linux-kernel - Re: [PATCH v2 01/10] vhost-scsi: protect vq->log

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Message-ID: <2f2e1de4-7c24-4851-8816-c27d162fdb53@oracle.com>
Date: Wed, 26 Mar 2025 17:22:12 -0500
From: Mike Christie <michael.christie@...cle.com>
To: Dongli Zhang <dongli.zhang@...cle.com>, virtualization@...ts.linux.dev,
        kvm@...r.kernel.org, netdev@...r.kernel.org
Cc: mst@...hat.com, jasowang@...hat.com, pbonzini@...hat.com,
        stefanha@...hat.com, eperezma@...hat.com, joao.m.martins@...cle.com,
        joe.jin@...cle.com, si-wei.liu@...cle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 01/10] vhost-scsi: protect vq->log_used with vq->mutex

On 3/17/25 6:55 PM, Dongli Zhang wrote:
> The vhost-scsi completion path may access vq->log_base when vq->log_used is
> already set to false.
> 
>     vhost-thread                       QEMU-thread
> 
> vhost_scsi_complete_cmd_work()
> -> vhost_add_used()
>    -> vhost_add_used_n()
>       if (unlikely(vq->log_used))
>                                       QEMU disables vq->log_used
>                                       via VHOST_SET_VRING_ADDR.
>                                       mutex_lock(&vq->mutex);
>                                       vq->log_used = false now!
>                                       mutex_unlock(&vq->mutex);
> 
> 				      QEMU gfree(vq->log_base)
>         log_used()
>         -> log_write(vq->log_base)
> 
> Assuming the VMM is QEMU. The vq->log_base is from QEMU userpace and can be
> reclaimed via gfree(). As a result, this causes invalid memory writes to
> QEMU userspace.
> 
> The control queue path has the same issue.
> 
> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
> ---
Reviewed-by: Mike Christie <michael.christie@...cle.com>