From d8c2e6f2f6d29ccb766197181eb1c65c1d46b3a4 Mon Sep 17 00:00:00 2001 From: Qiang Liu Date: Fri, 26 Aug 2022 13:15:56 +0800 Subject: [PATCH] hcd-ohci: Drop ohci_service_iso_td() if ed->head & OHCI_DPTR_MASK is zero An abort happens in ohci_frame_boundary() when ohci->done is 0 [1]. ``` c static void ohci_frame_boundary(void *opaque) { // ... if (ohci->done_count == 0 && !(ohci->intr_status & OHCI_INTR_WD)) { if (!ohci->done) abort(); <----------------------------------------- [1] ``` This was reported in https://bugs.launchpad.net/qemu/+bug/1911216/, https://lists.gnu.org/archive/html/qemu-devel/2021-06/msg03613.html, and https://gitlab.com/qemu-project/qemu/-/issues/545. I can still reproduce it with the latest QEMU. This happends due to crafted ED with putting ISO_TD at physical address 0. Suppose ed->head & OHCI_DPTR_MASK is 0 [2], and we memset 0 to the phyiscal memory from 0 to sizeof(ohci_iso_td). Then, starting_frame [3] and frame_count [4] are both 0. As we can control the value of ohci->frame_number (0 to 0x1f, suppose 1), we then control the value of relative_frame_number to be 1 [6]. The control flow goes to [7] where ohci->done is 0. Have returned from ohci_service_iso_td(), ohci_frame_boundary() will abort() [1]. ``` c static int ohci_service_iso_td(OHCIState *ohci, struct ohci_ed *ed) { // ... addr = ed->head & OHCI_DPTR_MASK; // <--------------------- [2] if (ohci_read_iso_td(ohci, addr, &iso_td)) { // <-------- [3] // ... starting_frame = OHCI_BM(iso_td.flags, TD_SF); // <-------- [4] frame_count = OHCI_BM(iso_td.flags, TD_FC); // <-------- [5] relative_frame_number = USUB(ohci->frame_number, starting_frame); // <-------- [6] if (relative_frame_number < 0) { return 1; } else if (relative_frame_number > frame_count) { // ... ohci->done = addr; // <-------- [7] // ... } ``` As only (afaik) a guest root user can manipulate ED, TD and the physical memory, this assertion failure is not a security bug. The idea to fix this issue is to drop ohci_service_iso_td() if ed->head & OHCI_DPTR_MASK is 0, which is similar to the drop operation for ohci_service_ed_list() when head is 0. Probably, a similar issue is in ohci_service_td(). I drop ohci_service_td() if ed->head & OHCI_DPTR_MASK is 0. Fixes: 7bfe577702 ("OHCI USB isochronous transfers support (Arnon Gilboa)") Reported-by: Gaoning Pan Reported-by: Alexander Bulekov Reported-by: Qiang Liu Resolves: https://gitlab.com/qemu-project/qemu/-/issues/545 Buglink: https://lists.gnu.org/archive/html/qemu-devel/2021-06/msg03613.html Buglink: https://bugs.launchpad.net/qemu/+bug/1911216 Signed-off-by: Qiang Liu Message-Id: <20220826051557.119570-1-cyruscyliu@gmail.com> Signed-off-by: Gerd Hoffmann --- hw/usb/hcd-ohci.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/hw/usb/hcd-ohci.c b/hw/usb/hcd-ohci.c index 895b29fb86..72bdde9261 100644 --- a/hw/usb/hcd-ohci.c +++ b/hw/usb/hcd-ohci.c @@ -571,6 +571,11 @@ static int ohci_service_iso_td(OHCIState *ohci, struct ohci_ed *ed) addr = ed->head & OHCI_DPTR_MASK; + if (addr == 0) { + ohci_die(ohci); + return 1; + } + if (ohci_read_iso_td(ohci, addr, &iso_td)) { trace_usb_ohci_iso_td_read_failed(addr); ohci_die(ohci); @@ -858,6 +863,11 @@ static int ohci_service_td(OHCIState *ohci, struct ohci_ed *ed) int completion; addr = ed->head & OHCI_DPTR_MASK; + if (addr == 0) { + ohci_die(ohci); + return 1; + } + /* See if this TD has already been submitted to the device. */ completion = (addr == ohci->async_td); if (completion && !ohci->async_complete) { -- 2.11.0