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

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Message-ID: <953d2f4c-d82f-4e8f-a905-b7dfbf690ef7@ventanamicro.com>
Date: Wed, 6 Aug 2025 06:59:06 -0300
From: Daniel Henrique Barboza <dbarboza@...tanamicro.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>,
 stable@...r.kernel.org
Subject: Re: [PATCH] RISC-V: KVM: fix stack overrun when loading vlenb



On 8/5/25 7:44 AM, 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: Daniel Henrique Barboza <dbarboza@...tanamicro.com>

>   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)