linux-kernel - Re: [PATCH v3 05/15] habanalabs: add command buffer module

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Date:   Fri, 8 Feb 2019 21:53:27 +0200
From:   Oded Gabbay <oded.gabbay@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        Olof Johansson <olof@...om.net>,
        Mike Rapoport <rppt@...ux.ibm.com>, ogabbay@...ana.ai,
        Arnd Bergmann <arnd@...db.de>, Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v3 05/15] habanalabs: add command buffer module

On Fri, Feb 8, 2019 at 2:06 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Mon, Feb 04, 2019 at 10:32:44PM +0200, Oded Gabbay wrote:
> > +int hl_cb_ioctl(struct hl_fpriv *hpriv, void *data)
> > +{
> > +     union hl_cb_args *args = data;
> > +     struct hl_device *hdev = hpriv->hdev;
> > +     u64 handle;
> > +     int rc;
> > +
> > +     switch (args->in.op) {
> > +     case HL_CB_OP_CREATE:
> > +             rc = hl_cb_create(hdev, &hpriv->cb_mgr, args->in.cb_size,
> > +                                     &handle, hpriv->ctx->asid);
>
> so cb_size comes from userspace, ok, you check for the value to be too
> small, but not too big.  That means someone can try to allocate too much
> memory, possibly crashing things, not good :(
Yes, correct, but even if I limit a single allocation to, let's say,
1MB, what's stopping a userspace process from allocating multiple CBs
and draining the system memory ? I'm counting on the oom module to
kill that process if it mis-behaves.
And, btw, I assumed there is hard limit of 4MB on a single
dma_alloc_coherent. i.e. I was never able to allocate more then 4MB
through that API. So I never thought I need to check for max size
because of that hard limit.
Am I missing something here ?

>
>
> > +             memset(args, 0, sizeof(*args));
> > +             args->out.cb_handle = handle;
> > +             break;
> > +     case HL_CB_OP_DESTROY:
> > +             rc = hl_cb_destroy(hdev, &hpriv->cb_mgr,
> > +                                     args->in.cb_handle);
> > +             memset(args, 0, sizeof(*args));
>
> Why zero this if it's not copied back to userspace?
Fixed
>
>
>
> > +             break;
> > +     default:
> > +             rc = -EINVAL;
>
> -ENOTTY is normally the "invalid ioctl value", right?
Fixed
>
> > +             break;
> > +     }
> > +
> > +     return rc;
> > +}
>
> thanks,
>
> greg k-h