[PATCH v4 0/7] KVM: arm64: Forward FFA_NOTIFICATION* calls to TrustZone

[PATCH v4 0/7] 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'.

---
Changes in v4:
- previous series(v3) had serious issues with the patch number and it
  appeared like it used a mixed bag from v2 as well. Resend this to
  restore the correct order of the patches.
- fix strict check in ffa_check_unused_args_sbz and make it "<= 17"
- check the receiver endpoint Id in
  FFA_NOTIFICATION_BIND/FFA_NOTIFICATION_UNBIND instead of the sender
- use hyp_smccc_1_2_smc all along 
- check the receiver endpoit Id when doing FFA_NOTIFICATION_GET  

Changes in v3:
- applied Will's suggestion to use the introduced method
  ffa_check_unused_args_sbz for existing calls and added a new
patch in the beggining of the series to do this.
- merged the handling of
  FFA_NOTIFICATION_BITMAP_CREATE/FFA_NOTIFICATION_BITMAP_DESTROY into
one patch as Vincent suggested and create one handler for both.

Changes in v2:
- enforce the MBZ/SBZ fields
- split the calls into separate patches
- rebase on 7.1-rc7

Link to v3:
https://lore.kernel.org/all/20260616105417.2578670-1-sebastianene@google.com/
Link to v2:
https://lore.kernel.org/all/20260608165549.1479409-1-sebastianene@google.com/
Link to v1:
https://lore.kernel.org/all/20260501114447.2389222-2-sebastianene@google.com/

Sebastian Ene (7):
  KVM: arm64: Enforce strict SBZ checks in the FF-A proxy
  KVM: arm64: Forward FFA_NOTIFICATION_BITMAP calls to Trustzone
  KVM: arm64: Support FFA_NOTIFICATION_BIND in host handler
  KVM: arm64: Support FFA_NOTIFICATION_UNBIND in host handler
  KVM: arm64: Support FFA_NOTIFICATION_SET in host handler
  KVM: arm64: Support FFA_NOTIFICATION_GET in host handler
  KVM: arm64: Support FFA_NOTIFICATION_INFO_GET in host handler

 arch/arm64/kvm/hyp/nvhe/ffa.c | 211 ++++++++++++++++++++++++++++++++--
 1 file changed, 203 insertions(+), 8 deletions(-)

-- 
2.54.0.1136.gdb2ca164c4-goog

[PATCH v4 1/7] KVM: arm64: Enforce strict SBZ checks in the FF-A proxy

[Sebastian Ene]

Introduce a helper method ffa_check_unused_args_sbz to enforce strict
arguments checking when the hypervisor acts as a relayer between the
host and Trustzone.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 47 +++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 1af722771178..c64c704f22f8 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -71,6 +71,18 @@ static u32 hyp_ffa_version;
 static bool has_version_negotiated;
 static hyp_spinlock_t version_lock;
 
+static bool ffa_check_unused_args_sbz(struct kvm_cpu_context *ctxt, int first_reg)
+{
+	int reg;
+
+	for (reg = first_reg; reg <= 17; reg++) {
+		if (cpu_reg(ctxt, reg))
+			return true;
+	}
+
+	return false;
+}
+
 static void ffa_to_smccc_error(struct arm_smccc_1_2_regs *res, u64 ffa_errno)
 {
 	*res = (struct arm_smccc_1_2_regs) {
@@ -239,6 +251,11 @@ static void do_ffa_rxtx_map(struct arm_smccc_1_2_regs *res,
 	int ret = 0;
 	void *rx_virt, *tx_virt;
 
+	if (ffa_check_unused_args_sbz(ctxt, 4)) {
+		ret = FFA_RET_INVALID_PARAMETERS;
+		goto out;
+	}
+
 	if (npages != (KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE) / FFA_PAGE_SIZE) {
 		ret = FFA_RET_INVALID_PARAMETERS;
 		goto out;
@@ -315,6 +332,11 @@ static void do_ffa_rxtx_unmap(struct arm_smccc_1_2_regs *res,
 	DECLARE_REG(u32, id, ctxt, 1);
 	int ret = 0;
 
