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Date:   Wed, 22 May 2019 18:54:15 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Amitkumar Karwar <amitkarwar@...il.com>,
        Siva Rebbagondla <siva8118@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless@...r.kernel.org, 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 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
> > <natechancellor@...il.com> wrote:
> > >
> > > When building with -Wuninitialized, Clang warns:
> > >
> > > drivers/net/wireless/rsi/rsi_91x_sdio.c:940:43: warning: variable 'data'
> > > is uninitialized when used here [-Wuninitialized]
> > >         put_unaligned_le32(TA_HOLD_THREAD_VALUE, data);
> > >                                                  ^~~~
> > > drivers/net/wireless/rsi/rsi_91x_sdio.c:930:10: note: initialize the
> > > variable 'data' to silence this warning
> > >         u8 *data;
> > >                 ^
> > >                  = NULL
> > > 1 warning generated.
> > >
> > > Using Clang's suggestion of initializing data to NULL wouldn't work out
> > > because data will be dereferenced by put_unaligned_le32. Use kzalloc to
> > > properly initialize data, which matches a couple of other places in this
> > > driver.
> > >
> > > Fixes: e5a1ecc97e5f ("rsi: add firmware loading for 9116 device")
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/464
> > > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> > > ---
> > >  drivers/net/wireless/rsi/rsi_91x_sdio.c | 21 ++++++++++++++-------
> > >  1 file changed, 14 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/net/wireless/rsi/rsi_91x_sdio.c b/drivers/net/wireless/rsi/rsi_91x_sdio.c
> > > index f9c67ed473d1..b35728564c7b 100644
> > > --- a/drivers/net/wireless/rsi/rsi_91x_sdio.c
> > > +++ b/drivers/net/wireless/rsi/rsi_91x_sdio.c
> > > @@ -929,11 +929,15 @@ static int rsi_sdio_ta_reset(struct rsi_hw *adapter)
> > >         u32 addr;
> > >         u8 *data;
> > >
> > > +       data = kzalloc(sizeof(u32), GFP_KERNEL);
> > 
> > Something fishy is going on here.  We allocate 4 B but declare data as
> > a u8* (pointer to individual bytes)?  In general, dynamically
> > allocating that few bytes is a code smell; either you meant to just
> > use the stack, or this memory's lifetime extends past the lifetime of
> > this stackframe, at which point you probably just meant to stack
> > allocate space in a higher parent frame and pass this preallocated
> > memory down to the child frame to get filled in.
> > 
> > Reading through this code, I don't think that the memory is meant to
> > outlive the stack frame.  Is there a reason why we can't just declare
> > data as:
> > 
> > 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,
> @@ -947,7 +947,7 @@ static int rsi_sdio_ta_reset(struct rsi_hw *adapter)
>                 return status;
>         }
>  
> -       put_unaligned_le32(TA_SOFT_RST_CLR, data);
> +       put_unaligned_le32(TA_SOFT_RST_CLR, &data);
>         addr = TA_SOFT_RESET_REG | RSI_SD_REQUEST_MASTER;
>         status = rsi_sdio_write_register_multiple(adapter, addr,
>                                                   (u8 *)&data,
> @@ -957,7 +957,7 @@ static int rsi_sdio_ta_reset(struct rsi_hw *adapter)
>                 return status;
>         }
>  
> -       put_unaligned_le32(TA_PC_ZERO, data);
> +       put_unaligned_le32(TA_PC_ZERO, &data);
>         addr = TA_TH0_PC_REG | RSI_SD_REQUEST_MASTER;
>         status = rsi_sdio_write_register_multiple(adapter, addr,
>                                                   (u8 *)&data,
> @@ -967,7 +967,7 @@ static int rsi_sdio_ta_reset(struct rsi_hw *adapter)
>                 return -EINVAL;
>         }
>  
> -       put_unaligned_le32(TA_RELEASE_THREAD_VALUE, data);
> +       put_unaligned_le32(TA_RELEASE_THREAD_VALUE, &data);
>         addr = TA_RELEASE_THREAD_REG | RSI_SD_REQUEST_MASTER;
>         status = rsi_sdio_write_register_multiple(adapter, addr,
>                                                   (u8 *)&data,
> 
> 
> > 
> > then use ARRAY_SIZE(data) or RSI_9116_REG_SIZE in rsi_reset_chip(),
> > getting rid of the kzalloc/kfree?
> > 
> > (Sorry, I hate when a simple fixup becomes a "hey let's rewrite all
> > this code" thus becoming "that guy.")
> 
> If we aren't actually improving the code, then why bother? :)
> 
> Thank you for the review!
> Nathan
> 
> > -- 
> > Thanks,
> > ~Nick Desaulniers

Hi all,

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.

Thanks,
Nathan

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