[PATCH] hw/usb/hcd-dwc2: Enforce epnum to 0 for the control endpoint to avoid the assertion failure in usb_ep_get()

[PATCH] hw/usb/hcd-dwc2: Enforce epnum to 0 for the control endpoint to avoid the assertion failure in usb_ep_get()

[Qiang Liu]

When eptype is USB_ENDPOINT_XFER_CONTROL and pid is
TSIZ_SC_MC_PID_SETUP, usb_ep_get() should return the control endpoint.
In hw/usb/core.c, the assumed epnum of the control endpoint is 0. When
epnum is not 0, usb_ep_get() will crash due to the check assert(pid ==
USB_TOKEN_IN || pid == USB_TOKEN_OUT).

The description
http://www.capital-micro.com/PDF/CME-M7_Family_User_Guide_EN.pdf
(18.5.3.4 (14), 18.5.3.4 (10)) a) mentions that the pid is maintained by
the host, b) but doesn't mention that whether the epnum should be 0 for
the control endpoint. However, usb_ep_get() assumes it is 0. To avoid
potential assertion failure in usb_ep_get(), we could enforce epnum to 0
and warn users.

Fixes: 153ef1662c3 ("dwc-hsotg (dwc2) USB host controller emulation")
Signed-off-by: Qiang Liu <cyruscyliu@gmail.com>
---
 hw/usb/hcd-dwc2.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/usb/hcd-dwc2.c b/hw/usb/hcd-dwc2.c
index e1d96ac..65d9d46 100644
--- a/hw/usb/hcd-dwc2.c
+++ b/hw/usb/hcd-dwc2.c
@@ -636,6 +636,11 @@ static void dwc2_enable_chan(DWC2State *s,  uint32_t index)
     }
 
     if (eptype == USB_ENDPOINT_XFER_CONTROL && pid == TSIZ_SC_MC_PID_SETUP) {
+        if (epnum != 0) {
+            qemu_log_mask(LOG_GUEST_ERROR,
+                          "epnum should be 0 for the control endpoint\n");
+            epnum = 0;
+        }
         pid = USB_TOKEN_SETUP;
     } else {
         pid = epdir ? USB_TOKEN_IN : USB_TOKEN_OUT;
-- 
2.7.4

Re: [PATCH] hw/usb/hcd-dwc2: Enforce epnum to 0 for the control endpoint to avoid the assertion failure in usb_ep_get()

[Qiang Liu]

Hi folks,

I found this bug by my dwc2 fuzzer.
It seems that
* https://bugs.launchpad.net/qemu/+bug/1907042
* https://bugs.launchpad.net/qemu/+bug/1525123
or
* https://gitlab.com/qemu-project/qemu/-/issues/119
* https://gitlab.com/qemu-project/qemu/-/issues/303
have reported similar issues.

Would it be better to consider and fix them together?

Best,
Qiang

On Sun, Jun 27, 2021 at 11:28 AM Qiang Liu <cyruscyliu@gmail.com> wrote:
>
> When eptype is USB_ENDPOINT_XFER_CONTROL and pid is
> TSIZ_SC_MC_PID_SETUP, usb_ep_get() should return the control endpoint.
> In hw/usb/core.c, the assumed epnum of the control endpoint is 0. When
> epnum is not 0, usb_ep_get() will crash due to the check assert(pid ==
> USB_TOKEN_IN || pid == USB_TOKEN_OUT).
>
> The description
> http://www.capital-micro.com/PDF/CME-M7_Family_User_Guide_EN.pdf
> (18.5.3.4 (14), 18.5.3.4 (10)) a) mentions that the pid is maintained by
> the host, b) but doesn't mention that whether the epnum should be 0 for
> the control endpoint. However, usb_ep_get() assumes it is 0. To avoid
> potential assertion failure in usb_ep_get(), we could enforce epnum to 0
> and warn users.
>
> Fixes: 153ef1662c3 ("dwc-hsotg (dwc2) USB host controller emulation")
> Signed-off-by: Qiang Liu <cyruscyliu@gmail.com>
> ---
>  hw/usb/hcd-dwc2.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/hw/usb/hcd-dwc2.c b/hw/usb/hcd-dwc2.c
> index e1d96ac..65d9d46 100644
> --- a/hw/usb/hcd-dwc2.c
> +++ b/hw/usb/hcd-dwc2.c
> @@ -636,6 +636,11 @@ static void dwc2_enable_chan(DWC2State *s,  uint32_t index)
>      }
>
>      if (eptype == USB_ENDPOINT_XFER_CONTROL && pid == TSIZ_SC_MC_PID_SETUP) {
> +        if (epnum != 0) {
> +            qemu_log_mask(LOG_GUEST_ERROR,
> +                          "epnum should be 0 for the control endpoint\n");
> +            epnum = 0;
> +        }
>          pid = USB_TOKEN_SETUP;
>      } else {
>          pid = epdir ? USB_TOKEN_IN : USB_TOKEN_OUT;
> --
> 2.7.4
>

