[Xen-devel] [PATCH] x86/HVM: make explicit that hvm_print_line() does output only

["Jan Beulich" <JBeulich@xxxxxxxx>]

On input "c" being 0xff should already have the effect of bailing early
(due to the isprint()), but let's rather make this explicit. Also
convert the BUG_ON() to an ASSERT() (nothing fatal happens in the
function if this is violated), at the same time extending what is being
checked.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -544,10 +544,14 @@ static int hvm_print_line(
     struct domain *cd = current->domain;
     char c = *val;
 
-    BUG_ON(bytes != 1);
+    ASSERT(bytes == 1 || port == 0xe9);
 
-    /* Accept only printable characters, newline, and horizontal tab. */
-    if ( !isprint(c) && (c != '\n') && (c != '\t') )
+    /*
+     * Ignore any input requests and accept only printable characters,
+     * newline, and horizontal tab.
+     */
+    if ( dir != IOREQ_WRITE ||
+         (!isprint(c) && (c != '\n') && (c != '\t')) )
         return X86EMUL_OKAY;
 
     spin_lock(&cd->pbuf_lock);




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