Commit 51529773 authored by Marc Zyngier's avatar Marc Zyngier Committed by Oliver Upton
Browse files

KVM: arm64: Follow specification when implementing WXN 



The R_QXXPC and R_NPBXC rules have some interesting (and pretty
sharp) corners when defining the behaviour of of WXN at S1:

- when S1 overlay is enabled, WXN applies to the overlay and
  will remove W

- when S1 overlay is disabled, WXN applies to the base permissions
  and will remove X.

Today, we lumb the two together in a way that doesn't really match
the rules, making things awkward to follow what is happening, in
particular when overlays are enabled.

Split these two rules over two distinct paths, which makes things
a lot easier to read and validate against the architecture rules.

Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250701151648.754785-3-maz@kernel.org


Signed-off-by: default avatarOliver Upton <oliver.upton@linux.dev>
parent a508d5af

arch/arm64/kvm/at.c

+14 −14
Original line number Diff line number Diff line
@@ -1063,6 +1063,10 @@ static void compute_s1_overlay_permissions(struct kvm_vcpu *vcpu, 
		if (pov_perms & ~POE_RWX)

			pov_perms = POE_NONE;



		/* R_QXXPC, S1PrivOverflow enabled */

		if (wr->pwxn && (pov_perms & POE_X))

			pov_perms &= ~POE_W;



		wr->pr &= pov_perms & POE_R;

		wr->pw &= pov_perms & POE_W;

		wr->px &= pov_perms & POE_X;
@@ -1084,6 +1088,10 @@ static void compute_s1_overlay_permissions(struct kvm_vcpu *vcpu, 
		if (uov_perms & ~POE_RWX)

			uov_perms = POE_NONE;



		/* R_NPBXC, S1UnprivOverlay enabled */

		if (wr->uwxn && (uov_perms & POE_X))

			uov_perms &= ~POE_W;



		wr->ur &= uov_perms & POE_R;

		wr->uw &= uov_perms & POE_W;

		wr->ux &= uov_perms & POE_X;
@@ -1106,21 +1114,13 @@ static void compute_s1_permissions(struct kvm_vcpu *vcpu, 


	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_QXXPC, S1PrivOverlay disabled */

	if (!wr->pov)

		wr->px &= !(wr->pwxn && wr->pw);



	/* R_NPBXC */

	if (wr->uwxn) {

		if (!wr->uov && wr->uw)

			wr->ux = false;

		if (wr->uov && wr->ux)

			wr->uw = false;

	}

	/* R_NPBXC, S1UnprivOverlay disabled */

	if (!wr->uov)

		wr->ux &= !(wr->uwxn && wr->uw);



	pan = wi->pan && (wr->ur || wr->uw ||

			  (pan3_enabled(vcpu, wi->regime) && wr->ux));