+	if (ffa_check_unused_args_sbz(ctxt, 2)) {
+		ret = FFA_RET_INVALID_PARAMETERS;
+		goto out;
+	}
+
 	if (id != HOST_FFA_ID) {
 		ret = FFA_RET_INVALID_PARAMETERS;
 		goto out;
@@ -421,6 +443,11 @@ static void do_ffa_mem_frag_tx(struct arm_smccc_1_2_regs *res,
 	int ret = FFA_RET_INVALID_PARAMETERS;
 	u32 nr_ranges;
 
+	if (ffa_check_unused_args_sbz(ctxt, 5)) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
 	if (fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE)
 		goto out;
 
@@ -482,6 +509,11 @@ static void __do_ffa_mem_xfer(const u64 func_id,
 	u32 offset, nr_ranges, checked_offset;
 	int ret = 0;
 
+	if (ffa_check_unused_args_sbz(ctxt, 5)) {
+		ret = FFA_RET_INVALID_PARAMETERS;
+		goto out;
+	}
+
 	if (addr_mbz || npages_mbz || fraglen > len ||
 	    fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE) {
 		ret = FFA_RET_INVALID_PARAMETERS;
@@ -581,6 +613,11 @@ static void do_ffa_mem_reclaim(struct arm_smccc_1_2_regs *res,
 	int ret = 0;
 	u64 handle;
 
+	if (ffa_check_unused_args_sbz(ctxt, 4)) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
 	handle = PACK_HANDLE(handle_lo, handle_hi);
 
 	hyp_spin_lock(&host_buffers.lock);
@@ -769,6 +806,11 @@ static void do_ffa_version(struct arm_smccc_1_2_regs *res,
 {
 	DECLARE_REG(u32, ffa_req_version, ctxt, 1);
 
+	if (ffa_check_unused_args_sbz(ctxt, 2)) {
+		res->a0 = FFA_RET_NOT_SUPPORTED;
+		return;
+	}
+
 	if (FFA_MAJOR_VERSION(ffa_req_version) != 1) {
 		res->a0 = FFA_RET_NOT_SUPPORTED;
 		return;
@@ -818,6 +860,11 @@ static void do_ffa_part_get(struct arm_smccc_1_2_regs *res,
 	DECLARE_REG(u32, flags, ctxt, 5);
 	u32 count, partition_sz, copy_sz;
 
+	if (ffa_check_unused_args_sbz(ctxt, 6)) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
 	hyp_spin_lock(&host_buffers.lock);
 	if (!host_buffers.rx) {
 		ffa_to_smccc_res(res, FFA_RET_BUSY);
-- 
2.54.0.1136.gdb2ca164c4-goog

[PATCH v4 2/7] KVM: arm64: Forward FFA_NOTIFICATION_BITMAP calls to Trustzone

[Sebastian Ene]

Allow FF-A notification bitmap messages to be forwarded to
Trustzone from the host kernel driver enforce checking for
SBZ fields.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index c64c704f22f8..a72f6d4b62f0 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -713,8 +713,6 @@ static bool ffa_call_supported(u64 func_id)
 	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:
@@ -909,6 +907,27 @@ static void do_ffa_part_get(struct arm_smccc_1_2_regs *res,
 	hyp_spin_unlock(&host_buffers.lock);
 }
 
+static void do_ffa_notif_bitmap(struct arm_smccc_1_2_regs *res,
+				struct kvm_cpu_context *ctxt)
+{
+	DECLARE_REG(u32, func_id, ctxt, 0);
+	DECLARE_REG(u32, vmid, ctxt, 1);
+	struct arm_smccc_1_2_regs *args;
+
+	if (ffa_check_unused_args_sbz(ctxt, func_id == FFA_NOTIFICATION_BITMAP_CREATE ? 3 : 2)) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	if (vmid != HOST_FFA_ID) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	args = (void *)&ctxt->regs.regs[0];
+	hyp_smccc_1_2_smc(args, res);
+}
+
 bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 {
 	struct arm_smccc_1_2_regs res;
@@ -967,6 +986,10 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 	case FFA_PARTITION_INFO_GET:
 		do_ffa_part_get(&res, host_ctxt);
 		goto out_handled;
+	case FFA_NOTIFICATION_BITMAP_CREATE:
+	case FFA_NOTIFICATION_BITMAP_DESTROY:
+		do_ffa_notif_bitmap(&res, host_ctxt);
+		goto out_handled;
 	}
 
 	if (ffa_call_supported(func_id))
-- 
2.54.0.1136.gdb2ca164c4-goog

[PATCH v4 3/7] KVM: arm64: Support FFA_NOTIFICATION_BIND in host handler

[Sebastian Ene]

