linux-kernel - [PATCH v2 3/3] KVM: arm64: Hide S1PIE registers from userspace when disabled for guests

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Message-Id: <20240822-kvm-arm64-hide-pie-regs-v2-3-376624fa829c@kernel.org>
Date: Thu, 22 Aug 2024 00:35:38 +0100
From: Mark Brown <broonie@...nel.org>
To: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
 James Morse <james.morse@....com>, 
 Suzuki K Poulose <suzuki.poulose@....com>, 
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
 Joey Gouly <joey.gouly@....com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>, 
 20240813144738.2048302-1-maz@...nel.org
Subject: [PATCH v2 3/3] KVM: arm64: Hide S1PIE registers from userspace
 when disabled for guests

When the guest does not support S1PIE we should not allow any access
to the system registers it adds in order to ensure that we do not create
spurious issues with guest migration. Add a visibility operation for these
registers.

Fixes: 86f9de9db178 ("KVM: arm64: Save/restore PIE registers")
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 arch/arm64/include/asm/kvm_host.h |  3 +++
 arch/arm64/kvm/sys_regs.c         | 35 ++++++++++++++++++++++++++++++-----
 2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 7889e5f4009f..fd161d41df52 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -1479,4 +1479,7 @@ void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val);
 #define kvm_has_tcr2(k)				\
 	(kvm_has_feat((k), ID_AA64MMFR3_EL1, TCRX, IMP))
 
+#define kvm_has_s1pie(k)				\
+	(kvm_has_feat((k), ID_AA64MMFR3_EL1, S1PIE, IMP))
+
 #endif /* __ARM64_KVM_HOST_H__ */
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 6d5f43781042..3824f6d13bf6 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2340,6 +2340,27 @@ static unsigned int tcr2_el2_visibility(const struct kvm_vcpu *vcpu,
 	return tcr2_visibility(vcpu, rd);
 }
 
+static unsigned int s1pie_visibility(const struct kvm_vcpu *vcpu,
+				     const struct sys_reg_desc *rd)
+{
+	if (kvm_has_s1pie(vcpu->kvm))
+		return 0;
+
+	return REG_HIDDEN;
+}
+
+static unsigned int s1pie_el2_visibility(const struct kvm_vcpu *vcpu,
+					 const struct sys_reg_desc *rd)
+{
+	unsigned int r;
+
+	r = el2_visibility(vcpu, rd);
+	if (r)
+		return r;
+
+	return s1pie_visibility(vcpu, rd);
+}
+
 /*
  * Architected system registers.
  * Important: Must be sorted ascending by Op0, Op1, CRn, CRm, Op2
@@ -2577,8 +2598,10 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ SYS_DESC(SYS_PMMIR_EL1), trap_raz_wi },
 
 	{ SYS_DESC(SYS_MAIR_EL1), access_vm_reg, reset_unknown, MAIR_EL1 },
-	{ SYS_DESC(SYS_PIRE0_EL1), NULL, reset_unknown, PIRE0_EL1 },
-	{ SYS_DESC(SYS_PIR_EL1), NULL, reset_unknown, PIR_EL1 },
+	{ SYS_DESC(SYS_PIRE0_EL1), NULL, reset_unknown, PIRE0_EL1,
+	  .visibility = s1pie_visibility },
+	{ SYS_DESC(SYS_PIR_EL1), NULL, reset_unknown, PIR_EL1,
+	  .visibility = s1pie_visibility },
 	{ SYS_DESC(SYS_AMAIR_EL1), access_vm_reg, reset_amair_el1, AMAIR_EL1 },
 
 	{ SYS_DESC(SYS_LORSA_EL1), trap_loregion },
@@ -2875,8 +2898,10 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	EL2_REG(HPFAR_EL2, access_rw, reset_val, 0),
 
 	EL2_REG(MAIR_EL2, access_rw, reset_val, 0),
-	EL2_REG(PIRE0_EL2, check_s1pie_access_rw, reset_val, 0),
-	EL2_REG(PIR_EL2, check_s1pie_access_rw, reset_val, 0),
+	EL2_REG_FILTERED(PIRE0_EL2, check_s1pie_access_rw, reset_val, 0,
+			 s1pie_el2_visibility),
+	EL2_REG_FILTERED(PIR_EL2, check_s1pie_access_rw, reset_val, 0,
+			 s1pie_el2_visibility),
 	EL2_REG(AMAIR_EL2, access_rw, reset_val, 0),
 
 	EL2_REG(VBAR_EL2, access_rw, reset_val, 0),
@@ -4691,7 +4716,7 @@ void kvm_calculate_traps(struct kvm_vcpu *vcpu)
 						HFGITR_EL2_TLBIRVAAE1OS	|
 						HFGITR_EL2_TLBIRVAE1OS);
 
-	if (!kvm_has_feat(kvm, ID_AA64MMFR3_EL1, S1PIE, IMP))
+	if (!kvm_has_s1pie(kvm))
 		kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nPIRE0_EL1 |
 						HFGxTR_EL2_nPIR_EL1);
 

-- 
2.39.2