This patch fixes a particularly nasty bug that was revealed by the ring expansion patches. The bug has been present since the very beginning of the xHCI driver history, and could have caused general protection faults from bad memory accesses. The first thing to note is that a Set TR Dequeue Pointer command can move the dequeue pointer to a link TRB, if the canceled or stalled transfer TD ended just before a link TRB. The function to increment the dequeue pointer, inc_deq, was written before cancellation and stall support was added. It assumed that the dequeue pointer could never point to a link TRB. It would unconditionally increment the dequeue pointer at the start of the function, check if the pointer was now on a link TRB, and move it to the top of the next segment if so. This means that if a Set TR Dequeue Point command moved the dequeue pointer to a link TRB, a subsequent call to inc_deq() would move the pointer off the segment and into la-la-land. It would then read from that memory to determine if it was a link TRB. Other functions would often call inc_deq() until the dequeue pointer matched some other pointer, which means this function would quite happily read all of system memory before wrapping around to the right pointer value. Often, there would be another endpoint segment from a different ring allocated from the same DMA pool, which would be contiguous to the segment inc_deq just stepped off of. inc_deq would eventually find the link TRB in that segment, and blindly move the dequeue pointer back to the top of the correct ring segment. The only reason the original code worked at all is because there was only one ring segment. With the ring expansion patches, the dequeue pointer would eventually wrap into place, but the dequeue segment would be out-of-sync. On the second TD after the dequeue pointer was moved to a link TRB, trb_in_td() would fail (because the dequeue pointer and dequeue segment were out-of-sync), and this message would appear: ERROR Transfer event TRB DMA ptr not part of current TD This fixes bugzilla entry 4333 (option-based modem unhappy on USB 3.0 port: "Transfer event TRB DMA ptr not part of current TD", "rejecting I/O to offline device"), https://bugzilla.kernel.org/show_bug.cgi?id=43333 and possibly other general protection fault bugs as well. This patch should be backported to kernels as old as 2.6.31. A separate patch will be created for kernels older than 3.4, since inc_deq was modified in 3.4 and this patch will not apply. Signed-off-by: Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx> Tested-by: James Ettle <theholyettlz@xxxxxxxxxxxxxx> Tested-by: Matthew Hall <mhall@xxxxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx --- drivers/usb/host/xhci-ring.c | 36 ++++++++++++++++++++++-------------- 1 files changed, 22 insertions(+), 14 deletions(-) diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c index 0c93f5d..643c2f3 100644 --- a/drivers/usb/host/xhci-ring.c +++ b/drivers/usb/host/xhci-ring.c @@ -145,29 +145,37 @@ static void next_trb(struct xhci_hcd *xhci, */ static void inc_deq(struct xhci_hcd *xhci, struct xhci_ring *ring) { - union xhci_trb *next; unsigned long long addr; ring->deq_updates++; - /* If this is not event ring, there is one more usable TRB */ + /* + * If this is not event ring, and the dequeue pointer + * is not on a link TRB, there is one more usable TRB + */ if (ring->type != TYPE_EVENT && !last_trb(xhci, ring, ring->deq_seg, ring->dequeue)) ring->num_trbs_free++; - next = ++(ring->dequeue); - /* Update the dequeue pointer further if that was a link TRB or we're at - * the end of an event ring segment (which doesn't have link TRBS) - */ - while (last_trb(xhci, ring, ring->deq_seg, next)) { - if (ring->type == TYPE_EVENT && last_trb_on_last_seg(xhci, - ring, ring->deq_seg, next)) { - ring->cycle_state = (ring->cycle_state ? 0 : 1); + do { + /* + * Update the dequeue pointer further if that was a link TRB or + * we're at the end of an event ring segment (which doesn't have + * link TRBS) + */ + if (last_trb(xhci, ring, ring->deq_seg, ring->dequeue)) { + if (ring->type == TYPE_EVENT && + last_trb_on_last_seg(xhci, ring, + ring->deq_seg, ring->dequeue)) { + ring->cycle_state = (ring->cycle_state ? 0 : 1); + } + ring->deq_seg = ring->deq_seg->next; + ring->dequeue = ring->deq_seg->trbs; + } else { + ring->dequeue++; } - ring->deq_seg = ring->deq_seg->next; - ring->dequeue = ring->deq_seg->trbs; - next = ring->dequeue; - } + } while (last_trb(xhci, ring, ring->deq_seg, ring->dequeue)); + addr = (unsigned long long) xhci_trb_virt_to_dma(ring->deq_seg, ring->dequeue); } -- 1.7.9 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
