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

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

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