KVM: arm64: Handle WXN attribute

Until now, we didn't really care about WXN as it didn't have an
effect on the R/W permissions (only the execution could be droppped),
and therefore not of interest for AT.

However, with S1POE, WXN can revoke the Write permission if an
overlay is active and that execution is allowed. This *is* relevant
to AT.

Add full handling of WXN so that we correctly handle this case.

Signed-off-by: Marc Zyngier <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Oliver Upton <[email protected]>

Author: Marc Zyngier

arch/arm64/kvm/at.c

@@ -40,10 +40,12 @@ struct s1_walk_result {
 			u8	APTable;
 			bool	UXNTable;
 			bool	PXNTable;
+			bool	uwxn;
 			bool	uov;
 			bool	ur;
 			bool	uw;
 			bool	ux;
+			bool	pwxn;
 			bool	pov;
 			bool	pr;
 			bool	pw;
@@ -847,6 +849,8 @@ static void compute_s1_direct_permissions(struct kvm_vcpu *vcpu,
 					  struct s1_walk_info *wi,
 					  struct s1_walk_result *wr)
 {
+	bool wxn;
+
 	/* Non-hierarchical part of AArch64.S1DirectBasePermissions() */
 	if (wi->regime != TR_EL2) {
 		switch (FIELD_GET(PTE_USER | PTE_RDONLY, wr->desc)) {
@@ -884,6 +888,17 @@ static void compute_s1_direct_permissions(struct kvm_vcpu *vcpu,
 		wr->px = !(wr->desc & PTE_UXN);
 	}
 
+	switch (wi->regime) {
+	case TR_EL2:
+	case TR_EL20:
+		wxn = (vcpu_read_sys_reg(vcpu, SCTLR_EL2) & SCTLR_ELx_WXN);
+		break;
+	case TR_EL10:
+		wxn = (__vcpu_sys_reg(vcpu, SCTLR_EL1) & SCTLR_ELx_WXN);
+		break;
+	}
+
+	wr->pwxn = wr->uwxn = wxn;
 	wr->pov = wi->poe;
 	wr->uov = wi->e0poe;
 }
@@ -935,6 +950,16 @@ static void compute_s1_hierarchical_permissions(struct kvm_vcpu *vcpu,
 		(wr)->ux = (x);		\
 	} while (0)
 
+#define set_priv_wxn(wr, v)		\
+	do {				\
+		(wr)->pwxn = (v);	\
+	} while (0)
+
+#define set_unpriv_wxn(wr, v)		\
+	do {				\
+		(wr)->uwxn = (v);	\
+	} while (0)
+
 /* Similar to AArch64.S1IndirectBasePermissions(), without GCS  */
 #define set_perms(w, wr, ip)						\
 	do {								\
@@ -989,6 +1014,10 @@ static void compute_s1_hierarchical_permissions(struct kvm_vcpu *vcpu,
 			set_ ## w ## _perms((wr), false, false, false);	\
 			break;						\
 		}							\
+									\
+		/* R_HJYGR */						\
+		set_ ## w ## _wxn((wr), ((ip) == 0b0110));		\
+									\
 	} while (0)
 
 static void compute_s1_indirect_permissions(struct kvm_vcpu *vcpu,
@@ -1090,6 +1119,22 @@ static void compute_s1_permissions(struct kvm_vcpu *vcpu,
 	if (wi->poe || wi->e0poe)
 		compute_s1_overlay_permissions(vcpu, wi, wr);
 
+	/* R_QXXPC */
+	if (wr->pwxn) {
+		if (!wr->pov && wr->pw)
+			wr->px = false;
+		if (wr->pov && wr->px)
+			wr->pw = false;
+	}
+
+	/* R_NPBXC */
+	if (wr->uwxn) {
+		if (!wr->uov && wr->uw)
+			wr->ux = false;
+		if (wr->uov && wr->ux)
+			wr->uw = false;
+	}
+
 	pan = wi->pan && (wr->ur || wr->uw ||
 			  (pan3_enabled(vcpu, wi->regime) && wr->ux));
 	wr->pw &= !pan;