[Xen-devel] [PATCH] x86: adjust reserved bit page fault handling

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

One could even debate whether reserved bit faults are always fatal (and
should never be propagated to the guest)...

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

Index: 2008-01-28/xen/arch/x86/traps.c
===================================================================
--- 2008-01-28.orig/xen/arch/x86/traps.c        2008-01-28 11:31:44.000000000 
+0100
+++ 2008-01-28/xen/arch/x86/traps.c     2008-01-30 11:47:39.000000000 +0100
@@ -823,6 +823,17 @@ asmlinkage void do_machine_check(struct 
     machine_check_vector(regs, regs->error_code);
 }
 
+static inline void reserved_bit_page_fault(int guest, unsigned long addr,
+                                           struct cpu_user_regs *regs)
+{
+    if ( guest )
+        gdprintk(XENLOG_ERR, "reserved bit in page table entry: ");
+    else
+        dprintk(XENLOG_ERR, "reserved bit in page table entry: ");
+    show_page_walk(addr);
+    show_execution_state(regs);
+}
+
 void propagate_page_fault(unsigned long addr, u16 error_code)
 {
     struct trap_info *ti;
@@ -852,6 +863,8 @@ void propagate_page_fault(unsigned long 
                v->domain->domain_id, v->vcpu_id, error_code);
         show_page_walk(addr);
     }
+    else if ( unlikely(error_code & PFEC_reserved_bit) )
+        reserved_bit_page_fault(1, addr, guest_cpu_user_regs());
 }
 
 static int handle_gdt_ldt_mapping_fault(
@@ -1034,8 +1047,10 @@ static int fixup_page_fault(unsigned lon
     struct vcpu   *v = current;
     struct domain *d = v->domain;
 
-    /* No fixups in interrupt context or when interrupts are disabled. */
-    if ( in_irq() || !(regs->eflags & X86_EFLAGS_IF) )
+    /* No fixups in interrupt context, when interrupts are disabled, or
+     * when a reserved bit was found to be set. */
+    if ( in_irq() || !(regs->eflags & X86_EFLAGS_IF) ||
+         (regs->error_code & PFEC_reserved_bit) )
         return 0;
 
     if ( unlikely(IN_HYPERVISOR_RANGE(addr)) )
@@ -1101,6 +1116,8 @@ asmlinkage void do_page_fault(struct cpu
         if ( likely((fixup = search_exception_table(regs->eip)) != 0) )
         {
             perfc_incr(copy_user_faults);
+            if ( unlikely(regs->error_code & PFEC_reserved_bit) )
+                reserved_bit_page_fault(0, addr, regs);
             regs->eip = fixup;
             return;
         }




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