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

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

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.


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).


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)
 #ifdef VERBOSE
-    return xsm_default_action(XSM_HOOK, current->domain, NULL);
-    return xsm_default_action(XSM_PRIV, current->domain, NULL);
+    if ( cmd == CONSOLEIO_write )
+        return xsm_default_action(XSM_HOOK, d, NULL);
+    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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