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Message-ID: <27609135-af23-68b3-0c2c-b4f0c40963d0@quicinc.com>
Date:   Fri, 27 Oct 2023 08:19:44 -0600
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Subject: Re: [PATCH] bus: mhi: host: Add alignment check for event ring read
 pointer
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To:     Manivannan Sadhasivam <mani@kernel.org>,
        Krishna chaitanya chundru <quic_krichai@quicinc.com>
CC:     <mhi@lists.linux.dev>, <linux-arm-msm@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <quic_vbadigan@quicinc.com>,
        <quic_ramkri@quicinc.com>, <quic_skananth@quicinc.com>,
        <quic_parass@quicinc.com>
References: <20231023-alignment_check-v1-1-2ca5716d5c15@quicinc.com>
 <20231027130947.GD17527@thinkpad>
From:   Jeffrey Hugo <quic_jhugo@quicinc.com>
In-Reply-To: <20231027130947.GD17527@thinkpad>
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On 10/27/2023 7:09 AM, Manivannan Sadhasivam wrote:
> On Mon, Oct 23, 2023 at 03:13:06PM +0530, Krishna chaitanya chundru wrote:
>> Though we do check the event ring read pointer by "is_valid_ring_ptr"
>> to make sure it is in the buffer range, but there is another risk the
>> pointer may be not aligned.  Since we are expecting event ring elements
>> are 128 bits(struct mhi_tre) aligned, an unaligned read pointer could lead
> 
> "mhi_tre" got renamed to "mhi_ring_element"
> 
>> to multiple issues like DoS or ring buffer memory corruption.
>>
>> So add a alignment check for event ring read pointer.
>>
> 
> Since this is a potential fix, you should add the fixes tag and CC stable.
> 
>> Signed-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
>> ---
>>   drivers/bus/mhi/host/main.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
>> index 499590437e9b..c907bbb67fb2 100644
>> --- a/drivers/bus/mhi/host/main.c
>> +++ b/drivers/bus/mhi/host/main.c
>> @@ -268,7 +268,7 @@ static void mhi_del_ring_element(struct mhi_controller *mhi_cntrl,
>>   
>>   static bool is_valid_ring_ptr(struct mhi_ring *ring, dma_addr_t addr)
>>   {
>> -	return addr >= ring->iommu_base && addr < ring->iommu_base + ring->len;
>> +	return addr >= ring->iommu_base && addr < ring->iommu_base + ring->len && addr % 16 == 0;
> 
> How about,
> 
> !(addr % 16)

We are guaranteed that the ring allocation is 16 byte aligned, right?

I think using "struct mhi_ring_element" instead of "16" would be better.

I'm also thinking that perhaps doing a bit-wise & with a mask would be 
better than the % operator.  Not only is that how these alignment checks 
seem to normally be done elsewhere, but this check is in a critical 
patch for the MHI stack.

-Jeff