From: Thomas Huth <[email protected]> Some machines like the microvm machine instantiate a "sysbus-xhci" device with just 1 interrupt (by setting the "intrs" property to 1). xhci_sysbus_realize() then only allocates the s->irq array with one entry.
When the guest writes to the ERDP register of a corresponding XHCI "interrupter", the generic XHCI code calls the xhci_sysbus_intr_raise() function with n > 1, and this function then calls qemu_set_irq() with s->irq[n] pointing to a bad heap address. The qemu_set_irq() then tries to call an IRQ handler via a function pointer in that heap space. This either causes QEMU to die with a segmentation fault (if it's a bad address), or even worse runs some unexpected code if the destination of the pointer is executable code. Looking at the xHCI spec, it is up to the implementation of the host controller how many interrupters are available. So if we only support one or some few interrupters, the registers of the other interrupters should not do anything, i.e. reads should result in zeros and writes should be completely ignored. (big thanks to Peter Maydell for helping with the analyzation of the correct way to fix this here) This way, the xhci_sysbus_intr_raise() function cannot be called with an invalid interrupt number anymore. But for good measure, also add an assert() statement to the xhci_sysbus_intr_raise() function to prevent that similar problems with calling arbitrary function pointers on the heap could occur again. Fixes: CVE-2026-16043 Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4001 Reported-by: Tristan Madani <[email protected]> Reviewed-by: Peter Maydell <[email protected]> Signed-off-by: Thomas Huth <[email protected]> Message-ID: <[email protected]> (cherry picked from commit cc479aa89743655a725ce29328bcd0585a65983a) Signed-off-by: Michael Tokarev <[email protected]> diff --git a/hw/usb/hcd-xhci-sysbus.c b/hw/usb/hcd-xhci-sysbus.c index ce433223963..9dce3e89cd0 100644 --- a/hw/usb/hcd-xhci-sysbus.c +++ b/hw/usb/hcd-xhci-sysbus.c @@ -20,6 +20,7 @@ static bool xhci_sysbus_intr_raise(XHCIState *xhci, int n, bool level) { XHCISysbusState *s = container_of(xhci, XHCISysbusState, xhci); + assert(n < xhci->numintrs); qemu_set_irq(s->irq[n], level); return false; diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c index 3aeb4f8780f..969f275f32b 100644 --- a/hw/usb/hcd-xhci.c +++ b/hw/usb/hcd-xhci.c @@ -3046,6 +3046,12 @@ static uint64_t xhci_runtime_read(void *ptr, hwaddr reg, } } else { int v = (reg - 0x20) / 0x20; + + if (v >= xhci->numintrs) { + qemu_log_mask(LOG_GUEST_ERROR, + "xhci: read from nonexistent interrupter %i\n", v); + goto out_trace; + } XHCIInterrupter *intr = &xhci->intr[v]; switch (reg & 0x1f) { case 0x00: /* IMAN */ @@ -3072,6 +3078,7 @@ static uint64_t xhci_runtime_read(void *ptr, hwaddr reg, } } +out_trace: trace_usb_xhci_runtime_read(reg, ret); return ret; } @@ -3089,7 +3096,13 @@ static void xhci_runtime_write(void *ptr, hwaddr reg, trace_usb_xhci_unimplemented("runtime write", reg); return; } + v = (reg - 0x20) / 0x20; + if (v >= xhci->numintrs) { + qemu_log_mask(LOG_GUEST_ERROR, + "xhci: write to nonexistent interrupter %i\n", v); + return; + } intr = &xhci->intr[v]; switch (reg & 0x1f) { -- 2.47.3
