From effaf5a240e03020f4ae953e10b764622c3e87cc Mon Sep 17 00:00:00 2001 From: Thomas Huth Date: Thu, 4 Aug 2022 15:13:00 +0200 Subject: [PATCH] hw/usb/hcd-xhci: Fix unbounded loop in xhci_ring_chain_length() (CVE-2020-14394) The loop condition in xhci_ring_chain_length() is under control of the guest, and additionally the code does not check for failed DMA transfers (e.g. if reaching the end of the RAM), so the loop there could run for a very long time or even forever. Fix it by checking the return value of dma_memory_read() and by introducing a maximum loop length. Resolves: https://gitlab.com/qemu-project/qemu/-/issues/646 Message-Id: <20220804131300.96368-1-thuth@redhat.com> Reviewed-by: Mauro Matteo Cascella Acked-by: Gerd Hoffmann Signed-off-by: Thomas Huth --- hw/usb/hcd-xhci.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) --- qemu-5.2+dfsg.orig/hw/usb/hcd-xhci.c +++ qemu-5.2+dfsg/hw/usb/hcd-xhci.c @@ -21,6 +21,7 @@ #include "qemu/osdep.h" #include "qemu/timer.h" +#include "qemu/log.h" #include "qemu/module.h" #include "qemu/queue.h" #include "migration/vmstate.h" @@ -720,9 +721,13 @@ static int xhci_ring_chain_length(XHCISt bool control_td_set = 0; uint32_t link_cnt = 0; - while (1) { + do { TRBType type; - dma_memory_read(xhci->as, dequeue, &trb, TRB_SIZE); + if (dma_memory_read(xhci->as, dequeue, &trb, TRB_SIZE) != MEMTX_OK) { + qemu_log_mask(LOG_GUEST_ERROR, "%s: DMA memory access failed!\n", + __func__); + return -1; + } le64_to_cpus(&trb.parameter); le32_to_cpus(&trb.status); le32_to_cpus(&trb.control); @@ -756,7 +761,17 @@ static int xhci_ring_chain_length(XHCISt if (!control_td_set && !(trb.control & TRB_TR_CH)) { return length; } - } + + /* + * According to the xHCI spec, Transfer Ring segments should have + * a maximum size of 64 kB (see chapter "6 Data Structures") + */ + } while (length < TRB_LINK_LIMIT * 65536 / TRB_SIZE); + + qemu_log_mask(LOG_GUEST_ERROR, "%s: exceeded maximum tranfer ring size!\n", + __func__); + + return -1; } static void xhci_er_reset(XHCIState *xhci, int v)