Re: [Qemu-devel] Re: [PATCH RFC] e1000: fix access 4 bytes beyond buffer end

[Michael S. Tsirkin]

On Tue, Jul 13, 2010 at 09:35:49AM +0300, Gleb Natapov wrote:
> On Mon, Jul 12, 2010 at 06:00:20PM -0500, Anthony Liguori wrote:
> > On 07/12/2010 05:42 PM, Michael S. Tsirkin wrote:
> > >On Mon, Jul 12, 2010 at 04:07:21PM -0500, Anthony Liguori wrote:
> > >>On 07/12/2010 12:48 PM, Michael S. Tsirkin wrote:
> > >>>We do range check for size, and get size as buffer,
> > >>>but copy size + 4 bytes (4 is for FCS).
> > >>>Let's copy size bytes but put size + 4 in length.
> > >>>
> > >>>Signed-off-by: Michael S. Tsirkin<address@hidden>
> > >>I think I'd feel slightly better if we zero'd out the FCS before
> > >>writing it to the guest.  It is potentially a data leak.
> > >>
> > >>Regards,
> > >>
> > >>Anthony Liguori
> > >I am guessing there's no chance guest actually looks
> > >at this data, otherwise it won't match and we'd get errors, right?
> > 
> > That's my assumption too.  Although I believe there are some known
> > issues with e1000 and certain versions of Windows and the Microsoft
> > built-in driver.  Maybe this is why those drivers don't work and the
> > Intel drivers do?
> > 
> At least one known issue with Windows drivers to me is that they
> sometimes (on resume from S4 at least) enable interrupts before setup
> irq routing, so if interrupt is generated in the wrong time it hangs the
> guest. I guess it works on real HW for them because line speed
> negotiation takes non-zero time.

I guess we could work around this. Is there a bz?

> > Regards,
> > 
> > Anthony Liguori
> > 
> > >>>---
> > >>>
> > >>>Anthony, Alex, please review.
> > >>>
> > >>>  hw/e1000.c |    3 +--
> > >>>  1 files changed, 1 insertions(+), 2 deletions(-)
> > >>>
> > >>>diff --git a/hw/e1000.c b/hw/e1000.c
> > >>>index 0da65f9..70aba11 100644
> > >>>--- a/hw/e1000.c
> > >>>+++ b/hw/e1000.c
> > >>>@@ -649,7 +649,6 @@ e1000_receive(VLANClientState *nc, const uint8_t 
> > >>>*buf, size_t size)
> > >>>      }
> > >>>
> > >>>      rdh_start = s->mac_reg[RDH];
> > >>>-    size += 4; // for the header
> > >>>      do {
> > >>>          if (s->mac_reg[RDH] == s->mac_reg[RDT]&&   s->check_rxov) {
> > >>>              set_ics(s, 0, E1000_ICS_RXO);
> > >>>@@ -663,7 +662,7 @@ e1000_receive(VLANClientState *nc, const uint8_t 
> > >>>*buf, size_t size)
> > >>>          if (desc.buffer_addr) {
> > >>>              cpu_physical_memory_write(le64_to_cpu(desc.buffer_addr),
> > >>>                                        (void *)(buf + vlan_offset), 
> > >>> size);
> > >>>-            desc.length = cpu_to_le16(size);
> > >>>+            desc.length = cpu_to_le16(size + 4 /* for FCS */);
> > >>>              desc.status |= E1000_RXD_STAT_EOP|E1000_RXD_STAT_IXSM;
> > >>>          } else // as per intel docs; skip descriptors with null buf 
> > >>> addr
> > >>>              DBGOUT(RX, "Null RX descriptor!!\n");
> > 
> 
> --
>                       Gleb.