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

[Sebastian Ene <sebastianene@google.com>]

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