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

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

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).

------------------------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)

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