Re: [PATCH] hw/usb/hcd-dwc2: Enforce epnum to 0 for the control endpoint to avoid the assertion failure in usb_ep_get()

[Paul Zimmerman]

On Sat, Jun 26, 2021 at 10:21 PM Qiang Liu <cyruscyliu@gmail.com> wrote:
>
> Hi folks,
>
> I found this bug by my dwc2 fuzzer.
> It seems that
> * https://bugs.launchpad.net/qemu/+bug/1907042
> * https://bugs.launchpad.net/qemu/+bug/1525123
> or
> * https://gitlab.com/qemu-project/qemu/-/issues/119
> * https://gitlab.com/qemu-project/qemu/-/issues/303
> have reported similar issues.
>
> Would it be better to consider and fix them together?
>
> Best,
> Qiang
>
> On Sun, Jun 27, 2021 at 11:28 AM Qiang Liu <cyruscyliu@gmail.com> wrote:
> >
> > When eptype is USB_ENDPOINT_XFER_CONTROL and pid is
> > TSIZ_SC_MC_PID_SETUP, usb_ep_get() should return the control endpoint.
> > In hw/usb/core.c, the assumed epnum of the control endpoint is 0. When
> > epnum is not 0, usb_ep_get() will crash due to the check assert(pid ==
> > USB_TOKEN_IN || pid == USB_TOKEN_OUT).
> >
> > The description
> > http://www.capital-micro.com/PDF/CME-M7_Family_User_Guide_EN.pdf
> > (18.5.3.4 (14), 18.5.3.4 (10)) a) mentions that the pid is maintained by
> > the host, b) but doesn't mention that whether the epnum should be 0 for
> > the control endpoint. However, usb_ep_get() assumes it is 0. To avoid
> > potential assertion failure in usb_ep_get(), we could enforce epnum to 0
> > and warn users.
> >
> > Fixes: 153ef1662c3 ("dwc-hsotg (dwc2) USB host controller emulation")
> > Signed-off-by: Qiang Liu <cyruscyliu@gmail.com>
> > ---
> >  hw/usb/hcd-dwc2.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/hw/usb/hcd-dwc2.c b/hw/usb/hcd-dwc2.c
> > index e1d96ac..65d9d46 100644
> > --- a/hw/usb/hcd-dwc2.c
> > +++ b/hw/usb/hcd-dwc2.c
> > @@ -636,6 +636,11 @@ static void dwc2_enable_chan(DWC2State *s,  uint32_t index)
> >      }
> >
> >      if (eptype == USB_ENDPOINT_XFER_CONTROL && pid == TSIZ_SC_MC_PID_SETUP) {
> > +        if (epnum != 0) {
> > +            qemu_log_mask(LOG_GUEST_ERROR,
> > +                          "epnum should be 0 for the control endpoint\n");
> > +            epnum = 0;
> > +        }
> >          pid = USB_TOKEN_SETUP;
> >      } else {
> >          pid = epdir ? USB_TOKEN_IN : USB_TOKEN_OUT;
> > --
> > 2.7.4
> >

Hi Qiang,

Sorry for the late reply, I've had a busy week.
Yes, I think it would be best to fix this in the core since it affects more
than one host. I'm not sure that forcing the Control endpoint to 0 is
the best solution though, perhaps it would be better to print an error
message and fail the operation? AFAIK there are no real-world devices
that have Control endpoints other than 0, although I believe it is allowed
by the USB spec.

Let's wait and see what Gerd thinks.

- Paul

Re: [PATCH] hw/usb/hcd-dwc2: Enforce epnum to 0 for the control endpoint to avoid the assertion failure in usb_ep_get()

[Qiang Liu]

