[Xen-devel] [PATCH v3 4/5] x86/HVM: refuse CR3 loads with reserved (upper) bits set

[Jan Beulich <jbeulich@xxxxxxxx>]

While bits 11 and below are, if not used for other purposes, reserved
but ignored, bits beyond physical address width are supposed to raise
exceptions (at least in the non-nested case; I'm not convinced the
current nested SVM/VMX behavior of raising #GP(0) here is correct, but
that's not the subject of this change).

Introduce currd as a local variable, and replace other v->domain
instances at the same time.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
v3: Correct return value in hvm_load_cpu_ctxt(). Re-base.
v2: Simplify the expressions used for the reserved bit checks.

---
 xen/arch/x86/hvm/hvm.c |   24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1016,6 +1016,13 @@ static int hvm_load_cpu_ctxt(struct doma
         return -EINVAL;
     }
 
+    if ( ctxt.cr3 >> d->arch.cpuid->extd.maxphysaddr )
+    {
+        printk(XENLOG_G_ERR "HVM%d restore: bad CR3 %#" PRIx64 "\n",
+               d->domain_id, ctxt.cr3);
+        return -EINVAL;
+    }
+
     if ( (ctxt.flags & ~XEN_X86_FPU_INITIALISED) != 0 )
     {
         gprintk(XENLOG_ERR, "bad flags value in CPU context: %#x\n",
@@ -2303,10 +2310,18 @@ int hvm_set_cr0(unsigned long value, boo
 int hvm_set_cr3(unsigned long value, bool noflush, bool may_defer)
 {
     struct vcpu *v = current;
+    struct domain *currd = v->domain;
     struct page_info *page;
     unsigned long old = v->arch.hvm.guest_cr[3];
 
-    if ( may_defer && unlikely(v->domain->arch.monitor.write_ctrlreg_enabled &
+    if ( value >> currd->arch.cpuid->extd.maxphysaddr )
+    {
+        HVM_DBG_LOG(DBG_LEVEL_1,
+                    "Attempt to set reserved CR3 bit(s): %lx", value);
+        return X86EMUL_EXCEPTION;
+    }
+
+    if ( may_defer && unlikely(currd->arch.monitor.write_ctrlreg_enabled &
                                monitor_ctrlreg_bitmask(VM_EVENT_X86_CR3)) )
     {
         ASSERT(v->arch.vm_event);
@@ -2322,13 +2337,12 @@ int hvm_set_cr3(unsigned long value, boo
         }
     }
 
-    if ( hvm_paging_enabled(v) && !paging_mode_hap(v->domain) &&
+    if ( hvm_paging_enabled(v) && !paging_mode_hap(currd) &&
          ((value ^ v->arch.hvm.guest_cr[3]) >> PAGE_SHIFT) )
     {
         /* Shadow-mode CR3 change. Check PDBR and update refcounts. */
         HVM_DBG_LOG(DBG_LEVEL_VMMU, "CR3 value = %lx", value);
-        page = get_page_from_gfn(v->domain, value >> PAGE_SHIFT,
-                                 NULL, P2M_ALLOC);
+        page = get_page_from_gfn(currd, value >> PAGE_SHIFT, NULL, P2M_ALLOC);
         if ( !page )
             goto bad_cr3;
 
@@ -2344,7 +2358,7 @@ int hvm_set_cr3(unsigned long value, boo
 
  bad_cr3:
     gdprintk(XENLOG_ERR, "Invalid CR3\n");
-    domain_crash(v->domain);
+    domain_crash(currd);
     return X86EMUL_UNHANDLEABLE;
 }
 


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