[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH 1/2] xen/xsm: forbid PV guest console reads



On 09/30/2013 02:06 PM, Konrad Rzeszutek Wilk wrote:
On Mon, Sep 30, 2013 at 01:29:00PM -0400, Daniel De Graaf wrote:
On 09/30/2013 12:10 PM, Jan Beulich wrote:
On 30.09.13 at 17:48, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
When the hypervisor was compiled in debug mode (with VERBOSE defined),
PV guests incorrectly had access to both read and write to the console.
Change this to only allow write access; since such writes were limited
by log levels in 48d50de8e0, remove the dependency on VERBOSE
completely.

I disagree, and iirc I disagreed already when you tried to drop the
dependency on VERBOSE with that earlier patch.

Reported-by: Jan Beulich <JBeulich@xxxxxxxx>
Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
---

Alternatively, if controlling writes with VERBOSE is still desired, the
ifdef VERBOSE can be retained surrounding the if() with the following
commit message:



That's what I'd want to see go in.

Jan

This patch retains the existing behavior where only HVM guests can use
the console for output, and only via the 0xE9 I/O port. With Konrad's
Linux patch, this means that xen_raw_console_write in non-dom0 will
produce output only on Xen <= 4.3 (which returns -ENOSYS rather than
-EPERM, as this code does).

I was under the impression that what we wanted is:
   - normal PV guests can do console_write
   - HVM guests can do console_write
   - priv guests (irregardless if they are HVM or PV) can do console_write
     _and_ console_read.

Which I think the patch below still allows right?

All of your bullets are true if the hypervisor is compiled with VERBOSE
(which is enabled if debug=y). Otherwise, only priv guests will be able
to use console_write (and it won't matter if they are PV or HVM). Either
way, only priv guests will be able to use console_read - which is the
only thing the below patch actually changes.


------------------------8<----------------------------------------------

The CONSOLEIO_read operation was incorrectly allowed to PV guests if the
hypervisor was compiled in debug mode (with VERBOSE defined).

Reported-by: Jan Beulich <JBeulich@xxxxxxxx>
Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
---
  xen/include/xsm/dummy.h | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index 2abf018..b1edd29 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -233,10 +233,10 @@ static XSM_INLINE int xsm_console_io(XSM_DEFAULT_ARG 
struct domain *d, int cmd)
  {
      XSM_ASSERT_ACTION(XSM_OTHER);
  #ifdef VERBOSE
-    return xsm_default_action(XSM_HOOK, current->domain, NULL);
-#else
-    return xsm_default_action(XSM_PRIV, current->domain, NULL);
+    if ( cmd == CONSOLEIO_write )
+        return xsm_default_action(XSM_HOOK, d, NULL);
  #endif
+    return xsm_default_action(XSM_PRIV, d, NULL);
  }
  static XSM_INLINE int xsm_profile(XSM_DEFAULT_ARG struct domain *d, int op)





--
Daniel De Graaf
National Security Agency

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.