Hi Paul,

On Mon, Jul 5, 2021 at 6:27 AM Paul Zimmerman <pauldzim@gmail.com> wrote:
>
> On Sat, Jun 26, 2021 at 10:21 PM Qiang Liu <cyruscyliu@gmail.com> wrote:
> >
> > Hi folks,
> >
> > I found this bug by my dwc2 fuzzer.
> > It seems that
> > * https://bugs.launchpad.net/qemu/+bug/1907042
> > * https://bugs.launchpad.net/qemu/+bug/1525123
> > or
> > * https://gitlab.com/qemu-project/qemu/-/issues/119
> > * https://gitlab.com/qemu-project/qemu/-/issues/303
> > have reported similar issues.
> >
> > Would it be better to consider and fix them together?
> >
> > Best,
> > Qiang
> >
> > On Sun, Jun 27, 2021 at 11:28 AM Qiang Liu <cyruscyliu@gmail.com> wrote:
> > >
> > > When eptype is USB_ENDPOINT_XFER_CONTROL and pid is
> > > TSIZ_SC_MC_PID_SETUP, usb_ep_get() should return the control endpoint.
> > > In hw/usb/core.c, the assumed epnum of the control endpoint is 0. When
> > > epnum is not 0, usb_ep_get() will crash due to the check assert(pid ==
> > > USB_TOKEN_IN || pid == USB_TOKEN_OUT).
> > >
> > > The description
> > > http://www.capital-micro.com/PDF/CME-M7_Family_User_Guide_EN.pdf
> > > (18.5.3.4 (14), 18.5.3.4 (10)) a) mentions that the pid is maintained by
> > > the host, b) but doesn't mention that whether the epnum should be 0 for
> > > the control endpoint. However, usb_ep_get() assumes it is 0. To avoid
> > > potential assertion failure in usb_ep_get(), we could enforce epnum to 0
> > > and warn users.
> > >
> > > Fixes: 153ef1662c3 ("dwc-hsotg (dwc2) USB host controller emulation")
> > > Signed-off-by: Qiang Liu <cyruscyliu@gmail.com>
> > > ---
> > >  hw/usb/hcd-dwc2.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/hw/usb/hcd-dwc2.c b/hw/usb/hcd-dwc2.c
> > > index e1d96ac..65d9d46 100644
> > > --- a/hw/usb/hcd-dwc2.c
> > > +++ b/hw/usb/hcd-dwc2.c
> > > @@ -636,6 +636,11 @@ static void dwc2_enable_chan(DWC2State *s,  uint32_t index)
> > >      }
> > >
> > >      if (eptype == USB_ENDPOINT_XFER_CONTROL && pid == TSIZ_SC_MC_PID_SETUP) {
> > > +        if (epnum != 0) {
> > > +            qemu_log_mask(LOG_GUEST_ERROR,
> > > +                          "epnum should be 0 for the control endpoint\n");
> > > +            epnum = 0;
> > > +        }
> > >          pid = USB_TOKEN_SETUP;
> > >      } else {
> > >          pid = epdir ? USB_TOKEN_IN : USB_TOKEN_OUT;
> > > --
> > > 2.7.4
> > >
>
> Hi Qiang,
>
> Sorry for the late reply, I've had a busy week.
> Yes, I think it would be best to fix this in the core since it affects more
> than one host.
My current fix is in the following.

diff --git a/hw/usb/core.c b/hw/usb/core.c
index 975f762..a29b378 100644
--- a/hw/usb/core.c
+++ b/hw/usb/core.c
@@ -735,10 +735,11 @@ void usb_ep_dump(USBDevice *dev)

 struct USBEndpoint *usb_ep_get(USBDevice *dev, int pid, int ep)
 {
     struct USBEndpoint *eps;

     assert(dev != NULL);
-    if (ep == 0) {
+    if (ep == 0 || pid == USB_TOKEN_SETUP) {
         return &dev->ep_ctl;
     }
     assert(pid == USB_TOKEN_IN || pid == USB_TOKEN_OUT);

>I'm not sure that forcing the Control endpoint to 0 is
> the best solution though, perhaps it would be better to print an error
> message and fail the operation? AFAIK there are no real-world devices
> that have Control endpoints other than 0, although I believe it is allowed
> by the USB spec.
I think, as a malicious guest, if the spec allows, it can set the
control endpoint to non-zero.

> Let's wait and see what Gerd thinks.
Yes!

Best,
Qiang

Re: [PATCH] hw/usb/hcd-dwc2: Enforce epnum to 0 for the control endpoint to avoid the assertion failure in usb_ep_get()

[Gerd Hoffmann]

> > > * https://gitlab.com/qemu-project/qemu/-/issues/119
> > > * https://gitlab.com/qemu-project/qemu/-/issues/303

> diff --git a/hw/usb/core.c b/hw/usb/core.c
> index 975f762..a29b378 100644
> --- a/hw/usb/core.c
> +++ b/hw/usb/core.c
> @@ -735,10 +735,11 @@ void usb_ep_dump(USBDevice *dev)
> 
>  struct USBEndpoint *usb_ep_get(USBDevice *dev, int pid, int ep)
>  {
>      struct USBEndpoint *eps;
> 
>      assert(dev != NULL);
> -    if (ep == 0) {
> +    if (ep == 0 || pid == USB_TOKEN_SETUP) {
>          return &dev->ep_ctl;
>      }

Looks sane to me, although I'm not sure it matches what
real hardware does.

Can you submit that as proper patch (including Resolves: for the gitlab
issues fixed)?

> > message and fail the operation? AFAIK there are no real-world devices
> > that have Control endpoints other than 0, although I believe it is allowed
> > by the USB spec.

IIRC control endpoint is zero by spec.

thanks & take care,
  Gerd