linux-kernel - Re: [PATCH] RISC-V: KVM: Validate SBI STA shmem alignment in kvm_sbi_ext_sta_set

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Message-ID: <ydibz63oh6tj66utjlemeikxg7iateqoox3bwg7r4pdvbwijoj@5zxhlhesvv2t>
Date: Fri, 30 Jan 2026 14:48:00 -0600
From: Andrew Jones <andrew.jones@....qualcomm.com>
To: Jiakai Xu <jiakaipeanut@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org,
        Alexandre Ghiti <alex@...ti.fr>, Albert Ou <aou@...s.berkeley.edu>,
        Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley <pjw@...nel.org>,
        Atish Patra <atish.patra@...ux.dev>, Anup Patel <anup@...infault.org>,
        Jiakai Xu <xujiakai2025@...as.ac.cn>
Subject: Re: [PATCH] RISC-V: KVM: Validate SBI STA shmem alignment in
 kvm_sbi_ext_sta_set_reg

On Sat, Jan 24, 2026 at 02:20:42AM +0000, Jiakai Xu wrote:
...
> diff --git a/arch/riscv/kvm/vcpu_sbi_sta.c b/arch/riscv/kvm/vcpu_sbi_sta.c
> index afa0545c3bcfc..7dfe671c42eaa 100644
> --- a/arch/riscv/kvm/vcpu_sbi_sta.c
> +++ b/arch/riscv/kvm/vcpu_sbi_sta.c
> @@ -186,23 +186,25 @@ static int kvm_sbi_ext_sta_set_reg(struct kvm_vcpu *vcpu, unsigned long reg_num,
>  		return -EINVAL;
>  	value = *(const unsigned long *)reg_val;
>  
> +	gpa_t new_shmem = vcpu->arch.sta.shmem;

Please declare new_shmem at the top of the function and there's no
need to initialize it to vcpu->arch.sta.shmem. Actually it appears you
meant to initialize it to NULL, based on the 'if (new_shmem ...)' check
below.

> +
>  	switch (reg_num) {
>  	case KVM_REG_RISCV_SBI_STA_REG(shmem_lo):
>  		if (IS_ENABLED(CONFIG_32BIT)) {
>  			gpa_t hi = upper_32_bits(vcpu->arch.sta.shmem);
>  
> -			vcpu->arch.sta.shmem = value;
> -			vcpu->arch.sta.shmem |= hi << 32;
> +			new_shmem = value;
> +			new_shmem |= hi << 32;
>  		} else {
> -			vcpu->arch.sta.shmem = value;
> +			new_shmem = value;
>  		}
>  		break;
>  	case KVM_REG_RISCV_SBI_STA_REG(shmem_hi):
>  		if (IS_ENABLED(CONFIG_32BIT)) {
>  			gpa_t lo = lower_32_bits(vcpu->arch.sta.shmem);
>  
> -			vcpu->arch.sta.shmem = ((gpa_t)value << 32);
> -			vcpu->arch.sta.shmem |= lo;
> +			new_shmem = ((gpa_t)value << 32);
> +			new_shmem |= lo;
>  		} else if (value != 0) {
>  			return -EINVAL;
>  		}
> @@ -210,7 +212,10 @@ static int kvm_sbi_ext_sta_set_reg(struct kvm_vcpu *vcpu, unsigned long reg_num,
>  	default:
>  		return -ENOENT;
>  	}

Please add a blank line here.

> +	if (new_shmem && !IS_ALIGNED(new_shmem, 64))
> +		return -EINVAL;
>  
> +	vcpu->arch.sta.shmem = new_shmem;

And another blank line here.

>  	return 0;
>  }
>  
> -- 
> 2.34.1
>

Thanks,
drew