Re: [PATCH v4 8/8] bus: mhi: core: Ensure non-zero session or sequence ID values are used

[bbhatt]

On 2020-05-04 07:33, Jeffrey Hugo wrote:
> On 5/1/2020 8:32 PM, Bhaumik Bhatt wrote:
> > While writing any sequence or session identifiers, it is possible that
> > the host could write a zero value, whereas only non-zero values should
> > be supported writes to those registers. Ensure that the host does not
> > write a non-zero value for them and also log them in debug messages.
> >
> > Suggested-by: Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx>
> > Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> > ---
> >   drivers/bus/mhi/core/boot.c     | 15 +++++++--------
> >   drivers/bus/mhi/core/internal.h |  1 +
> >   2 files changed, 8 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/bus/mhi/core/boot.c b/drivers/bus/mhi/core/boot.c
> > index e5fcde1..9fe9c59 100644
> > --- a/drivers/bus/mhi/core/boot.c
> > +++ b/drivers/bus/mhi/core/boot.c
> > @@ -43,10 +43,7 @@ void mhi_rddm_prepare(struct mhi_controller 
> > *mhi_cntrl,
> >   		      lower_32_bits(mhi_buf->dma_addr));
> >     	mhi_write_reg(mhi_cntrl, base, BHIE_RXVECSIZE_OFFS, 
> > mhi_buf->len);
> > -	sequence_id = prandom_u32() & BHIE_RXVECSTATUS_SEQNUM_BMSK;
> > -
> > -	if (unlikely(!sequence_id))
> > -		sequence_id = 1;
> > +	sequence_id = (MHI_RANDOM_U32_NONZERO & 
> > BHIE_RXVECSTATUS_SEQNUM_BMSK);
>
> I don't think this math works.  For example, if MHI_RANDOM_U32_NONZERO
> is 0x0FF0, and BHIE_RXVECSTATUS_SEQNUM_BMSK is 0xF, then sequence_id
> will end up being 0.

In this case, SEQNUM BMSK is set to 0x3FFFFFFF so this change will still 
work as
we only supplied a non-zero number macro to AND with the mask.
However, I agree that may not be the case always that we would know the 
bitmask
in advance so it is better to fix it for good.

Thanks for the catch! I have updated the change to have the macro take 
the
bitmask as a parameter and output a non-zero value.