[PATCH v17 08/14] KVM: arm64: Enforce EXLOCK for SPSR and ELR

[Mark Brown]

As per I_CFFNS and the pseudocode for the SPSR_ELx and ELR_ELx registers
a GCS exception with ExType 1 is generated for attempts to write to
those registers when both GCSCR_ELx.EXLOCKEN and PSTATE.EXLOCK are set.
Ensure that this is enforced for guests if access to these registers
from the guest is handled by the hypervisor.

Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
 arch/arm64/include/asm/kvm_emulate.h |  8 +++++++
 arch/arm64/kvm/sys_regs.c            | 42 ++++++++++++++++++++++++++++++++----
 2 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index ee774c3b8dcd..bc012c86fcd6 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -81,6 +81,14 @@ int kvm_inject_nested_irq(struct kvm_vcpu *vcpu);
 int kvm_inject_nested_sea(struct kvm_vcpu *vcpu, bool iabt, u64 addr);
 int kvm_inject_nested_serror(struct kvm_vcpu *vcpu, u64 esr);
 
+static inline void kvm_inject_exlock(struct kvm_vcpu *vcpu)
+{
+	u64 esr = FIELD_PREP(ESR_ELx_EC_MASK, ESR_ELx_EC_GCS) | ESR_ELx_IL |
+		  FIELD_PREP(ESR_ELx_ExType_MASK, ESR_ELx_ExType_EXLOCK);
+
+	kvm_inject_sync(vcpu, esr);
+}
+
 static inline void kvm_inject_nested_sve_trap(struct kvm_vcpu *vcpu)
 {
 	u64 esr = FIELD_PREP(ESR_ELx_EC_MASK, ESR_ELx_EC_SVE) |
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 1a1e45d64552..3d9f4eb9d093 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2776,14 +2776,42 @@ static bool access_sp_el1(struct kvm_vcpu *vcpu,
 	return true;
 }
 
+static inline bool sysregs_exlocked(struct kvm_vcpu *vcpu)
+{
+	u64 gcscr;
+
+	if (!kvm_has_gcs(vcpu->kvm))
+		return false;
+
+	if (!(vcpu->arch.ctxt.regs.pstate & PSR_EXLOCK_BIT))
+		return false;
+
+	/*
+	 * Note that the EXLOCKEN for the running EL is checked
+	 * regardless of the register written to.
+	 */
+	if (is_hyp_ctxt(vcpu))
+		gcscr = vcpu_read_sys_reg(vcpu, GCSCR_EL2);
+	else
+		gcscr = vcpu_read_sys_reg(vcpu, GCSCR_EL1);
+
+	return gcscr & GCSCR_ELx_EXLOCKEN;
+}
+
 static bool access_elr(struct kvm_vcpu *vcpu,
 		       struct sys_reg_params *p,
 		       const struct sys_reg_desc *r)
 {
-	if (p->is_write)
+	if (p->is_write) {
+		if (sysregs_exlocked(vcpu)) {
+			kvm_inject_exlock(vcpu);
+			return false;
+		}
+
 		vcpu_write_sys_reg(vcpu, p->regval, ELR_EL1);
-	else
+	} else {
 		p->regval = vcpu_read_sys_reg(vcpu, ELR_EL1);
+	}
 
 	return true;
 }
@@ -2792,10 +2820,16 @@ static bool access_spsr(struct kvm_vcpu *vcpu,
 			struct sys_reg_params *p,
 			const struct sys_reg_desc *r)
 {
-	if (p->is_write)
+	if (p->is_write) {
+		if (sysregs_exlocked(vcpu)) {
+			kvm_inject_exlock(vcpu);
+			return false;
+		}
+
 		__vcpu_assign_sys_reg(vcpu, SPSR_EL1, p->regval);
-	else
+	} else {
 		p->regval = __vcpu_sys_reg(vcpu, SPSR_EL1);
+	}
 
 	return true;
 }

-- 
2.47.3