[PATCH] KVM: arm64: Inject exception on out-of-IPA-range translation fault

[Marc Zyngier]

When taking an translation fault for an IPA that is outside of
the range defined by the hypervisor (between the HW PARange and
that exposed to the guest), we stupidly treat it as an IO and
forward the access to userspace. Of course, userspace can't do
much with it, and things end badly.

Arguably, the guest is braindead, but we should at least catch the
case and inject an exception.

Check the faulting IPA against the IPA size the VM has, and
inject an Address Size Fault at level 0 if the access fails the
check.

Reported-by: Christoffer Dall <christoffer.dall at arm.com>
Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/include/asm/kvm_emulate.h |  1 +
 arch/arm64/kvm/inject_fault.c        | 28 ++++++++++++++++++++++++++++
 arch/arm64/kvm/mmu.c                 |  7 +++++++
 3 files changed, 36 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index 7496deab025a..f71358271b71 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -40,6 +40,7 @@ void kvm_inject_undefined(struct kvm_vcpu *vcpu);
 void kvm_inject_vabt(struct kvm_vcpu *vcpu);
 void kvm_inject_dabt(struct kvm_vcpu *vcpu, unsigned long addr);
 void kvm_inject_pabt(struct kvm_vcpu *vcpu, unsigned long addr);
+void kvm_inject_size_fault(struct kvm_vcpu *vcpu);
 
 void kvm_vcpu_wfi(struct kvm_vcpu *vcpu);
 
diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
index b47df73e98d7..ba20405d2dc2 100644
--- a/arch/arm64/kvm/inject_fault.c
+++ b/arch/arm64/kvm/inject_fault.c
@@ -145,6 +145,34 @@ void kvm_inject_pabt(struct kvm_vcpu *vcpu, unsigned long addr)
 		inject_abt64(vcpu, true, addr);
 }
 
+void kvm_inject_size_fault(struct kvm_vcpu *vcpu)
+{
+	unsigned long addr, esr;
+
+	addr  = kvm_vcpu_get_fault_ipa(vcpu);
+	addr |= kvm_vcpu_get_hfar(vcpu) & GENMASK(11, 0);
+
+	if (kvm_vcpu_trap_is_iabt(vcpu))
+		kvm_inject_pabt(vcpu, addr);
+	else
+		kvm_inject_dabt(vcpu, addr);
+
+	/*
+	 * If AArch64 or LPAE, set FSC to 0 to indicate an Address
+	 * Size Fault at level 0, as if exceeding PARange.
+	 *
+	 * Non-LPAE guests will only get the external abort, as there
+	 * is no way to to describe the ASF.
+	 */
+	if (vcpu_el1_is_32bit(vcpu) &&
+	    !(vcpu_read_sys_reg(vcpu, TCR_EL1) & TTBCR_EAE))
+		return;
+
+	esr = vcpu_read_sys_reg(vcpu, ESR_EL1);
+	esr &= ~GENMASK_ULL(5, 0);
+	vcpu_write_sys_reg(vcpu, esr, ESR_EL1);
+}
+
 /**
  * kvm_inject_undefined - inject an undefined instruction into the guest
  * @vcpu: The vCPU in which to inject the exception
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 53ae2c0640bc..de6c3ae4afd5 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1337,6 +1337,13 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 	fault_ipa = kvm_vcpu_get_fault_ipa(vcpu);
 	is_iabt = kvm_vcpu_trap_is_iabt(vcpu);
 
+	/* Address Size Fault? */
+	if (fault_status == FSC_FAULT &&
+	    fault_ipa >= BIT_ULL(vcpu->arch.hw_mmu->pgt->ia_bits)) {
+		kvm_inject_size_fault(vcpu);
+		return 1;
+	}
+
 	/* Synchronous External Abort? */
 	if (kvm_vcpu_abt_issea(vcpu)) {
 		/*
-- 
2.34.1