KVM: riscv: Fix Spectre-v1 in AIA CSR access

User-controlled indices are used to access AIA CSR registers.
Sanitize them with array_index_nospec() to prevent speculative
out-of-bounds access.

Similar to x86 commit 8c86405 ("KVM: x86: Protect
ioapic_read_indirect() from Spectre-v1/L1TF attacks") and arm64
commit 41b8759 ("KVM: arm/arm64: vgic: fix possible spectre-v1
in vgic_get_irq()").

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-v2-2-192caab8e0dc@cispa.de
Signed-off-by: Anup Patel <anup@brainfault.org>

Author: Lukas Gerlach

arch/riscv/kvm/aia.c

@@ -13,6 +13,7 @@
 #include <linux/irqchip/riscv-imsic.h>
 #include <linux/irqdomain.h>
 #include <linux/kvm_host.h>
+#include <linux/nospec.h>
 #include <linux/percpu.h>
 #include <linux/spinlock.h>
 #include <asm/cpufeature.h>
@@ -182,10 +183,13 @@ int kvm_riscv_vcpu_aia_get_csr(struct kvm_vcpu *vcpu,
 			       unsigned long *out_val)
 {
 	struct kvm_vcpu_aia_csr *csr = &vcpu->arch.aia_context.guest_csr;
+	unsigned long regs_max = sizeof(struct kvm_riscv_aia_csr) / sizeof(unsigned long);
 
-	if (reg_num >= sizeof(struct kvm_riscv_aia_csr) / sizeof(unsigned long))
+	if (reg_num >= regs_max)
 		return -ENOENT;
 
+	reg_num = array_index_nospec(reg_num, regs_max);
+
 	*out_val = 0;
 	if (kvm_riscv_aia_available())
 		*out_val = ((unsigned long *)csr)[reg_num];
@@ -198,10 +202,13 @@ int kvm_riscv_vcpu_aia_set_csr(struct kvm_vcpu *vcpu,
 			       unsigned long val)
 {
 	struct kvm_vcpu_aia_csr *csr = &vcpu->arch.aia_context.guest_csr;
+	unsigned long regs_max = sizeof(struct kvm_riscv_aia_csr) / sizeof(unsigned long);
 
-	if (reg_num >= sizeof(struct kvm_riscv_aia_csr) / sizeof(unsigned long))
+	if (reg_num >= regs_max)
 		return -ENOENT;
 
+	reg_num = array_index_nospec(reg_num, regs_max);
+
 	if (kvm_riscv_aia_available()) {
 		((unsigned long *)csr)[reg_num] = val;