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 <jh...@codeaurora.org>
Signed-off-by: Bhaumik Bhatt <bbh...@codeaurora.org>
---
  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.

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