[PATCH v6 37/64] KVM: arm64: nv: Restrict S2 RD/WR permissions to match the guest's

Marc Zyngier
2022-01-28T13:14:11Z

When mapping a page in a shadow stage-2, special care must be
taken not to be more permissive than the guest is (writable or
readable page when the guest hasn't set that permission).

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/include/asm/kvm_nested.h | 15 +++++++++++++++
arch/arm64/kvm/mmu.c | 14 +++++++++++++-
arch/arm64/kvm/nested.c | 2 +-
3 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
index 4fad4d3848ce..f4b846d09d86 100644
--- a/arch/arm64/include/asm/kvm_nested.h
+++ b/arch/arm64/include/asm/kvm_nested.h
@@ -97,6 +97,21 @@ static inline u32 kvm_s2_trans_esr(struct kvm_s2_trans *trans)
return trans->esr;
}

+static inline bool kvm_s2_trans_readable(struct kvm_s2_trans *trans)
+{
+ return trans->readable;
+}
+
+static inline bool kvm_s2_trans_writable(struct kvm_s2_trans *trans)
+{
+ return trans->writable;
+}
+
+static inline bool kvm_s2_trans_executable(struct kvm_s2_trans *trans)
+{
+ return !(trans->upper_attr & BIT(54));
+}
+
extern int kvm_walk_nested_s2(struct kvm_vcpu *vcpu, phys_addr_t gipa,
struct kvm_s2_trans *result);

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 36f7ecb4f81b..7c56e1522d3c 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1247,6 +1247,17 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
if (exec_fault && device)
return -ENOEXEC;

+ /*
+ * Potentially reduce shadow S2 permissions to match the guest's own
+ * S2. For exec faults, we'd only reach this point if the guest
+ * actually allowed it (see kvm_s2_handle_perm_fault).
+ */
+ if (kvm_is_shadow_s2_fault(vcpu)) {
+ writable &= kvm_s2_trans_writable(nested);
+ if (!kvm_s2_trans_readable(nested))
+ prot &= ~KVM_PGTABLE_PROT_R;
+ }
+
spin_lock(&kvm->mmu_lock);
pgt = vcpu->arch.hw_mmu->pgt;
if (mmu_notifier_retry(kvm, mmu_seq))
@@ -1285,7 +1296,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,

if (device)
prot |= KVM_PGTABLE_PROT_DEVICE;
- else if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC))
+ else if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC) &&
+ kvm_s2_trans_executable(nested))
prot |= KVM_PGTABLE_PROT_X;

/*
diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 0a9708f776fc..a74ffb1d2064 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -481,7 +481,7 @@ int kvm_s2_handle_perm_fault(struct kvm_vcpu *vcpu, struct kvm_s2_trans *trans)
return 0;

if (kvm_vcpu_trap_is_iabt(vcpu)) {
- forward_fault = (trans->upper_attr & BIT(54));
+ forward_fault = !kvm_s2_trans_executable(trans);
} else {
bool write_fault = kvm_is_write_fault(vcpu);