netdev - Re: [PATCH] rsi: Properly initialize data in rsi_sdio_ta

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Date:   Thu, 23 May 2019 10:51:01 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Amitkumar Karwar <amitkarwar@...il.com>,
        Siva Rebbagondla <siva8118@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] rsi: Properly initialize data in rsi_sdio_ta_reset

On Thu, May 23, 2019 at 3:54 AM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> On Thu, May 02, 2019 at 08:17:18PM -0700, Nathan Chancellor wrote:
> > On Thu, May 02, 2019 at 11:18:01AM -0700, Nick Desaulniers wrote:
> > > On Thu, May 2, 2019 at 8:16 AM Nathan Chancellor
> > > u8 data [4];
> >
> > data was __le32 in rsi_reset_chip() before commit f700546682a6 ("rsi:
> > fix nommu_map_sg overflow kernel panic").
> >
> > I wonder if this would be okay for this function:
> >
> > -------------------------------------------------
> >
> > diff --git a/drivers/net/wireless/rsi/rsi_91x_sdio.c b/drivers/net/wireless/rsi/rsi_91x_sdio.c
> > index f9c67ed473d1..0330c50ab99c 100644
> > --- a/drivers/net/wireless/rsi/rsi_91x_sdio.c
> > +++ b/drivers/net/wireless/rsi/rsi_91x_sdio.c
> > @@ -927,7 +927,7 @@ static int rsi_sdio_ta_reset(struct rsi_hw *adapter)
> >  {
> >         int status;
> >         u32 addr;
> > -       u8 *data;
> > +       u8 data;
> >
> >         status = rsi_sdio_master_access_msword(adapter, TA_BASE_ADDR);
> >         if (status < 0) {
> > @@ -937,7 +937,7 @@ static int rsi_sdio_ta_reset(struct rsi_hw *adapter)
> >         }
> >
> >         rsi_dbg(INIT_ZONE, "%s: Bring TA out of reset\n", __func__);
> > -       put_unaligned_le32(TA_HOLD_THREAD_VALUE, data);
> > +       put_unaligned_le32(TA_HOLD_THREAD_VALUE, &data);
> >         addr = TA_HOLD_THREAD_REG | RSI_SD_REQUEST_MASTER;
> >         status = rsi_sdio_write_register_multiple(adapter, addr,
> >                                                   (u8 *)&data,

This is clearly not ok, as put_unaligned_le32() stores four bytes, and
the local variable is only one byte!

Also, sdio does use DMA for transfers, so the variable has to be
dynamically allocated. I think your original patch was correct.
The only change I'd possibly make would be to use
RSI_9116_REG_SIZE instead of sizeof(u32).

> Did any of the maintainers have any comments on what the correct
> solution is here to resolve this warning? It is one of the few left
> before we can turn on -Wuninitialized for the whole kernel.

I would argue that this should not stop us from turning it on, as the
warning is for a clear bug in the code that absolutely needs to be
fixed, rather than a false-positive.

       Arnd