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

[Anup Patel]

On Tue, Aug 5, 2025 at 4:24 PM Radim Krčmář <rkrcmar at ventanamicro.com> 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>

Queued this as a fix for Linux-6.17

Thanks,
Anup

> ---
>  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)
> --
> 2.50.0
>