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

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Message-Id: <3d7df3b0-27c5-47a2-a4a1-dde168e7848e@lanxincomputing.com>
Date: Wed, 6 Aug 2025 18:05:02 +0800
From: "Nutty Liu" <liujingqi@...xincomputing.com>
To: Radim Krčmář <rkrcmar@...tanamicro.com>, 
	<kvm-riscv@...ts.infradead.org>
Cc: <kvm@...r.kernel.org>, <linux-riscv@...ts.infradead.org>, 
	<linux-kernel@...r.kernel.org>, "Anup Patel" <anup@...infault.org>, 
	"Atish Patra" <atishp@...shpatra.org>, 
	"Paul Walmsley" <paul.walmsley@...ive.com>, 
	"Palmer Dabbelt" <palmer@...belt.com>, 
	"Albert Ou" <aou@...s.berkeley.edu>, "Alexandre Ghiti" <alex@...ti.fr>, 
	"Daniel Henrique Barboza" <dbarboza@...tanamicro.com>, 
	<stable@...r.kernel.org>
Subject: Re: [PATCH] RISC-V: KVM: fix stack overrun when loading vlenb

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@...r.kernel.org>
> Signed-off-by: Radim Krčmář <rkrcmar@...tanamicro.com>
> ---
Reviewed-by: Nutty Liu <liujingqi@...xincomputing.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)