[xen stable-4.12] x86/hvm: simplify hvm_physdev_op allowance control

[patchbot@xxxxxxx]

commit d461833db80825829dcac7ecc50b9eb485937c0b
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Thu May 7 14:56:56 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu May 7 14:56:56 2020 +0200

    x86/hvm: simplify hvm_physdev_op allowance control
    
    PVHv1 dom0 was given access to all PHYSDEVOP hypercalls, and such
    restriction was not removed when PVHv1 code was removed. As a result
    the switch in hvm_physdev_op was more complicated than required, and
    relied on PVHv2 dom0 not having PIRQ support in order to prevent
    access to some PV specific PHYSDEVOPs.
    
    Fix this by moving the default case to the bottom of the switch, since
    there's no need for any fall through now. Also remove the hardware
    domain check, as all the not explicitly listed PHYSDEVOPs are
    forbidden for HVM domains.
    
    Finally tighten the condition to allow usage of
    PHYSDEVOP_pci_mmcfg_reserved: apart from having vPCI enabled it should
    only be used by the hardware domain. Note that the code in
    do_physdev_op is already restricting the call to privileged domains
    only, but it can be further restricted to the hardware domain only, as
    other privileged domains don't have access to MMCFG regions anyway.
    
    Overall no functional change should arise from this change.
    
    Reported-by: Julien Grall <jgrall@xxxxxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: a00e3737e085ebc1f313e36b188d4958e939e531
    master date: 2020-05-05 09:52:28 +0200
---
 xen/arch/x86/hvm/hypercall.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/hvm/hypercall.c b/xen/arch/x86/hvm/hypercall.c
index 7fcfc92b39..d66c8c3a6e 100644
--- a/xen/arch/x86/hvm/hypercall.c
+++ b/xen/arch/x86/hvm/hypercall.c
@@ -75,26 +75,26 @@ static long hvm_grant_table_op(
 static long hvm_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
 {
     const struct vcpu *curr = current;
+    const struct domain *currd = curr->domain;
 
     switch ( cmd )
     {
-    default:
-        if ( !is_hardware_domain(curr->domain) )
-            return -ENOSYS;
-        /* fall through */
     case PHYSDEVOP_map_pirq:
     case PHYSDEVOP_unmap_pirq:
     case PHYSDEVOP_eoi:
     case PHYSDEVOP_irq_status_query:
     case PHYSDEVOP_get_free_pirq:
-        if ( !has_pirq(curr->domain) )
+        if ( !has_pirq(currd) )
             return -ENOSYS;
         break;
 
     case PHYSDEVOP_pci_mmcfg_reserved:
-        if ( !has_vpci(curr->domain) )
+        if ( !has_vpci(currd) || !is_hardware_domain(currd) )
             return -ENOSYS;
         break;
+
+    default:
+        return -ENOSYS;
     }
 
     if ( !curr->hcall_compat )
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12