KVM: arm64: Split S1 permission evaluation into direct and hierarchical parts

The AArch64.S1DirectBasePermissions() pseudocode deals with both
direct and hierarchical S1 permission evaluation. While this is
probably convenient in the pseudocode, we would like a bit more
flexibility to slot things like indirect permissions.

To that effect, split the two permission check parts out of
handle_at_slow() and into their own functions. The permissions
are passed around as part of the walk_result structure.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241023145345.1613824-20-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

1 files changed, 98 insertions, 64 deletions

diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
index b9d0992e9197..adcfce3f67f0 100644
--- a/arch/arm64/kvm/at.c
+++ b/arch/arm64/kvm/at.c
@@ -37,6 +37,12 @@ struct s1_walk_result {
 			u8	APTable;
 			bool	UXNTable;
 			bool	PXNTable;
+			bool	ur;
+			bool	uw;
+			bool	ux;
+			bool	pr;
+			bool	pw;
+			bool	px;
 		};
 		struct {
 			u8	fst;
@@ -764,111 +770,139 @@ static bool pan3_enabled(struct kvm_vcpu *vcpu, enum trans_regime regime)
 	return sctlr & SCTLR_EL1_EPAN;
 }
 
-static u64 handle_at_slow(struct kvm_vcpu *vcpu, u32 op, u64 vaddr)
+static void compute_s1_direct_permissions(struct kvm_vcpu *vcpu,
+					  struct s1_walk_info *wi,
+					  struct s1_walk_result *wr)
 {
-	bool perm_fail, ur, uw, ux, pr, pw, px;
-	struct s1_walk_result wr = {};
-	struct s1_walk_info wi = {};
-	int ret, idx;
-
-	ret = setup_s1_walk(vcpu, op, &wi, &wr, vaddr);
-	if (ret)
-		goto compute_par;
-
-	if (wr.level == S1_MMU_DISABLED)
-		goto compute_par;
-
-	idx = srcu_read_lock(&vcpu->kvm->srcu);
-
-	ret = walk_s1(vcpu, &wi, &wr, vaddr);
-
-	srcu_read_unlock(&vcpu->kvm->srcu, idx);
-
-	if (ret)
-		goto compute_par;
-
-	/* FIXME: revisit when adding indirect permission support */
-	/* AArch64.S1DirectBasePermissions() */
-	if (wi.regime != TR_EL2) {
-		switch (FIELD_GET(PTE_USER | PTE_RDONLY, wr.desc)) {
+	/* Non-hierarchical part of AArch64.S1DirectBasePermissions() */
+	if (wi->regime != TR_EL2) {
+		switch (FIELD_GET(PTE_USER | PTE_RDONLY, wr->desc)) {
 		case 0b00:
-			pr = pw = true;
-			ur = uw = false;
+			wr->pr = wr->pw = true;
+			wr->ur = wr->uw = false;
 			break;
 		case 0b01:
-			pr = pw = ur = uw = true;
+			wr->pr = wr->pw = wr->ur = wr->uw = true;
 			break;
 		case 0b10:
-			pr = true;
-			pw = ur = uw = false;
+			wr->pr = true;
+			wr->pw = wr->ur = wr->uw = false;
 			break;
 		case 0b11:
-			pr = ur = true;
-			pw = uw = false;
+			wr->pr = wr->ur = true;
+			wr->pw = wr->uw = false;
 			break;
 		}
 
-		switch (wr.APTable) {
+		/* We don't use px for anything yet, but hey... */
+		wr->px = !((wr->desc & PTE_PXN) || wr->uw);
+		wr->ux = !(wr->desc & PTE_UXN);
+	} else {
+		wr->ur = wr->uw = wr->ux = false;
+
+		if (!(wr->desc & PTE_RDONLY)) {
+			wr->pr = wr->pw = true;
+		} else {
+			wr->pr = true;
+			wr->pw = false;
+		}
+
+		/* XN maps to UXN */
+		wr->px = !(wr->desc & PTE_UXN);
+	}
+}
+
+static void compute_s1_hierarchical_permissions(struct kvm_vcpu *vcpu,
+						struct s1_walk_info *wi,
+						struct s1_walk_result *wr)
+{
+	/* Hierarchical part of AArch64.S1DirectBasePermissions() */
+	if (wi->regime != TR_EL2) {
+		switch (wr->APTable) {
 		case 0b00:
 			break;
 		case 0b01:
-			ur = uw = false;
+			wr->ur = wr->uw = false;
 			break;
 		case 0b10:
-			pw = uw = false;
+			wr->pw = wr->uw = false;
 			break;
 		case 0b11:
-			pw = ur = uw = false;
+			wr->pw = wr->ur = wr->uw = false;
 			break;
 		}
 
