Re: [PATCH v2] bus: mhi: core: Sanity check values from remote device before use
From: Manivannan Sadhasivam
Date: Wed Feb 24 2021 - 12:43:39 EST
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@xxxxxxxxxxxxxx>
>
> > ---
>
> >
>
> > 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.