KVM: riscv: Fix Spectre-v1 in ONE_REG register access

User-controlled register indices from the ONE_REG ioctl are used to
index into arrays of register values. Sanitize them with
array_index_nospec() to prevent speculative out-of-bounds access.

Reviewed-by: Radim Krčmář <radim.krcmar@oss.qualcomm.com>
Signed-off-by: Lukas Gerlach <lukas.gerlach@cispa.de>
Link: https://lore.kernel.org/r/20260303-kvm-riscv-spectre-v1-v2-1-192caab8e0dc@cispa.de
Signed-off-by: Anup Patel <anup@brainfault.org>

Author: Lukas Gerlach

arch/riscv/kvm/vcpu_onereg.c

@@ -10,6 +10,7 @@
 #include <linux/bitops.h>
 #include <linux/errno.h>
 #include <linux/err.h>
+#include <linux/nospec.h>
 #include <linux/uaccess.h>
 #include <linux/kvm_host.h>
 #include <asm/cacheflush.h>
@@ -127,6 +128,7 @@ static int kvm_riscv_vcpu_isa_check_host(unsigned long kvm_ext, unsigned long *g
 	    kvm_ext >= ARRAY_SIZE(kvm_isa_ext_arr))
 		return -ENOENT;
 
+	kvm_ext = array_index_nospec(kvm_ext, ARRAY_SIZE(kvm_isa_ext_arr));
 	*guest_ext = kvm_isa_ext_arr[kvm_ext];
 	switch (*guest_ext) {
 	case RISCV_ISA_EXT_SMNPM:
@@ -443,13 +445,16 @@ static int kvm_riscv_vcpu_get_reg_core(struct kvm_vcpu *vcpu,
 	unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
 					    KVM_REG_SIZE_MASK |
 					    KVM_REG_RISCV_CORE);
+	unsigned long regs_max = sizeof(struct kvm_riscv_core) / sizeof(unsigned long);
 	unsigned long reg_val;
 
 	if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
 		return -EINVAL;
-	if (reg_num >= sizeof(struct kvm_riscv_core) / sizeof(unsigned long))
+	if (reg_num >= regs_max)
 		return -ENOENT;
 
+	reg_num = array_index_nospec(reg_num, regs_max);
+
 	if (reg_num == KVM_REG_RISCV_CORE_REG(regs.pc))
 		reg_val = cntx->sepc;
 	else if (KVM_REG_RISCV_CORE_REG(regs.pc) < reg_num &&
@@ -476,13 +481,16 @@ static int kvm_riscv_vcpu_set_reg_core(struct kvm_vcpu *vcpu,
 	unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
 					    KVM_REG_SIZE_MASK |
 					    KVM_REG_RISCV_CORE);
+	unsigned long regs_max = sizeof(struct kvm_riscv_core) / sizeof(unsigned long);
 	unsigned long reg_val;
 
 	if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
 		return -EINVAL;
-	if (reg_num >= sizeof(struct kvm_riscv_core) / sizeof(unsigned long))
+	if (reg_num >= regs_max)
 		return -ENOENT;
 
+	reg_num = array_index_nospec(reg_num, regs_max);
+
 	if (copy_from_user(&reg_val, uaddr, KVM_REG_SIZE(reg->id)))
 		return -EFAULT;
 
@@ -507,10 +515,13 @@ static int kvm_riscv_vcpu_general_get_csr(struct kvm_vcpu *vcpu,
 					  unsigned long *out_val)
 {
 	struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
+	unsigned long regs_max = sizeof(struct kvm_riscv_csr) / sizeof(unsigned long);
 
-	if (reg_num >= sizeof(struct kvm_riscv_csr) / sizeof(unsigned long))
+	if (reg_num >= regs_max)
 		return -ENOENT;
 
+	reg_num = array_index_nospec(reg_num, regs_max);
+
 	if (reg_num == KVM_REG_RISCV_CSR_REG(sip)) {
 		kvm_riscv_vcpu_flush_interrupts(vcpu);
 		*out_val = (csr->hvip >> VSIP_TO_HVIP_SHIFT) & VSIP_VALID_MASK;
@@ -526,10 +537,13 @@ static int kvm_riscv_vcpu_general_set_csr(struct kvm_vcpu *vcpu,
 					  unsigned long reg_val)
 {
 	struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
+	unsigned long regs_max = sizeof(struct kvm_riscv_csr) / sizeof(unsigned long);
 
-	if (reg_num >= sizeof(struct kvm_riscv_csr) / sizeof(unsigned long))
+	if (reg_num >= regs_max)
 		return -ENOENT;
 
+	reg_num = array_index_nospec(reg_num, regs_max);
+
 	if (reg_num == KVM_REG_RISCV_CSR_REG(sip)) {
 		reg_val &= VSIP_VALID_MASK;
 		reg_val <<= VSIP_TO_HVIP_SHIFT;
@@ -548,11 +562,14 @@ static inline int kvm_riscv_vcpu_smstateen_set_csr(struct kvm_vcpu *vcpu,
 						   unsigned long reg_val)
 {
 	struct kvm_vcpu_smstateen_csr *csr = &vcpu->arch.smstateen_csr;
+	unsigned long regs_max = sizeof(struct kvm_riscv_smstateen_csr) /
+		sizeof(unsigned long);
 
-	if (reg_num >= sizeof(struct kvm_riscv_smstateen_csr) /
-		sizeof(unsigned long))
+	if (reg_num >= regs_max)
 		return -EINVAL;
 
+	reg_num = array_index_nospec(reg_num, regs_max);
+
 	((unsigned long *)csr)[reg_num] = reg_val;
 	return 0;
 }
@@ -562,11 +579,14 @@ static int kvm_riscv_vcpu_smstateen_get_csr(struct kvm_vcpu *vcpu,
 					    unsigned long *out_val)
 {
 	struct kvm_vcpu_smstateen_csr *csr = &vcpu->arch.smstateen_csr;
+	unsigned long regs_max = sizeof(struct kvm_riscv_smstateen_csr) /
+		sizeof(unsigned long);
 
-	if (reg_num >= sizeof(struct kvm_riscv_smstateen_csr) /
-		sizeof(unsigned long))
+	if (reg_num >= regs_max)
 		return -EINVAL;
 
+	reg_num = array_index_nospec(reg_num, regs_max);
+
 	*out_val = ((unsigned long *)csr)[reg_num];
 	return 0;
 }