[Xen-devel] [PATCH 1/5] x86/hvm: Switch hvm_allow_get_param() to use a whitelist

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

There are holes in the HVM_PARAM space, some of which are from deprecated
parameters, but toolstack and device models currently have blanket read
access.

Rearrange hvm_allow_get_param() to have a whitelist of toolstack-readable
parameters, with the default case failing with -EINVAL (which subsumes the
HVM_NR_PARAMS check).

No expected change for the defined, in-use params.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
---
 xen/arch/x86/hvm/hvm.c | 38 ++++++++++++++++++++++++++++----------
 1 file changed, 28 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index c22bf0b..96a6323 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4350,7 +4350,7 @@ static int hvm_allow_get_param(struct domain *d,
 
     switch ( a->index )
     {
-    /* The following parameters can be read by the guest. */
+        /* The following parameters can be read by the guest and toolstack. */
     case HVM_PARAM_CALLBACK_IRQ:
     case HVM_PARAM_VM86_TSS:
     case HVM_PARAM_VM86_TSS_SIZED:
@@ -4363,18 +4363,39 @@ static int hvm_allow_get_param(struct domain *d,
     case HVM_PARAM_ALTP2M:
     case HVM_PARAM_X87_FIP_WIDTH:
         break;
-    /*
-     * The following parameters must not be read by the guest
-     * since the domain may need to be paused.
-     */
+
+        /*
+         * The following parameters are intended for toolstack usage only.
+         * Some require the domain to be paused, and therefore may not read by
+         * the domain.
+         */
+    case HVM_PARAM_PAE_ENABLED:
     case HVM_PARAM_IOREQ_PFN:
     case HVM_PARAM_BUFIOREQ_PFN:
     case HVM_PARAM_BUFIOREQ_EVTCHN:
-    /* The remaining parameters should not be read by the guest. */
-    default:
+    case HVM_PARAM_VIRIDIAN:
+    case HVM_PARAM_TIMER_MODE:
+    case HVM_PARAM_HPET_ENABLED:
+    case HVM_PARAM_IDENT_PT:
+    case HVM_PARAM_DM_DOMAIN:
+    case HVM_PARAM_ACPI_S_STATE:
+    case HVM_PARAM_VPT_ALIGN:
+    case HVM_PARAM_NESTEDHVM:
+    case HVM_PARAM_PAGING_RING_PFN:
+    case HVM_PARAM_MONITOR_RING_PFN:
+    case HVM_PARAM_SHARING_RING_PFN:
+    case HVM_PARAM_TRIPLE_FAULT_REASON:
+    case HVM_PARAM_IOREQ_SERVER_PFN:
+    case HVM_PARAM_NR_IOREQ_SERVER_PAGES:
+    case HVM_PARAM_MCA_CAP:
         if ( d == current->domain )
             rc = -EPERM;
         break;
+
+        /* Hole, deprecated, or out-of-range. */
+    default:
+        rc = -EINVAL;
+        break;
     }
 
     return rc;
@@ -4390,9 +4411,6 @@ static int hvmop_get_param(
     if ( copy_from_guest(&a, arg, 1) )
         return -EFAULT;
 
-    if ( a.index >= HVM_NR_PARAMS )
-        return -EINVAL;
-
     d = rcu_lock_domain_by_any_id(a.domid);
     if ( d == NULL )
         return -ESRCH;
-- 
2.1.4


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