RISC-V: KVM: Add support for control-flow integrity FWFT features

Control-flow integrity is controlled through a WARL field in henvcfg.
Expose the feature only if the Zicfilp/Zicfiss is supported for VS-mode.
Allow the VMM to block access to the feature by disabling the ISA
extension in the guest.

Assisted-by: YuanSheng:claude-4.7-opus
Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Link: https://lore.kernel.org/r/20260713010302.303278-8-inochiama@gmail.com
Signed-off-by: Anup Patel <anup@brainfault.org>

2 files changed, 107 insertions, 0 deletions

diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index fd4c81697617..20d9959ca44f 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -248,6 +248,8 @@ struct kvm_riscv_sbi_fwft {
 	struct kvm_riscv_sbi_fwft_feature misaligned_deleg;
 	struct kvm_riscv_sbi_fwft_feature pointer_masking;
 	struct kvm_riscv_sbi_fwft_feature pte_ad_hw_updating;
+	struct kvm_riscv_sbi_fwft_feature landing_pad;
+	struct kvm_riscv_sbi_fwft_feature shadow_stack;
 };
 
 /* If you need to interpret the index values, here is the key: */
diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
index e9b0186bbdd6..245d75aaeeff 100644
--- a/arch/riscv/kvm/vcpu_sbi_fwft.c
+++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
@@ -175,6 +175,93 @@ static long kvm_sbi_fwft_get_misaligned_delegation(struct kvm_vcpu *vcpu,
 	return SBI_SUCCESS;
 }
 
+static long kvm_sbi_fwft_set_cfi(struct kvm_vcpu *vcpu,
+				 struct kvm_sbi_fwft_config *conf,
+				 bool one_reg_access, unsigned long value,
+				 u64 flag)
+{
+	struct kvm_vcpu_config *cfg = &vcpu->arch.cfg;
+
+	if (value == 0)
+		cfg->henvcfg &= ~flag;
+	else if (value == 1)
+		cfg->henvcfg |= flag;
+	else
+		return SBI_ERR_INVALID_PARAM;
+
+	if (cfg->henvcfg & (ENVCFG_LPE | ENVCFG_SSE))
+		cfg->hedeleg |= BIT(EXC_SOFTWARE_CHECK);
+	else
+		cfg->hedeleg &= ~BIT(EXC_SOFTWARE_CHECK);
+
+	if (!one_reg_access) {
+		csr_write(CSR_HEDELEG, cfg->hedeleg);
+		/*
+		 * Both Bit LPE and SSE are in the lower part, so it is safe
+		 * to only write the henvcfg
+		 */
+		csr_write(CSR_HENVCFG, vcpu->arch.cfg.henvcfg);
+	}
+
+	return SBI_SUCCESS;
+}
+
+static bool kvm_sbi_fwft_landing_pad_supported(struct kvm_vcpu *vcpu)
+{
+	return riscv_isa_extension_available(vcpu->arch.isa, ZICFILP);
+}
+
+static void kvm_sbi_fwft_reset_landing_pad(struct kvm_vcpu *vcpu)
+{
+	struct kvm_vcpu_config *cfg = &vcpu->arch.cfg;
+
+	kvm_sbi_fwft_envcfg_flag_reset(vcpu, ENVCFG_LPE);
+	if ((cfg->henvcfg & (ENVCFG_LPE | ENVCFG_SSE)) == 0)
+		cfg->hedeleg &= ~BIT(EXC_SOFTWARE_CHECK);
+}
+
+static long kvm_sbi_fwft_set_landing_pad(struct kvm_vcpu *vcpu,
+					 struct kvm_sbi_fwft_config *conf,
+					 bool one_reg_access, unsigned long value)
+{
+	return kvm_sbi_fwft_set_cfi(vcpu, conf, one_reg_access, value, ENVCFG_LPE);
+}
+
+static long kvm_sbi_fwft_get_landing_pad(struct kvm_vcpu *vcpu,
+					 struct kvm_sbi_fwft_config *conf,
+					 bool one_reg_access, unsigned long *value)
+{
+	return kvm_sbi_fwft_envcfg_flag_get(vcpu, conf, one_reg_access, value, ENVCFG_LPE);
+}
+
+static bool kvm_sbi_fwft_shadow_stack_supported(struct kvm_vcpu *vcpu)
+{
+	return riscv_isa_extension_available(vcpu->arch.isa, ZICFISS);
+}
+
+static void kvm_sbi_fwft_reset_shadow_stack(struct kvm_vcpu *vcpu)
+{
+	struct kvm_vcpu_config *cfg = &vcpu->arch.cfg;
+
+	kvm_sbi_fwft_envcfg_flag_reset(vcpu, ENVCFG_SSE);
+	if ((cfg->henvcfg & (ENVCFG_LPE | ENVCFG_SSE)) == 0)
+		cfg->hedeleg &= ~BIT(EXC_SOFTWARE_CHECK);
+}
+
+static long kvm_sbi_fwft_set_shadow_stack(struct kvm_vcpu *vcpu,
+					  struct kvm_sbi_fwft_config *conf,
+					  bool one_reg_access, unsigned long value)
+{
+	return kvm_sbi_fwft_set_cfi(vcpu, conf, one_reg_access, value, ENVCFG_SSE);
+}
+
+static long kvm_sbi_fwft_get_shadow_stack(struct kvm_vcpu *vcpu,
+					  struct kvm_sbi_fwft_config *conf,
+					  bool one_reg_access, unsigned long *value)
+{
+	return kvm_sbi_fwft_envcfg_flag_get(vcpu, conf, one_reg_access, value, ENVCFG_SSE);
+}
+
 static bool kvm_sbi_fwft_pte_ad_hw_updating_supported(struct kvm_vcpu *vcpu)
 {
 	return riscv_isa_extension_available(vcpu->arch.isa, SVADU) &&
@@ -311,6 +398,24 @@ static const struct kvm_sbi_fwft_feature features[] = {
 		.get = kvm_sbi_fwft_get_misaligned_delegation,
 	},
 	{
+		.id = SBI_FWFT_LANDING_PAD,
+		.first_reg_num = offsetof(struct kvm_riscv_sbi_fwft, landing_pad.enable) /
+				 sizeof(unsigned long),
+		.supported = kvm_sbi_fwft_landing_pad_supported,
+		.reset = kvm_sbi_fwft_reset_landing_pad,
+		.set = kvm_sbi_fwft_set_landing_pad,
+		.get = kvm_sbi_fwft_get_landing_pad,
+	},
+	{
+		.id = SBI_FWFT_SHADOW_STACK,
+		.first_reg_num = offsetof(struct kvm_riscv_sbi_fwft, shadow_stack.enable) /
+				 sizeof(unsigned long),
+		.supported = kvm_sbi_fwft_shadow_stack_supported,
+		.reset = kvm_sbi_fwft_reset_shadow_stack,
+		.set = kvm_sbi_fwft_set_shadow_stack,
+		.get = kvm_sbi_fwft_get_shadow_stack,
+	},
+	{
 		.id = SBI_FWFT_PTE_AD_HW_UPDATING,
 		.first_reg_num = offsetof(struct kvm_riscv_sbi_fwft, pte_ad_hw_updating.enable) /
 				 sizeof(unsigned long),