-		/* We don't use px for anything yet, but hey... */
-		px = !((wr.desc & PTE_PXN) || wr.PXNTable || uw);
-		ux = !((wr.desc & PTE_UXN) || wr.UXNTable);
+		wr->px &= !wr->PXNTable;
+		wr->ux &= !wr->UXNTable;
+	} else {
+		if (wr->APTable & BIT(1))
+			wr->pw = false;
 
-		if (op == OP_AT_S1E1RP || op == OP_AT_S1E1WP) {
-			bool pan;
+		/* XN maps to UXN */
+		wr->px &= !wr->UXNTable;
+	}
+}
 
-			pan = *vcpu_cpsr(vcpu) & PSR_PAN_BIT;
-			pan &= ur || uw || (pan3_enabled(vcpu, wi.regime) && ux);
-			pw &= !pan;
-			pr &= !pan;
-		}
-	} else {
-		ur = uw = ux = false;
+static void compute_s1_permissions(struct kvm_vcpu *vcpu, u32 op,
+				   struct s1_walk_info *wi,
+				   struct s1_walk_result *wr)
+{
+	compute_s1_direct_permissions(vcpu, wi, wr);
 
-		if (!(wr.desc & PTE_RDONLY)) {
-			pr = pw = true;
-		} else {
-			pr = true;
-			pw = false;
-		}
+	if (!wi->hpd)
+		compute_s1_hierarchical_permissions(vcpu, wi, wr);
 
-		if (wr.APTable & BIT(1))
-			pw = false;
+	if (op == OP_AT_S1E1RP || op == OP_AT_S1E1WP) {
+		bool pan;
 
-		/* XN maps to UXN */
-		px = !((wr.desc & PTE_UXN) || wr.UXNTable);
+		pan = *vcpu_cpsr(vcpu) & PSR_PAN_BIT;
+		pan &= wr->ur || wr->uw || (pan3_enabled(vcpu, wi->regime) && wr->ux);
+		wr->pw &= !pan;
+		wr->pr &= !pan;
 	}
+}
+
+static u64 handle_at_slow(struct kvm_vcpu *vcpu, u32 op, u64 vaddr)
+{
+	struct s1_walk_result wr = {};
+	struct s1_walk_info wi = {};
+	bool perm_fail = false;
+	int ret, idx;
+
+	ret = setup_s1_walk(vcpu, op, &wi, &wr, vaddr);
+	if (ret)
+		goto compute_par;
+
+	if (wr.level == S1_MMU_DISABLED)
+		goto compute_par;
+
+	idx = srcu_read_lock(&vcpu->kvm->srcu);
+
+	ret = walk_s1(vcpu, &wi, &wr, vaddr);
+
+	srcu_read_unlock(&vcpu->kvm->srcu, idx);
+
+	if (ret)
+		goto compute_par;
 
-	perm_fail = false;
+	compute_s1_permissions(vcpu, op, &wi, &wr);
 
 	switch (op) {
 	case OP_AT_S1E1RP:
 	case OP_AT_S1E1R:
 	case OP_AT_S1E2R:
-		perm_fail = !pr;
+		perm_fail = !wr.pr;
 		break;
 	case OP_AT_S1E1WP:
 	case OP_AT_S1E1W:
 	case OP_AT_S1E2W:
-		perm_fail = !pw;
+		perm_fail = !wr.pw;
 		break;
 	case OP_AT_S1E0R:
-		perm_fail = !ur;
+		perm_fail = !wr.ur;
 		break;
 	case OP_AT_S1E0W:
-		perm_fail = !uw;
+		perm_fail = !wr.uw;
 		break;
 	case OP_AT_S1E1A:
 	case OP_AT_S1E2A: