to the buffer payload.  The size of
> this copy may exceed 320 bytes when using a huge buffer, which
> now results in a run-time warning:
> 
>     memcpy: detected field-spanning write (size 1014) of single field "&out_cmd->cmd.payload" at drivers/net/wireless/intel/iwlegacy/common.c:3170 (size 320)
> 
> To fix this:
> 
> - Define a new struct type for huge buffers, with a correctly sized
>   payload field
> - When using a huge buffer in il_enqueue_hcmd(), cast the command
>   buffer pointer to that type when looking up the payload field
> 
> Reported-by: Martin-Éric Racine <martin-eric.racine@iki.fi>
> References: https://bugs.debian.org/1062421
> References: https://bugzilla.kernel.org/show_bug.cgi?id=219124
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> Fixes: 54d9469bc515 ("fortify: Add run-time WARN for cross-field memcpy()")
> Tested-by: Martin-Éric Racine <martin-eric.racine@iki.fi>
> Tested-by: Brandon Nielsen <nielsenb@jetfuse.net>

I proposed diffrent fix for this here:
https://lore.kernel.org/linux-wireless/20240520073210.GA693073@wp.pl/
but never get feedback if it works on real HW.
So I prefer this one, sice it was tested.

Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>

Martin-Éric and Brandon, could you plase also test patch from 
https://lore.kernel.org/linux-wireless/Zr2gxERA3RL3EwRe@elsanto/
if it does not break the driver?

Thanks
Stanislaw

> ---
>  drivers/net/wireless/intel/iwlegacy/common.c | 13 ++++++++++++-
>  drivers/net/wireless/intel/iwlegacy/common.h | 12 ++++++++++++
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlegacy/common.c b/drivers/net/wireless/intel/iwlegacy/common.c
> index 9d33a66a49b5..4616293ec0cf 100644
> --- a/drivers/net/wireless/intel/iwlegacy/common.c
> +++ b/drivers/net/wireless/intel/iwlegacy/common.c
> @@ -3122,6 +3122,7 @@ il_enqueue_hcmd(struct il_priv *il, struct il_host_cmd *cmd)
>  	struct il_cmd_meta *out_meta;
>  	dma_addr_t phys_addr;
>  	unsigned long flags;
> +	u8 *out_payload;
>  	u32 idx;
>  	u16 fix_size;
>  
> @@ -3157,6 +3158,16 @@ il_enqueue_hcmd(struct il_priv *il, struct il_host_cmd *cmd)
>  	out_cmd = txq->cmd[idx];
>  	out_meta = &txq->meta[idx];
>  
> +	/* The payload is in the same place in regular and huge
> +	 * command buffers, but we need to let the compiler know when
> +	 * we're using a larger payload buffer to avoid "field-
> +	 * spanning write" warnings at run-time for huge commands.
> +	 */
> +	if (cmd->flags & CMD_SIZE_HUGE)
> +		out_payload = ((struct il_device_cmd_huge *)out_cmd)->cmd.payload;
> +	else
> +		out_payload = out_cmd->cmd.payload;
> +
>  	if (WARN_ON(out_meta->flags & CMD_MAPPED)) {
>  		spin_unlock_irqrestore(&il->hcmd_lock, flags);
>  		return -ENOSPC;
> @@ -3170,7 +3181,7 @@ il_enqueue_hcmd(struct il_priv *il, struct il_host_cmd *cmd)
>  		out_meta->callback = cmd->callback;
>  
>  	out_cmd->hdr.cmd = cmd->id;
> -	memcpy(&out_cmd->cmd.payload, cmd->data, cmd->len);
> +	memcpy(out_payload, cmd->data, cmd->len);
>  
>  	/* At this point, the out_cmd now has all of the incoming cmd
>  	 * information */
> diff --git a/drivers/net/wireless/intel/iwlegacy/common.h b/drivers/net/wireless/intel/iwlegacy/common.h
> index 69687fcf963f..027dae5619a3 100644
> --- a/drivers/net/wireless/intel/iwlegacy/common.h
> +++ b/drivers/net/wireless/intel/iwlegacy/common.h
> @@ -560,6 +560,18 @@ struct il_device_cmd {
>  
>  #define TFD_MAX_PAYLOAD_SIZE (sizeof(struct il_device_cmd))
>  
> +/**
> + * struct il_device_cmd_huge
> + *
> + * For use when sending huge commands.
> + */
> +struct il_device_cmd_huge {
> +	struct il_cmd_header hdr;	/* uCode API */
> +	union {
> +		u8 payload[IL_MAX_CMD_SIZE - sizeof(struct il_cmd_header)];
> +	} __packed cmd;
> +} __packed;
> +
>  struct il_host_cmd {
>  	const void *data;
>  	unsigned long reply_page;