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From: Dan Williams <dan.j.williams@intel.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Andi Kleen <ak@linux.intel.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Kuppuswamy Sathyanarayanan 
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	Borislav Petkov <bp@alien8.de>, X86 ML <x86@kernel.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Andreas Noever <andreas.noever@gmail.com>,
	Michael Jamet <michael.jamet@intel.com>,
	Yehezkel Bernat <YehezkelShB@gmail.com>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Jason Wang <jasowang@redhat.com>,
	Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux PCI <linux-pci@vger.kernel.org>,
	USB list <linux-usb@vger.kernel.org>,
	virtualization@lists.linux-foundation.org, "Reshetova,
	Elena" <elena.reshetova@intel.com>
Subject: Re: [PATCH v2 2/6] driver core: Add common support to skip probe for un-authorized devices
Date: Thu, 30 Sep 2021 19:20:04 -0700	[thread overview]
Message-ID: <CAPcyv4iRo0Hd=_3jAScb5KUEJp3bU=QrWM8FYeb94SzO4gqgJA@mail.gmail.com> (raw)
In-Reply-To: <20211001014114.GB489012@rowland.harvard.edu>

On Thu, Sep 30, 2021 at 6:41 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Thu, Sep 30, 2021 at 01:52:59PM -0700, Dan Williams wrote:
> > On Thu, Sep 30, 2021 at 1:44 PM Alan Stern <stern@rowland.harvard.edu> wrote:
> > >
> > > 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?
> >
> > modules != drivers (i.e. multi-driver modules are a thing) and builtin
> > modules do not adhere to modprobe policy.
> >
> > There is also a desire to be able to support a single kernel image
> > across hosts and guests. So, if you were going to say, "just compile
> > all unnecessary drivers as modules" that defeats the common kernel
> > image goal. For confidential computing the expectation is that the
> > necessary device set is small. As you can see in the patches in this
> > case it's just a few lines of PCI ids and a hack to the virtio bus to
> > achieve the goal of disabling all extraneous devices by default.
>
>
>
> If your goal is to prevent some unwanted _drivers_ from operating --
> or all but a few desired drivers, as the case may be -- why extend
> the "authorized" API to all _devices_?  Why not instead develop a
> separate API (but of similar form) for drivers?
>
> Wouldn't that make more sense?  It corresponds a lot more directly
> with what you say you want to accomplish.

This was v1. v1 was NAKd [1] [2]:

[1]: https://lore.kernel.org/all/YQwpa+LAYt7YZ5dh@kroah.com/
[2]: https://lore.kernel.org/all/YQzDqm6FOezM6Rnu@kroah.com/

> What would you do in the theoretical case where two separate drivers
> can manage the same device, but one of them is desired (or hardened)
> and the other isn't?

Allow for user override, just like we do today for new_id, remove_id,
bind, and unbind  when default driver policy is insufficient.

echo 1 > /sys/bus/$bus/devices/$device/authorized
echo $device > /sys/bus/$bus/drivers/$desired_driver/bind

The device filter is really only necessary to bootstrap until you can
run override policy scripts. The driver firewall approach was overkill
in that regard.

WARNING: multiple messages have this Message-ID
From: Dan Williams <dan.j.williams@intel.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Kuppuswamy Sathyanarayanan
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Linux PCI <linux-pci@vger.kernel.org>,
	virtualization@lists.linux-foundation.org,
	Andreas Noever <andreas.noever@gmail.com>,
	"Reshetova, Elena" <elena.reshetova@intel.com>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Andi Kleen <ak@linux.intel.com>, Jonathan Corbet <corbet@lwn.net>,
	X86 ML <x86@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Michael Jamet <michael.jamet@intel.com>,
	Borislav Petkov <bp@alien8.de>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	USB list <linux-usb@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Yehezkel Bernat <YehezkelShB@gmail.com>
Subject: Re: [PATCH v2 2/6] driver core: Add common support to skip probe for un-authorized devices
Date: Thu, 30 Sep 2021 19:20:04 -0700	[thread overview]
Message-ID: <CAPcyv4iRo0Hd=_3jAScb5KUEJp3bU=QrWM8FYeb94SzO4gqgJA@mail.gmail.com> (raw)
In-Reply-To: <20211001014114.GB489012@rowland.harvard.edu>