Verify the arguments of the FF-A notification bind call and forward the
message to Trustzone.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index a72f6d4b62f0..1f38ad008675 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -42,6 +42,8 @@
  */
 #define HOST_FFA_ID	0
 
+#define FFA_NOTIF_RECEIVER_ENDP_MASK	GENMASK(15, 0)
+
 /*
  * A buffer to hold the maximum descriptor size we can see from the host,
  * which is required when the SPMD returns a fragmented FFA_MEM_RETRIEVE_RESP
@@ -713,7 +715,6 @@ static bool ffa_call_supported(u64 func_id)
 	case FFA_MEM_DONATE:
 	case FFA_MEM_RETRIEVE_REQ:
        /* Optional notification interfaces added in FF-A 1.1 */
-	case FFA_NOTIFICATION_BIND:
 	case FFA_NOTIFICATION_UNBIND:
 	case FFA_NOTIFICATION_SET:
 	case FFA_NOTIFICATION_GET:
@@ -928,6 +929,32 @@ static void do_ffa_notif_bitmap(struct arm_smccc_1_2_regs *res,
 	hyp_smccc_1_2_smc(args, res);
 }
 
+static void do_ffa_notif_bind(struct arm_smccc_1_2_regs *res,
+			      struct kvm_cpu_context *ctxt)
+{
+	DECLARE_REG(u32, endp_id, ctxt, 1);
+	DECLARE_REG(u32, flags, ctxt, 2);
+	struct arm_smccc_1_2_regs *args;
+
+	if (ffa_check_unused_args_sbz(ctxt, 5)) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	if (FIELD_GET(FFA_NOTIF_RECEIVER_ENDP_MASK, endp_id) != HOST_FFA_ID) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	if (flags > 1) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	args = (void *)&ctxt->regs.regs[0];
+	hyp_smccc_1_2_smc(args, res);
+}
+
 bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 {
 	struct arm_smccc_1_2_regs res;
@@ -990,6 +1017,9 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 	case FFA_NOTIFICATION_BITMAP_DESTROY:
 		do_ffa_notif_bitmap(&res, host_ctxt);
 		goto out_handled;
+	case FFA_NOTIFICATION_BIND:
+		do_ffa_notif_bind(&res, host_ctxt);
+		goto out_handled;
 	}
 
 	if (ffa_call_supported(func_id))
-- 
2.54.0.1136.gdb2ca164c4-goog

[PATCH v4 4/7] KVM: arm64: Support FFA_NOTIFICATION_UNBIND in host handler

[Sebastian Ene]

Verify the arguments of the FF-A notification unbind call and forward
the message to Trustzone.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 1f38ad008675..adf8680f3266 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -715,7 +715,6 @@ static bool ffa_call_supported(u64 func_id)
 	case FFA_MEM_DONATE:
 	case FFA_MEM_RETRIEVE_REQ:
        /* Optional notification interfaces added in FF-A 1.1 */
-	case FFA_NOTIFICATION_UNBIND:
 	case FFA_NOTIFICATION_SET:
 	case FFA_NOTIFICATION_GET:
 	case FFA_NOTIFICATION_INFO_GET:
@@ -955,6 +954,27 @@ static void do_ffa_notif_bind(struct arm_smccc_1_2_regs *res,
 	hyp_smccc_1_2_smc(args, res);
 }
 
