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

[Brandon Nielsen <nielsenb@xxxxxxxxxxx>]

On 9/12/24 3:39 AM, Stanislaw Gruszka wrote:
> 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@xxxxxx>
> > References: https://bugs.debian.org/1062421
> > References: https://bugzilla.kernel.org/show_bug.cgi?id=219124
> > Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
> > Fixes: 54d9469bc515 ("fortify: Add run-time WARN for cross-field memcpy()")
> > Tested-by: Martin-Éric Racine <martin-eric.racine@xxxxxx>
> > Tested-by: Brandon Nielsen <nielsenb@xxxxxxxxxxx>
>
> I proposed diffrent fix for this here:
> https://lore.kernel.org/linux-wireless/20240520073210.GA693073@xxxxx/
> 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@xxxxx>
>
> 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?

As far as I can tell nothing breaks with that additional patch applied.

> 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;