[PATCH] RISC-V: KVM: fix stack overrun when loading vlenb

[Nutty Liu]

On 8/5/2025 6:44 PM, Radim Krčmář wrote:
> The userspace load can put up to 2048 bits into an xlen bit stack
> buffer.  We want only xlen bits, so check the size beforehand.
>
> Fixes: 2fa290372dfe ("RISC-V: KVM: add 'vlenb' Vector CSR")
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Radim Krčmář <rkrcmar at ventanamicro.com>
> ---
Reviewed-by: Nutty Liu <liujingqi at lanxincomputing.com>

Thanks,
Nutty
>   arch/riscv/kvm/vcpu_vector.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/arch/riscv/kvm/vcpu_vector.c b/arch/riscv/kvm/vcpu_vector.c
> index a5f88cb717f3..05f3cc2d8e31 100644
> --- a/arch/riscv/kvm/vcpu_vector.c
> +++ b/arch/riscv/kvm/vcpu_vector.c
> @@ -182,6 +182,8 @@ int kvm_riscv_vcpu_set_reg_vector(struct kvm_vcpu *vcpu,
>   		struct kvm_cpu_context *cntx = &vcpu->arch.guest_context;
>   		unsigned long reg_val;
>   
> +		if (reg_size != sizeof(reg_val))
> +			return -EINVAL;
>   		if (copy_from_user(&reg_val, uaddr, reg_size))
>   			return -EFAULT;
>   		if (reg_val != cntx->vector.vlenb)