Re: [Qemu-devel] [PATCH] usb/xchi: avoid trigger assertion if guest write wrong epid

[Philippe Mathieu-Daudé]

Hi Mike,

On 4/29/19 9:39 AM, Longpeng(Mike) wrote:
> From: Longpeng <address@hidden>
> 
> we found the following core in our environment:
> 0  0x00007fc6b06c2237 in raise ()
> 1  0x00007fc6b06c3928 in abort ()
> 2  0x00007fc6b06bb056 in __assert_fail_base ()
> 3  0x00007fc6b06bb102 in __assert_fail ()
> 4  0x0000000000702e36 in xhci_kick_ep (...)

  5 xhci_doorbell_write?

> 6  0x000000000047767f in access_with_adjusted_size (...)
> 7  0x000000000047944d in memory_region_dispatch_write (...)
> 8  0x000000000042df17 in address_space_write_continue (...)
> 10 0x000000000043084d in address_space_rw (...)
> 11 0x000000000047451b in kvm_cpu_exec (address@hidden)
> 12 0x000000000045dcf5 in qemu_kvm_cpu_thread_fn (arg=0x1ab11b0)
> 13 0x0000000000870631 in qemu_thread_start (address@hidden)
> 14 0x00000000008959a7 in thread_entry_for_hotfix (pthread_cb=<optimized out>)
> 15 0x00007fc6b0a60dd5 in start_thread ()
> 16 0x00007fc6b078a59d in clone ()
> (gdb) bt
> (gdb) f 5

This is the frame you removed...

> (gdb) p /x tmp
> $9 = 0x62481a00 <-- last byte 0x00 is @epid

I don't see 'tmp' in xhci_doorbell_write().

Can you use trace events?

There we have trace_usb_xhci_doorbell_write().

> 
> xhci_doorbell_write() already check the upper bound of @slotid an @epid,
> it also need to check the lower bound.
> 
> Cc: Gonglei <address@hidden>
> Signed-off-by: Longpeng <address@hidden>
> ---
>  hw/usb/hcd-xhci.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
> index ec28bee..b4e6bfc 100644
> --- a/hw/usb/hcd-xhci.c
> +++ b/hw/usb/hcd-xhci.c
> @@ -3135,9 +3135,9 @@ static void xhci_doorbell_write(void *ptr, hwaddr reg,

Expanding the diff:

       if (reg == 0) {
           if (val == 0) {
               xhci_process_commands(xhci);
           } else {
               DPRINTF("xhci: bad doorbell 0 write: 0x%x\n",
                       (uint32_t)val);
           }
>      } else {
>          epid = val & 0xff;
>          streamid = (val >> 16) & 0xffff;
> -        if (reg > xhci->numslots) {
> +        if (reg == 0 || reg > xhci->numslots) {

So 'reg' can not be zero here...

>              DPRINTF("xhci: bad doorbell %d\n", (int)reg);
> -        } else if (epid > 31) {
> +        } else if (epid == 0 || epid > 31) {

Here neither.

>              DPRINTF("xhci: bad doorbell %d write: 0x%x\n",
>                      (int)reg, (uint32_t)val);
>          } else {
> 

Isn't it the other line that triggered the assertion?

static void xhci_kick_ep(XHCIState *xhci, unsigned int slotid,
                         unsigned int epid, unsigned int streamid)
{
    XHCIEPContext *epctx;

    assert(slotid >= 1 && slotid <= xhci->numslots); // <===
    assert(epid >= 1 && epid <= 31);

Regards,

Phil.