linux-kernel - Re: [PATCH v2 2/6] driver core: Add common support to skip probe for un-authorized devices

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Message-ID: <20210930204447.GA482974@rowland.harvard.edu>
Date:   Thu, 30 Sep 2021 16:44:47 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Jason Wang <jasowang@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-usb@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        "Reshetova, Elena" <elena.reshetova@...el.com>
Subject: Re: [PATCH v2 2/6] driver core: Add common support to skip probe for
 un-authorized devices

On Thu, Sep 30, 2021 at 12:23:36PM -0700, Andi Kleen wrote:
> 
> > I don't think the current mitigations under discussion here are about
> > keeping the system working. In fact most encrypted VM configs tend to
> > stop booting as a preferred way to handle security issues.
> 
> Maybe we should avoid the "trusted" term here. We're only really using it
> because USB is using it and we're now using a common framework like Greg
> requested. But I don't think it's the right way to think about it.
> 
> We usually call the drivers "hardened". The requirement for a hardened
> driver is that all interactions through MMIO/port/config space IO/MSRs are
> sanitized and do not cause memory safety issues or other information leaks.
> Other than that there is no requirement on the functionality. In particular
> DOS is ok since a malicious hypervisor can decide to not run the guest at
> any time anyways.
> 
> Someone loading an malicious driver inside the guest would be out of scope.
> If an attacker can do that inside the guest you already violated the
> security mechanisms and there are likely easier ways to take over the guest
> or leak data.
> 
> The goal of the device filter mechanism is to prevent loading unhardened
> drivers that could be exploited without them being themselves malicious.

If all you want to do is prevent someone from loading a bunch of 
drivers that you have identified as unhardened, why not just use a 
modprobe blacklist?  Am I missing something?

Alan Stern