linux-kernel - Re: [PATCH] bus: mhi: host: Add alignment check for event ring read pointer

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Message-ID: <3af43db0-0459-733b-ec13-76041eaf8b42@quicinc.com>
Date:   Mon, 30 Oct 2023 12:00:08 +0530
From:   Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To:     Manivannan Sadhasivam <mani@...nel.org>,
        Jeffrey Hugo <quic_jhugo@...cinc.com>
CC:     <mhi@...ts.linux.dev>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_vbadigan@...cinc.com>,
        <quic_ramkri@...cinc.com>, <quic_skananth@...cinc.com>,
        <quic_parass@...cinc.com>
Subject: Re: [PATCH] bus: mhi: host: Add alignment check for event ring read
 pointer


On 10/29/2023 12:56 PM, Manivannan Sadhasivam wrote:
> On Fri, Oct 27, 2023 at 08:19:44AM -0600, Jeffrey Hugo wrote:
>> 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@...cinc.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.
>>
> Yes, both of your suggestions sounds good to me.
>
> Chaitanya, please use below check:
>
> 	!(addr & (sizeof(struct mhi_ring_element) - 1))
>
> - Mani

I will update in the next patch.

- Krishna Chaitanya.

>> -Jeff
>>