linux-kernel - Re: [PATCH v2] bus: mhi: core: Sanity check values from remote device before use

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Date:   Wed, 24 Feb 2021 08:10:06 -0700
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     hemantk@...eaurora.org, bbhatt@...eaurora.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] bus: mhi: core: Sanity check values from remote device
 before use

On 2/24/2021 2:47 AM, Manivannan Sadhasivam wrote:
> On Wed, Feb 17, 2021 at 09:20:22AM -0700, Jeffrey Hugo wrote:
>> When parsing the structures in the shared memory, there are values which
>> come from the remote device.  For example, a transfer completion event
>> will have a pointer to the tre in the relevant channel's transfer ring.
>> Such values should be considered to be untrusted, and validated before
>> use.  If we blindly use such values, we may access invalid data or crash
>> if the values are corrupted.
>>
>> If validation fails, drop the relevant event.
>>
>> Signed-off-by: Jeffrey Hugo <jhugo@...eaurora.org>
>> ---
>>
>> v2: Fix subject
>>
>>   drivers/bus/mhi/core/main.c | 81 +++++++++++++++++++++++++++++++++++++++++----
>>   1 file changed, 74 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
>> index c043574..1eb2fd3 100644
>> --- a/drivers/bus/mhi/core/main.c
>> +++ b/drivers/bus/mhi/core/main.c
>> @@ -242,6 +242,11 @@ static void mhi_del_ring_element(struct mhi_controller *mhi_cntrl,
>>   	smp_wmb();
>>   }
>>   
>> +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;
>> +}
>> +
>>   int mhi_destroy_device(struct device *dev, void *data)
>>   {
>>   	struct mhi_device *mhi_dev;
>> @@ -383,7 +388,16 @@ irqreturn_t mhi_irq_handler(int irq_number, void *dev)
>>   	struct mhi_event_ctxt *er_ctxt =
>>   		&mhi_cntrl->mhi_ctxt->er_ctxt[mhi_event->er_index];
>>   	struct mhi_ring *ev_ring = &mhi_event->ring;
>> -	void *dev_rp = mhi_to_virtual(ev_ring, er_ctxt->rp);
>> +	dma_addr_t ptr = er_ctxt->rp;
>> +	void *dev_rp;
>> +
>> +	if (!is_valid_ring_ptr(ev_ring, ptr)) {
>> +		dev_err(&mhi_cntrl->mhi_dev->dev,
>> +			"Event ring rp points outside of the event ring\n");
>> +		return IRQ_HANDLED;
>> +	}
>> +
>> +	dev_rp = mhi_to_virtual(ev_ring, ptr);
>>   
>>   	/* Only proceed if event ring has pending events */
>>   	if (ev_ring->rp == dev_rp)
>> @@ -536,6 +550,11 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
>>   		struct mhi_buf_info *buf_info;
>>   		u16 xfer_len;
>>   
>> +		if (!is_valid_ring_ptr(tre_ring, ptr)) {
>> +			dev_err(&mhi_cntrl->mhi_dev->dev,
>> +				"Event element points outside of the tre ring\n");
>> +			break;
>> +		}
>>   		/* Get the TRB this event points to */
>>   		ev_tre = mhi_to_virtual(tre_ring, ptr);
>>   
>> @@ -695,6 +714,12 @@ static void mhi_process_cmd_completion(struct mhi_controller *mhi_cntrl,
>>   	struct mhi_chan *mhi_chan;
>>   	u32 chan;
>>   
>> +	if (!is_valid_ring_ptr(mhi_ring, ptr)) {
>> +		dev_err(&mhi_cntrl->mhi_dev->dev,
>> +			"Event element points outside of the cmd ring\n");
>> +		return;
>> +	}
>> +
>>   	cmd_pkt = mhi_to_virtual(mhi_ring, ptr);
>>   
>>   	chan = MHI_TRE_GET_CMD_CHID(cmd_pkt);
>> @@ -719,6 +744,7 @@ int mhi_process_ctrl_ev_ring(struct mhi_controller *mhi_cntrl,
>>   	struct device *dev = &mhi_cntrl->mhi_dev->dev;
>>   	u32 chan;
>>   	int count = 0;
>> +	dma_addr_t ptr = er_ctxt->rp;
>>   
>>   	/*
>>   	 * This is a quick check to avoid unnecessary event processing
>> @@ -728,7 +754,13 @@ int mhi_process_ctrl_ev_ring(struct mhi_controller *mhi_cntrl,
>>   	if (unlikely(MHI_EVENT_ACCESS_INVALID(mhi_cntrl->pm_state)))
>>   		return -EIO;
>>   
>> -	dev_rp = mhi_to_virtual(ev_ring, er_ctxt->rp);
>> +	if (!is_valid_ring_ptr(ev_ring, ptr)) {
>> +		dev_err(&mhi_cntrl->mhi_dev->dev,
>> +			"Event ring rp points outside of the event ring\n");
>> +		return -EIO;
>> +	}
>> +
>> +	dev_rp = mhi_to_virtual(ev_ring, ptr);
>>   	local_rp = ev_ring->rp;
>>   
>>   	while (dev_rp != local_rp) {
>> @@ -834,6 +866,8 @@ int mhi_process_ctrl_ev_ring(struct mhi_controller *mhi_cntrl,
>>   			 */
>>   			if (chan < mhi_cntrl->max_chan) {
>>   				mhi_chan = &mhi_cntrl->mhi_chan[chan];
>> +				if (!mhi_chan->configured)
>> +					break;
> 
> This change is not part of this patch I believe.

It is.  The remote device specified an event on a channel.  We already 
check to see that the specified channel value doesn't exceed the maximum 
number of channels, but we don't check to see that it is a valid channel 
within the range of channels.  If its not a valid channel (say 0-5 and 
7-10 are valid, max is 10, but the remote end specified 6), bad things 
could happen because we are implicitly trusting the value before fully 
checking its validity.

This is still a sanity check of a value from the remote end.

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