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

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Message-ID: <2a249d99-b1e7-7943-0ed4-d5529f7abc33@codeaurora.org>
Date:   Mon, 4 May 2020 08:33:34 -0600
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Bhaumik Bhatt <bbhatt@...eaurora.org>, mani@...nel.org
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        hemantk@...eaurora.org
Subject: Re: [PATCH v4 8/8] bus: mhi: core: Ensure non-zero session or
 sequence ID values are used

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@...eaurora.org>
> Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.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.

-- 
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.