+static void do_ffa_notif_unbind(struct arm_smccc_1_2_regs *res,
+				struct kvm_cpu_context *ctxt)
+{
+	DECLARE_REG(u32, endp_id, ctxt, 1);
+	DECLARE_REG(u32, reserved, ctxt, 2);
+	struct arm_smccc_1_2_regs *args;
+
+	if (ffa_check_unused_args_sbz(ctxt, 5) || reserved) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	if (FIELD_GET(FFA_NOTIF_RECEIVER_ENDP_MASK, endp_id) != HOST_FFA_ID) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	args = (void *)&ctxt->regs.regs[0];
+	hyp_smccc_1_2_smc(args, res);
+}
+
 bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 {
 	struct arm_smccc_1_2_regs res;
@@ -1020,6 +1040,9 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 	case FFA_NOTIFICATION_BIND:
 		do_ffa_notif_bind(&res, host_ctxt);
 		goto out_handled;
+	case FFA_NOTIFICATION_UNBIND:
+		do_ffa_notif_unbind(&res, host_ctxt);
+		goto out_handled;
 	}
 
 	if (ffa_call_supported(func_id))
-- 
2.54.0.1136.gdb2ca164c4-goog

[PATCH v4 5/7] KVM: arm64: Support FFA_NOTIFICATION_SET in host handler

[Sebastian Ene]

Allow FF-A notification SET messages to be proxied from the pKVM
hypervisor to Trustzone and enforce MBZ/SBZ fields.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index adf8680f3266..fdf1e5fb6726 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -43,6 +43,7 @@
 #define HOST_FFA_ID	0
 
 #define FFA_NOTIF_RECEIVER_ENDP_MASK	GENMASK(15, 0)
+#define FFA_NOTIF_SENDER_ENDP_MASK	GENMASK(31, 16)
 
 /*
  * A buffer to hold the maximum descriptor size we can see from the host,
@@ -715,7 +716,6 @@ static bool ffa_call_supported(u64 func_id)
 	case FFA_MEM_DONATE:
 	case FFA_MEM_RETRIEVE_REQ:
        /* Optional notification interfaces added in FF-A 1.1 */
-	case FFA_NOTIFICATION_SET:
 	case FFA_NOTIFICATION_GET:
 	case FFA_NOTIFICATION_INFO_GET:
 	/* Optional interfaces added in FF-A 1.2 */
@@ -975,6 +975,32 @@ static void do_ffa_notif_unbind(struct arm_smccc_1_2_regs *res,
 	hyp_smccc_1_2_smc(args, res);
 }
 
+static void do_ffa_notif_set(struct arm_smccc_1_2_regs *res,
+			     struct kvm_cpu_context *ctxt)
+{
+	DECLARE_REG(u32, endp_id, ctxt, 1);
+	DECLARE_REG(u32, flags, ctxt, 2);
+	struct arm_smccc_1_2_regs *args;
+
+	if (FIELD_GET(FFA_NOTIF_SENDER_ENDP_MASK, endp_id) != HOST_FFA_ID) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	if (ffa_check_unused_args_sbz(ctxt, 5)) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	if (flags & GENMASK(15, 2)) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	args = (void *)&ctxt->regs.regs[0];
+	hyp_smccc_1_2_smc(args, res);
+}
+
 bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 {
 	struct arm_smccc_1_2_regs res;
@@ -1043,6 +1069,9 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 	case FFA_NOTIFICATION_UNBIND:
 		do_ffa_notif_unbind(&res, host_ctxt);
 		goto out_handled;
+	case FFA_NOTIFICATION_SET:
+		do_ffa_notif_set(&res, host_ctxt);
+		goto out_handled;
 	}
 
 	if (ffa_call_supported(func_id))
-- 
2.54.0.1136.gdb2ca164c4-goog

[PATCH v4 6/7] KVM: arm64: Support FFA_NOTIFICATION_GET in host handler

[Sebastian Ene]

Allow FF-A notification GET messages to be proxied from the pKVM
hypervisor to Trustzone and enforce MBZ/SBZ fields.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index fdf1e5fb6726..de4794338388 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -716,7 +716,6 @@ static bool ffa_call_supported(u64 func_id)
 	case FFA_MEM_DONATE:
 	case FFA_MEM_RETRIEVE_REQ:
        /* Optional notification interfaces added in FF-A 1.1 */
-	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 */
@@ -1001,6 +1000,32 @@ static void do_ffa_notif_set(struct arm_smccc_1_2_regs *res,
 	hyp_smccc_1_2_smc(args, res);
 }
 
