x86: properly handle hvm_copy_from_guest_{phys,virt}() errors

Ignoring them generally implies using uninitialized data and, in all
cases dealt with here, potentially leaking hypervisor stack contents to
guests.

This is XSA-63.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2308,11 +2308,7 @@ void hvm_task_switch(
 
     rc = hvm_copy_from_guest_virt(
         &tss, prev_tr.base, sizeof(tss), PFEC_page_present);
-    if ( rc == HVMCOPY_bad_gva_to_gfn )
-        goto out;
-    if ( rc == HVMCOPY_gfn_paged_out )
-        goto out;
-    if ( rc == HVMCOPY_gfn_shared )
+    if ( rc != HVMCOPY_okay )
         goto out;
 
     eflags = regs->eflags;
@@ -2357,13 +2353,11 @@ void hvm_task_switch(
 
     rc = hvm_copy_from_guest_virt(
         &tss, tr.base, sizeof(tss), PFEC_page_present);
-    if ( rc == HVMCOPY_bad_gva_to_gfn )
-        goto out;
-    if ( rc == HVMCOPY_gfn_paged_out )
-        goto out;
-    /* Note: this could be optimised, if the callee functions knew we want RO
-     * access */
-    if ( rc == HVMCOPY_gfn_shared )
+    /*
+     * Note: The HVMCOPY_gfn_shared case could be optimised, if the callee
+     * functions knew we want RO access.
+     */
+    if ( rc != HVMCOPY_okay )
         goto out;
 
 
--- a/xen/arch/x86/hvm/intercept.c
+++ b/xen/arch/x86/hvm/intercept.c
@@ -87,17 +87,28 @@ static int hvm_mmio_access(struct vcpu *
     {
         for ( i = 0; i < p->count; i++ )
         {
-            int ret;
-
-            ret = hvm_copy_from_guest_phys(&data,
-                                           p->data + (sign * i * p->size),
-                                           p->size);
-            if ( (ret == HVMCOPY_gfn_paged_out) || 
-                 (ret == HVMCOPY_gfn_shared) )
+            switch ( hvm_copy_from_guest_phys(&data,
+                                              p->data + sign * i * p->size,
+                                              p->size) )
             {
+            case HVMCOPY_okay:
+                break;
+            case HVMCOPY_gfn_paged_out:
+            case HVMCOPY_gfn_shared:
                 rc = X86EMUL_RETRY;
                 break;
+            case HVMCOPY_bad_gfn_to_mfn:
+                data = ~0;
+                break;
+            case HVMCOPY_bad_gva_to_gfn:
+                ASSERT(0);
+                /* fall through */
+            default:
+                rc = X86EMUL_UNHANDLEABLE;
+                break;
             }
+            if ( rc != X86EMUL_OKAY )
+                break;
             rc = write_handler(v, p->addr + (sign * i * p->size), p->size,
                                data);
             if ( rc != X86EMUL_OKAY )
@@ -165,8 +176,28 @@ static int process_portio_intercept(port
         for ( i = 0; i < p->count; i++ )
         {
             data = 0;
-            (void)hvm_copy_from_guest_phys(&data, p->data + sign*i*p->size,
-                                           p->size);
+            switch ( hvm_copy_from_guest_phys(&data,
+                                              p->data + sign * i * p->size,
+                                              p->size) )
+            {
+            case HVMCOPY_okay:
+                break;
+            case HVMCOPY_gfn_paged_out:
+            case HVMCOPY_gfn_shared:
+                rc = X86EMUL_RETRY;
+                break;
+            case HVMCOPY_bad_gfn_to_mfn:
+                data = ~0;
+                break;
+            case HVMCOPY_bad_gva_to_gfn:
+                ASSERT(0);
+                /* fall through */
+            default:
+                rc = X86EMUL_UNHANDLEABLE;
+                break;
+            }
+            if ( rc != X86EMUL_OKAY )
+                break;
             rc = action(IOREQ_WRITE, p->addr, p->size, &data);
             if ( rc != X86EMUL_OKAY )
                 break;
--- a/xen/arch/x86/hvm/io.c
+++ b/xen/arch/x86/hvm/io.c
@@ -340,14 +340,24 @@ static int dpci_ioport_write(uint32_t mp
         data = p->data;
         if ( p->data_is_ptr )
         {
-            int ret;
-            
-            ret = hvm_copy_from_guest_phys(&data, 
-                                           p->data + (sign * i * p->size),
-                                           p->size);
-            if ( (ret == HVMCOPY_gfn_paged_out) &&
-                 (ret == HVMCOPY_gfn_shared) )
+            switch ( hvm_copy_from_guest_phys(&data,
+                                              p->data + sign * i * p->size,
+                                              p->size) )
+            {
+            case HVMCOPY_okay:
+                break;
+            case HVMCOPY_gfn_paged_out:
+            case HVMCOPY_gfn_shared:
                 return X86EMUL_RETRY;
+            case HVMCOPY_bad_gfn_to_mfn:
+                data = ~0;
+                break;
+            case HVMCOPY_bad_gva_to_gfn:
+                ASSERT(0);
+                /* fall through */
+            default:
+                return X86EMUL_UNHANDLEABLE;
+            }
         }
 
         switch ( p->size )
--- a/xen/arch/x86/hvm/vmx/realmode.c
+++ b/xen/arch/x86/hvm/vmx/realmode.c
@@ -39,7 +39,9 @@ static void realmode_deliver_exception(
 
  again:
     last_byte = (vector * 4) + 3;
-    if ( idtr->limit < last_byte )
+    if ( idtr->limit < last_byte ||
+         hvm_copy_from_guest_phys(&cs_eip, idtr->base + vector * 4, 4) !=
+         HVMCOPY_okay )
     {
         /* Software interrupt? */
         if ( insn_len != 0 )
@@ -64,8 +66,6 @@ static void realmode_deliver_exception(
         }
     }
 
-    (void)hvm_copy_from_guest_phys(&cs_eip, idtr->base + vector * 4, 4);
-
     frame[0] = regs->eip + insn_len;
     frame[1] = csr->sel;
     frame[2] = regs->eflags & ~X86_EFLAGS_RF;