From 2543c104ef7f41d32e7f985a826f04d0d98e295d Mon Sep 17 00:00:00 2001 From: Sarah Sharp Date: Thu, 26 Jul 2012 12:03:59 -0700 Subject: [PATCH] xhci: Fix bug after deq ptr set to link TRB. 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. The original upstream commit is 50d0206fcaea3e736f912fd5b00ec6233fb4ce44, but it does not apply to kernels older than 3.4, because inc_deq was changed in 3.3 and 3.4. This patch should apply to the 3.2 kernel and older. Signed-off-by: Sarah Sharp --- drivers/usb/host/xhci-ring.c | 39 ++++++++++++++++++++++-------------- 1 file changed, 24 insertions(+), 15 deletions(-) diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c index fb0981ef8288..c7c530c12439 100644 --- a/drivers/usb/host/xhci-ring.c +++ b/drivers/usb/host/xhci-ring.c @@ -145,25 +145,34 @@ static void next_trb(struct xhci_hcd *xhci, */ static void inc_deq(struct xhci_hcd *xhci, struct xhci_ring *ring, bool consumer) { - union xhci_trb *next = ++(ring->dequeue); unsigned long long addr; ring->deq_updates++; - /* 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 (consumer && last_trb_on_last_seg(xhci, ring, ring->deq_seg, next)) { - ring->cycle_state = (ring->cycle_state ? 0 : 1); - if (!in_interrupt()) - xhci_dbg(xhci, "Toggle cycle state for ring %p = %i\n", - ring, - (unsigned int) ring->cycle_state); + + 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 (consumer && last_trb_on_last_seg(xhci, ring, + ring->deq_seg, ring->dequeue)) { + if (!in_interrupt()) + xhci_dbg(xhci, "Toggle cycle state " + "for ring %p = %i\n", + ring, + (unsigned int) + ring->cycle_state); + 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); } -- 2.39.2