[PATCH v5 19/37] KVM: arm64: Split S1 permission evaluation into direct and hierarchical parts

Marc Zyngier
2024-10-23T14:53:55Z

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>
---
arch/arm64/kvm/at.c | 162 +++++++++++++++++++++++++++-----------------
1 file changed, 98 insertions(+), 64 deletions(-)

diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
index b9d0992e91972..adcfce3f67f03 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:
--
2.39.2