[PATCH] KVM: arm64: Forward FFA_NOTIFICATION* calls to TrustZone

[PATCH] KVM: arm64: Forward FFA_NOTIFICATION* calls to TrustZone

[Sebastian Ene]

Remove the FFA_NOTIFICATION* calls from the blocklist used by the pKVM
FF-A proxy. This restriction was preventing the use of asynchronous
signaling mechanisms defined by the Arm FF-A specification to
communicate with the secure services.
While these calls are markes as optional, there is no reason why the
hypervisor proxy would block them because:

1. Host is the Sole Non-Secure Endpoint: The Host operates as the
   only Non-Secure VM ID (VM ID 0) recognized by the Secure World.
   Because all forwarded notifications are inherently attributed to
   the Host by the SPMC, there is no risk of VM ID spoofing
   originating from the Normal World.

2. No Memory Pointers or Addresses: The FFA_NOTIFICATION_* ABIs
   operate strictly via register-based parameters, passing only
   VM IDs, VCPU IDs, flags, and bitmaps. Because these calls do
   not contain memory addresses, offsets, or pointers, forwarding
   them doesn't pose a risk of memory-based confused deputy attack
   (e.g., tricking the SPMC into overwriting protected memory).

While the pKVM proxy behaves as a relayer, it doesn't currently have its
own FF-A ID(only the host has the ID 0). The behavior of the setup
flow is covered by the spec in the: '10.9 Notification support without
a Hypervisor'.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 1af722771178..a82d0cd22a17 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -675,14 +675,6 @@ static bool ffa_call_supported(u64 func_id)
 	case FFA_RXTX_MAP:
 	case FFA_MEM_DONATE:
 	case FFA_MEM_RETRIEVE_REQ:
-       /* Optional notification interfaces added in FF-A 1.1 */
-	case FFA_NOTIFICATION_BITMAP_CREATE:
-	case FFA_NOTIFICATION_BITMAP_DESTROY:
-	case FFA_NOTIFICATION_BIND:
-	case FFA_NOTIFICATION_UNBIND:
-	case FFA_NOTIFICATION_SET:
-	case FFA_NOTIFICATION_GET:
-	case FFA_NOTIFICATION_INFO_GET:
 	/* Optional interfaces added in FF-A 1.2 */
 	case FFA_MSG_SEND_DIRECT_REQ2:		/* Optional per 7.5.1 */
 	case FFA_MSG_SEND_DIRECT_RESP2:		/* Optional per 7.5.1 */
-- 
2.54.0.545.g6539524ca2-goog