Subject: Re: [PATCH] rsi: Properly initialize data in rsi_sdio_ta_reset

From: Nathan Chancellor <[email-masked]>
Date: Thu, 2 May 2019 20:17:18 -0700

On Thu, May 02, 2019 at 11:18:01AM -0700, Nick Desaulniers wrote:
> On Thu, May 2, 2019 at 8:16 AM Nathan Chancellor
> <[email-masked]> 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 <[email-masked]>
> > ---
> >  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