On Thu, Sep 30, 2021 at 6:41 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Thu, Sep 30, 2021 at 01:52:59PM -0700, Dan Williams wrote:
> > On Thu, Sep 30, 2021 at 1:44 PM Alan Stern <stern@rowland.harvard.edu> wrote:
> > >
> > > 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?
> >
> > modules != drivers (i.e. multi-driver modules are a thing) and builtin
> > modules do not adhere to modprobe policy.
> >
> > There is also a desire to be able to support a single kernel image
> > across hosts and guests. So, if you were going to say, "just compile
> > all unnecessary drivers as modules" that defeats the common kernel
> > image goal. For confidential computing the expectation is that the
> > necessary device set is small. As you can see in the patches in this
> > case it's just a few lines of PCI ids and a hack to the virtio bus to
> > achieve the goal of disabling all extraneous devices by default.
>
>
>
> If your goal is to prevent some unwanted _drivers_ from operating --
> or all but a few desired drivers, as the case may be -- why extend
> the "authorized" API to all _devices_?  Why not instead develop a
> separate API (but of similar form) for drivers?
>
> Wouldn't that make more sense?  It corresponds a lot more directly
> with what you say you want to accomplish.

This was v1. v1 was NAKd [1] [2]:

[1]: https://lore.kernel.org/all/YQwpa+LAYt7YZ5dh@kroah.com/
[2]: https://lore.kernel.org/all/YQzDqm6FOezM6Rnu@kroah.com/

> What would you do in the theoretical case where two separate drivers
> can manage the same device, but one of them is desired (or hardened)
> and the other isn't?

Allow for user override, just like we do today for new_id, remove_id,
bind, and unbind  when default driver policy is insufficient.

echo 1 > /sys/bus/$bus/devices/$device/authorized
echo $device > /sys/bus/$bus/drivers/$desired_driver/bind

The device filter is really only necessary to bootstrap until you can
run override policy scripts. The driver firewall approach was overkill
in that regard.
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

  reply	other threads:[~2021-10-01  2:20 UTC|newest]