+static void do_ffa_notif_get(struct arm_smccc_1_2_regs *res,
+			     struct kvm_cpu_context *ctxt)
+{
+	DECLARE_REG(u32, endp_id, ctxt, 1);
+	DECLARE_REG(u32, flags, ctxt, 2);
+	struct arm_smccc_1_2_regs *args;
+
+	if (FIELD_GET(FFA_NOTIF_RECEIVER_ENDP_MASK, endp_id) != HOST_FFA_ID) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	if (ffa_check_unused_args_sbz(ctxt, 3)) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	if (flags & GENMASK(31, 4)) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	args = (void *)&ctxt->regs.regs[0];
+	hyp_smccc_1_2_smc(args, res);
+}
+
 bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 {
 	struct arm_smccc_1_2_regs res;
@@ -1072,6 +1097,9 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 	case FFA_NOTIFICATION_SET:
 		do_ffa_notif_set(&res, host_ctxt);
 		goto out_handled;
+	case FFA_NOTIFICATION_GET:
+		do_ffa_notif_get(&res, host_ctxt);
+		goto out_handled;
 	}
 
 	if (ffa_call_supported(func_id))
-- 
2.54.0.1136.gdb2ca164c4-goog

[PATCH v4 7/7] KVM: arm64: Support FFA_NOTIFICATION_INFO_GET in host handler

[Sebastian Ene]

Allow the host to query the FF-A notifiction status and proxy the info
get message to Trustzone. Make sure that the SBZ fields are enforced.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index de4794338388..ffb6d44b5010 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -715,8 +715,6 @@ 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_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 */
@@ -1026,6 +1024,20 @@ static void do_ffa_notif_get(struct arm_smccc_1_2_regs *res,
 	hyp_smccc_1_2_smc(args, res);
 }
 
+static void do_ffa_notif_info_get(struct arm_smccc_1_2_regs *res,
+				  struct kvm_cpu_context *ctxt)
+{
+	struct arm_smccc_1_2_regs *args;
+
+	if (ffa_check_unused_args_sbz(ctxt, 1)) {
+		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
+		return;
+	}
+
+	args = (void *)&ctxt->regs.regs[0];
+	hyp_smccc_1_2_smc(args, res);
+}
+
 bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 {
 	struct arm_smccc_1_2_regs res;
@@ -1100,6 +1112,9 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 	case FFA_NOTIFICATION_GET:
 		do_ffa_notif_get(&res, host_ctxt);
 		goto out_handled;
+	case FFA_NOTIFICATION_INFO_GET:
+		do_ffa_notif_info_get(&res, host_ctxt);
+		goto out_handled;
 	}
 
 	if (ffa_call_supported(func_id))
-- 
2.54.0.1136.gdb2ca164c4-goog

Re: [PATCH v4 5/7] KVM: arm64: Support FFA_NOTIFICATION_SET in host handler

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The MBZ (Must Be Zero) check for the `flags` parameter (W2) in `do_ffa_notif_set` uses an incorrect mask, leaving bits [31:16] completely unvalidated.
--

commit 18c05e4ad6759f3bb72be1916c4e1abac54bcb30
Author: Sebastian Ene <sebastianene@google.com>

KVM: arm64: Support FFA_NOTIFICATION_SET in host handler

This commit adds support for proxying FF-A notification SET messages from the
pKVM hypervisor to TrustZone. It introduces validation to enforce MBZ and SBZ
fields before forwarding the call.

> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index adf8680f32663..fdf1e5fb67267 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c

[ ... ]

> @@ -975,6 +975,32 @@ static void do_ffa_notif_unbind(struct arm_smccc_1_2_regs *res,
>  	hyp_smccc_1_2_smc(args, res);
>  }
>  
> +static void do_ffa_notif_set(struct arm_smccc_1_2_regs *res,
> +			     struct kvm_cpu_context *ctxt)
> +{
> +	DECLARE_REG(u32, endp_id, ctxt, 1);
> +	DECLARE_REG(u32, flags, ctxt, 2);
> +	struct arm_smccc_1_2_regs *args;
> +
> +	if (FIELD_GET(FFA_NOTIF_SENDER_ENDP_MASK, endp_id) != HOST_FFA_ID) {
> +		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
> +		return;
> +	}
> +
> +	if (ffa_check_unused_args_sbz(ctxt, 5)) {
> +		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
> +		return;
> +	}
> +
> +	if (flags & GENMASK(15, 2)) {
[Severity: Medium]
Does this mask properly validate all reserved bits?

