Re: [PATCH] RISC-V: KVM: Fix invalid HVA warning in steal-time recording

[Andrew Jones]

On Wed, Apr 15, 2026 at 07:52:16AM +0000, Jiakai Xu wrote:
> kvm_riscv_vcpu_record_steal_time() assumes that the steal-time shared
> memory GPA (vcpu->arch.sta.shmem) is always backed by a valid guest
> memory slot. However, this assumption is not guaranteed by the KVM
> userspace ABI.
> 
> A malicious or buggy userspace can set the STA shared memory GPA via
> KVM_SET_ONE_REG without establishing a corresponding memory region via
> KVM_SET_USER_MEMORY_REGION. In such cases, the GPA cannot be translated
> to a valid HVA and kvm_vcpu_gfn_to_hva() returns an error address.
> 
> The current implementation incorrectly treats this as a kernel warning
> using WARN_ON(), which may escalate to a kernel panic when panic_on_warn
> is enabled.
> 
> This is not a kernel bug condition but a normal invalid configuration
> from userspace, and should be handled gracefully.
> 
> Fix it by removing WARN_ON() and treating invalid HVA as a normal
> failure case, resetting the STA shared memory state.
> 
> Fixes: e9f12b5fff8ad0 ("RISC-V: KVM: Implement SBI STA extension")
> Signed-off-by: Jiakai Xu <xujiakai2025@xxxxxxxxxxx>
> Signed-off-by: Jiakai Xu <jiakaiPeanut@xxxxxxxxx>
> Assisted-by: OpenClaw:DeepSeek-V3.2
> ---
>  arch/riscv/kvm/vcpu_sbi_sta.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/kvm/vcpu_sbi_sta.c b/arch/riscv/kvm/vcpu_sbi_sta.c
> index 3b834709b429f..60e50296a0085 100644
> --- a/arch/riscv/kvm/vcpu_sbi_sta.c
> +++ b/arch/riscv/kvm/vcpu_sbi_sta.c
> @@ -46,7 +46,7 @@ void kvm_riscv_vcpu_record_steal_time(struct kvm_vcpu *vcpu)
>  	gfn = shmem >> PAGE_SHIFT;
>  	hva = kvm_vcpu_gfn_to_hva(vcpu, gfn);
>  
> -	if (WARN_ON(kvm_is_error_hva(hva))) {
> +	if (kvm_is_error_hva(hva)) {
>  		vcpu->arch.sta.shmem = INVALID_GPA;
>  		return;
>  	}
> -- 
> 2.34.1
>

Reviewed-by: Andrew Jones <andrew.jones@xxxxxxxxxxxxxxxx>