[PATCH] KVM: riscv: Fix Spectre-v1 in vector register access

[Zongmin Zhou <min_halo@163.com>]

From: Zongmin Zhou <zhouzongmin@kylinos.cn>

User-controlled register indices from the ONE_REG ioctl are used to
index into the vector register buffer (v0..v31). Sanitize the calculated
offset with array_index_nospec() to prevent speculative out-of-bounds
access.

Signed-off-by: Zongmin Zhou <zhouzongmin@kylinos.cn>
---
 arch/riscv/kvm/vcpu_vector.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kvm/vcpu_vector.c b/arch/riscv/kvm/vcpu_vector.c
index 62d2fb77bb9b..3708616e2c32 100644
--- a/arch/riscv/kvm/vcpu_vector.c
+++ b/arch/riscv/kvm/vcpu_vector.c
@@ -10,6 +10,7 @@
 #include <linux/errno.h>
 #include <linux/err.h>
 #include <linux/kvm_host.h>
+#include <linux/nospec.h>
 #include <linux/uaccess.h>
 #include <asm/cpufeature.h>
 #include <asm/kvm_isa.h>
@@ -129,11 +130,20 @@ static int kvm_riscv_vcpu_vreg_addr(struct kvm_vcpu *vcpu,
 			return -ENOENT;
 		}
 	} else if (reg_num <= KVM_REG_RISCV_VECTOR_REG(31)) {
+		unsigned long reg_offset;
+
 		if (reg_size != vlenb)
 			return -EINVAL;
 		WARN_ON(!cntx->vector.datap);
-		*reg_addr = cntx->vector.datap +
-			    (reg_num - KVM_REG_RISCV_VECTOR_REG(0)) * vlenb;
+		/*
+		 * The reg_num is derived from the userspace-provided ONE_REG
+		 * id. Sanitize it with array_index_nospec() to prevent
+		 * speculative out-of-bounds access to the vector register
+		 * buffer (32 vector registers: v0..v31).
+		 */
+		reg_offset = array_index_nospec(
+				reg_num - KVM_REG_RISCV_VECTOR_REG(0), 32);
+		*reg_addr = cntx->vector.datap + reg_offset * vlenb;
 	} else {
 		return -ENOENT;
 	}
-- 
2.34.1


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