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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Wed, Feb 24, 2021 at 08:10:06AM -0700, Jeffrey Hugo wrote:
> 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@codeaurora.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.
> 

Okay. Please mention it in the commit message. Currently it mentions
only the tre pointer.

Thanks,
Mani

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