The FF-A specification dictates that for the FFA_NOTIFICATION_SET interface,
bits 31 through 2 of the flags parameter passed in W2 are reserved and must
be zero. By using GENMASK(15, 2), the upper 16 bits of the 32-bit flags
variable are completely ignored.

Can this allow a malicious or buggy host to pass non-zero upper bits that
silently bypass validation and get proxied to EL3?

> +		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
> +		return;
> +	}
> +
> +	args = (void *)&ctxt->regs.regs[0];
> +	hyp_smccc_1_2_smc(args, res);
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260616154149.2763214-1-sebastianene@google.com?part=5

Re: [PATCH v4 2/7] KVM: arm64: Forward FFA_NOTIFICATION_BITMAP calls to Trustzone

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The FFA_NOTIFICATION_BITMAP_CREATE handler fails to enforce SBZ/MBZ checks on the upper bits of the w2 register.
--

commit d7fbb4e364c5dfed4241ae740e49c01e3b35077f
Author: Sebastian Ene <sebastianene@google.com>

KVM: arm64: Forward FFA_NOTIFICATION_BITMAP calls to Trustzone

This commit allows FF-A notification bitmap messages to be forwarded to
Trustzone from the host kernel driver. It also intends to enforce checking
for SBZ (Should Be Zero) fields.

> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c

[ ... ]

> @@ -909,6 +907,27 @@ static void do_ffa_part_get(struct arm_smccc_1_2_regs *res,
>  	hyp_spin_unlock(&host_buffers.lock);
>  }
>  
> +static void do_ffa_notif_bitmap(struct arm_smccc_1_2_regs *res,
> +				struct kvm_cpu_context *ctxt)
> +{
> +	DECLARE_REG(u32, func_id, ctxt, 0);
> +	DECLARE_REG(u32, vmid, ctxt, 1);
> +	struct arm_smccc_1_2_regs *args;
> +
> +	if (ffa_check_unused_args_sbz(ctxt, func_id == FFA_NOTIFICATION_BITMAP_CREATE ? 3 : 2)) {

[Severity: Medium]
The commit message mentions enforcing checks for SBZ fields. For the
FFA_NOTIFICATION_BITMAP_CREATE call, the w2 register contains the
vcpu_count in bits [15:0], while bits [31:16] are defined as MBZ
(Must Be Zero) by the FF-A specification.

While ffa_check_unused_args_sbz() correctly verifies that fully unused
registers (w3-w17) are zero, does this miss validating the upper 16 bits
of the partially-used w2 register before it is passed to TrustZone?

> +		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
> +		return;
> +	}
> +
> +	if (vmid != HOST_FFA_ID) {
> +		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
> +		return;
> +	}
> +
> +	args = (void *)&ctxt->regs.regs[0];
> +	hyp_smccc_1_2_smc(args, res);
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260616154149.2763214-1-sebastianene@google.com?part=2

Re: [PATCH v4 1/7] KVM: arm64: Enforce strict SBZ checks in the FF-A proxy

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:

New issues:
- [High] `ffa_check_unused_args_sbz` incorrectly checks preserved registers and the upper 32 bits of parameter registers for SMC32 calls, causing spurious rejections.
- [Low] Missing strict SBZ validation for `FFA_FEATURES`.

Pre-existing issues:
- [Critical] Parser differential between KVM (EL2) and SPMD (EL3) regarding the `ep_mem_offset` field allows the host to bypass pKVM memory isolation.
- [High] Uninitialized EL2 stack memory is leaked to the EL1 host in `do_ffa_version`.
--

commit 5972f4c57539fa5e01e7e9c49f62766ed5e85d37
Author: Sebastian Ene <sebastianene@google.com>

KVM: arm64: Enforce strict SBZ checks in the FF-A proxy

Introduce a helper method ffa_check_unused_args_sbz to enforce strict
arguments checking when the hypervisor acts as a relayer between the
host and Trustzone.

> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index 1af722771178a..c64c704f22f8d 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -71,6 +71,18 @@ static u32 hyp_ffa_version;
>  static bool has_version_negotiated;
>  static hyp_spinlock_t version_lock;
>  
> +static bool ffa_check_unused_args_sbz(struct kvm_cpu_context *ctxt, int first_reg)
> +{
> +	int reg;
> +
> +	for (reg = first_reg; reg <= 17; reg++) {
> +		if (cpu_reg(ctxt, reg))
> +			return true;
> +	}
> +
> +	return false;
> +}
> +

[Severity: High]
Does this loop incorrectly check preserved registers and the upper 32 bits
of parameter registers for SMC32 calls?

According to the SMCCC ABI, SMC32 calls pass parameters in W0-W7, while
X8-X17 are caller-saved preserved registers. The caller does not need to
zero X8-X17, and the upper 32 bits of X0-X7 are architecturally unknown.
Checking these bits using cpu_reg(), which reads the full 64-bit value,
could cause KVM to spuriously reject perfectly valid, spec-compliant SMC32
calls (such as FFA_VERSION and FFA_PARTITION_INFO_GET) if the host or guest
has application data in those registers.

[Severity: Low]
Is the ffa_check_unused_args_sbz() check missing from do_ffa_features()?

According to the FF-A specification (v1.1, section 13.2), parameters W2-W7
for FFA_FEATURES are MBZ. Since this patch introduces strict validation for
other handlers, should do_ffa_features() also enforce this check to prevent
the host from sending garbage in the unused registers?

[ ... ]

> @@ -482,6 +509,11 @@ static void __do_ffa_mem_xfer(const u64 func_id,
>  	u32 offset, nr_ranges, checked_offset;
>  	int ret = 0;
>  
> +	if (ffa_check_unused_args_sbz(ctxt, 5)) {
> +		ret = FFA_RET_INVALID_PARAMETERS;
> +		goto out;
> +	}
> +

[Severity: Critical]
This is a pre-existing issue, but is there a parser differential between
KVM (EL2) and SPMD (EL3) regarding the ep_mem_offset field?

In __do_ffa_mem_xfer(), KVM uses ffa_mem_desc_offset() to locate the
endpoint memory access descriptor:

ep_mem_access = (void *)buf + ffa_mem_desc_offset(buf, 0, hyp_ffa_version);

For FF-A v1.1, this helper statically returns sizeof(struct ffa_mem_region)
and ignores the host-provided buf->ep_mem_offset field. However, SPMD (EL3)
parses the unmodified buffer forwarded by KVM and honors buf->ep_mem_offset.

Could a malicious host set buf->ep_mem_offset to a large value, place a
benign descriptor at the static offset KVM checks, and a malicious
descriptor at the SPMD offset, thereby bypassing KVM's isolation?

[ ... ]

> @@ -769,6 +806,11 @@ static void do_ffa_version(struct arm_smccc_1_2_regs *res,
>  {
>  	DECLARE_REG(u32, ffa_req_version, ctxt, 1);
>  
> +	if (ffa_check_unused_args_sbz(ctxt, 2)) {
> +		res->a0 = FFA_RET_NOT_SUPPORTED;
> +		return;
> +	}
> +

[Severity: High]
This isn't a bug introduced by this patch, but does returning directly here
leak uninitialized EL2 stack memory to the EL1 host?

In kvm_host_ffa_handler(), struct arm_smccc_1_2_regs res is declared on the
stack without zero-initialization. If this SBZ check fails, the handler
assigns res->a0 and returns immediately without using ffa_to_smccc_res()
(which zeroes the rest of the structure).

Since kvm_host_ffa_handler() then copies all 18 registers into the host's
CPU context:

cpu_reg(ctxt, 17) = res->a17;

does this allow the host to actively trigger a leak of sensitive EL2 stack
memory by supplying non-zero unused arguments?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260616154149.2763214-1-sebastianene@google.com?part=1

Re: [PATCH v4 7/7] KVM: arm64: Support FFA_NOTIFICATION_INFO_GET in host handler

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The 64-bit variant of `FFA_NOTIFICATION_INFO_GET` (`FFA_FN64_NOTIFICATION_INFO_GET`) is not intercepted, allowing the host to bypass the newly added SBZ enforcement.
--

commit 9394d3f8c8ebd222066a0b0a791f85587bdb9eb5
Author: Sebastian Ene <sebastianene@google.com>

KVM: arm64: Support FFA_NOTIFICATION_INFO_GET in host handler

Allow the host to query the FF-A notifiction status and proxy the info
get message to Trustzone. Make sure that the SBZ fields are enforced.

> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index de47943383883..ffb6d44b5010d 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
[ ... ]
> @@ -1100,6 +1112,9 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
>  	case FFA_NOTIFICATION_GET:
>  		do_ffa_notif_get(&res, host_ctxt);
>  		goto out_handled;
> +	case FFA_NOTIFICATION_INFO_GET:
> +		do_ffa_notif_info_get(&res, host_ctxt);
> +		goto out_handled;

[Severity: Medium]
Does this miss the 64-bit variant (FFA_FN64_NOTIFICATION_INFO_GET)?

If the host natively issues the 64-bit SMC ID, it will fall through this
switch statement. It will then be evaluated by ffa_call_supported(), which
returns true because it is not explicitly blocked. This causes the unvalidated
call to be passed directly through to EL3, bypassing the newly added SBZ
validation entirely.

Should FFA_FN64_NOTIFICATION_INFO_GET be handled here alongside the
32-bit variant to ensure the validation is enforced for both?

>  	}
>  
>  	if (ffa_call_supported(func_id))

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260616154149.2763214-1-sebastianene@google.com?part=7

Re: [PATCH v4 0/7] KVM: arm64: Forward FFA_NOTIFICATION* calls to TrustZone

[Vincent Donnefort]

On Tue, Jun 16, 2026 at 03:41:42PM +0000, Sebastian Ene wrote:
> 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'.

For the whole series:

Reviewed-by: Vincent Donnefort <vdonnefort@google.com>

> 
> ---
> Changes in v4:
> - previous series(v3) had serious issues with the patch number and it
>   appeared like it used a mixed bag from v2 as well. Resend this to
>   restore the correct order of the patches.
> - fix strict check in ffa_check_unused_args_sbz and make it "<= 17"
> - check the receiver endpoint Id in
>   FFA_NOTIFICATION_BIND/FFA_NOTIFICATION_UNBIND instead of the sender
> - use hyp_smccc_1_2_smc all along 
> - check the receiver endpoit Id when doing FFA_NOTIFICATION_GET  
> 
> Changes in v3:
> - applied Will's suggestion to use the introduced method
>   ffa_check_unused_args_sbz for existing calls and added a new
> patch in the beggining of the series to do this.
> - merged the handling of
>   FFA_NOTIFICATION_BITMAP_CREATE/FFA_NOTIFICATION_BITMAP_DESTROY into
> one patch as Vincent suggested and create one handler for both.
> 
> Changes in v2:
> - enforce the MBZ/SBZ fields
> - split the calls into separate patches
> - rebase on 7.1-rc7
> 
> Link to v3:
> https://lore.kernel.org/all/20260616105417.2578670-1-sebastianene@google.com/
> Link to v2:
> https://lore.kernel.org/all/20260608165549.1479409-1-sebastianene@google.com/
> Link to v1:
> https://lore.kernel.org/all/20260501114447.2389222-2-sebastianene@google.com/
> 
> Sebastian Ene (7):
>   KVM: arm64: Enforce strict SBZ checks in the FF-A proxy
>   KVM: arm64: Forward FFA_NOTIFICATION_BITMAP calls to Trustzone
>   KVM: arm64: Support FFA_NOTIFICATION_BIND in host handler
>   KVM: arm64: Support FFA_NOTIFICATION_UNBIND in host handler
>   KVM: arm64: Support FFA_NOTIFICATION_SET in host handler
>   KVM: arm64: Support FFA_NOTIFICATION_GET in host handler
>   KVM: arm64: Support FFA_NOTIFICATION_INFO_GET in host handler
> 
>  arch/arm64/kvm/hyp/nvhe/ffa.c | 211 ++++++++++++++++++++++++++++++++--
>  1 file changed, 203 insertions(+), 8 deletions(-)
> 
> -- 
> 2.54.0.1136.gdb2ca164c4-goog
>