Thread overview: 132+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-30  1:05 [PATCH v2 0/6] Add device filter support Kuppuswamy Sathyanarayanan
2021-09-30  1:05 ` [PATCH v2 1/6] driver core: Move the "authorized" attribute from USB/Thunderbolt to core Kuppuswamy Sathyanarayanan
2021-09-30  1:42   ` Alan Stern
2021-09-30  1:42     ` Alan Stern
2021-09-30  1:55     ` Dan Williams
2021-09-30  1:55       ` Dan Williams
2021-09-30  2:38       ` Kuppuswamy, Sathyanarayanan
2021-09-30  4:59         ` Dan Williams
2021-09-30  4:59           ` Dan Williams
2021-09-30  9:05           ` Rafael J. Wysocki
2021-09-30  9:05             ` Rafael J. Wysocki
2021-09-30 14:59       ` Alan Stern
2021-09-30 14:59         ` Alan Stern
2021-09-30 15:25         ` Dan Williams
2021-09-30 15:25           ` Dan Williams
2021-09-30 11:19   ` Yehezkel Bernat
2021-09-30 15:28     ` Dan Williams
2021-09-30 15:28       ` Dan Williams
2021-09-30 18:25       ` Yehezkel Bernat
2021-09-30 19:04         ` Dan Williams
2021-09-30 19:04           ` Dan Williams
2021-09-30 19:50           ` Kuppuswamy, Sathyanarayanan
2021-09-30 20:23             ` Dan Williams
2021-09-30 20:23               ` Dan Williams
2021-09-30  1:05 ` [PATCH v2 2/6] driver core: Add common support to skip probe for un-authorized devices Kuppuswamy Sathyanarayanan
2021-09-30 10:59   ` Michael S. Tsirkin
2021-09-30 10:59     ` Michael S. Tsirkin
2021-09-30 13:52     ` Greg Kroah-Hartman
2021-09-30 13:52       ` Greg Kroah-Hartman
2021-09-30 14:38       ` Michael S. Tsirkin
2021-09-30 14:38         ` Michael S. Tsirkin
2021-09-30 14:49         ` Greg Kroah-Hartman
2021-09-30 14:49           ` Greg Kroah-Hartman
2021-09-30 15:00           ` Michael S. Tsirkin
2021-09-30 15:00             ` Michael S. Tsirkin
2021-09-30 15:22             ` Greg Kroah-Hartman
2021-09-30 15:22               ` Greg Kroah-Hartman
2021-09-30 17:17               ` Andi Kleen
2021-09-30 17:17                 ` Andi Kleen
2021-09-30 17:23                 ` Greg Kroah-Hartman
2021-09-30 17:23                   ` Greg Kroah-Hartman
2021-09-30 19:15                   ` Andi Kleen
2021-09-30 19:15                     ` Andi Kleen
2021-10-01  6:29                     ` Greg Kroah-Hartman
2021-10-01  6:29                       ` Greg Kroah-Hartman
2021-10-01 15:51                       ` Alan Stern
2021-10-01 15:51                         ` Alan Stern
2021-10-01 15:56                         ` Andi Kleen
2021-10-01 15:56                           ` Andi Kleen
2021-09-30 14:43       ` Alan Stern
2021-09-30 14:43         ` Alan Stern
2021-09-30 14:48         ` Michael S. Tsirkin
2021-09-30 14:48           ` Michael S. Tsirkin
2021-09-30 15:32           ` Alan Stern
2021-09-30 15:32             ` Alan Stern
2021-09-30 15:52             ` Michael S. Tsirkin
2021-09-30 15:52               ` Michael S. Tsirkin
2021-09-30 14:58         ` Michael S. Tsirkin
2021-09-30 14:58           ` Michael S. Tsirkin
2021-09-30 15:35           ` Alan Stern
2021-09-30 15:35             ` Alan Stern
2021-09-30 15:59             ` Michael S. Tsirkin
2021-09-30 15:59               ` Michael S. Tsirkin
2021-09-30 19:23               ` Andi Kleen
2021-09-30 19:23                 ` Andi Kleen
2021-09-30 20:44                 ` Alan Stern
2021-09-30 20:44                   ` Alan Stern
2021-09-30 20:52                   ` Dan Williams
2021-09-30 20:52                     ` Dan Williams
2021-10-01  1:41                     ` Alan Stern
2021-10-01  1:41                       ` Alan Stern
2021-10-01  2:20                       ` Dan Williams [this message]
2021-10-01  2:20                         ` Dan Williams
2021-09-30 21:12                   ` Andi Kleen
2021-09-30 21:12                     ` Andi Kleen
2021-09-30  1:05 ` [PATCH v2 3/6] driver core: Allow arch to initialize the authorized attribute Kuppuswamy Sathyanarayanan
2021-09-30  1:05 ` [PATCH v2 4/6] virtio: Initialize authorized attribute for confidential guest Kuppuswamy Sathyanarayanan
2021-09-30 11:03   ` Michael S. Tsirkin
2021-09-30 11:03     ` Michael S. Tsirkin
2021-09-30 13:36     ` Dan Williams
2021-09-30 13:36       ` Dan Williams
2021-09-30 13:49       ` Greg Kroah-Hartman
2021-09-30 13:49         ` Greg Kroah-Hartman
2021-09-30 15:18       ` Kuppuswamy, Sathyanarayanan
2021-09-30 15:20         ` Michael S. Tsirkin
2021-09-30 15:20           ` Michael S. Tsirkin
2021-09-30 15:23           ` Kuppuswamy, Sathyanarayanan
2021-09-30 15:23         ` Greg Kroah-Hartman
2021-09-30 15:23           ` Greg Kroah-Hartman
2021-09-30 19:04           ` Kuppuswamy, Sathyanarayanan
2021-09-30 19:16             ` Kuppuswamy, Sathyanarayanan
2021-09-30 19:30             ` Andi Kleen
2021-09-30 19:30               ` Andi Kleen
2021-09-30 19:40               ` Kuppuswamy, Sathyanarayanan
2021-10-01  7:03             ` Greg Kroah-Hartman
2021-10-01  7:03               ` Greg Kroah-Hartman
2021-10-01 15:49               ` Andi Kleen
2021-10-01 15:49                 ` Andi Kleen
2021-10-02 11:04                 ` Michael S. Tsirkin
2021-10-02 11:04                   ` Michael S. Tsirkin
2021-10-02 11:14                   ` Greg Kroah-Hartman
2021-10-02 11:14                     ` Greg Kroah-Hartman
2021-10-02 14:20                     ` Andi Kleen
2021-10-02 14:20                       ` Andi Kleen
2021-10-02 14:44                       ` Greg Kroah-Hartman
2021-10-02 14:44                         ` Greg Kroah-Hartman
2021-10-02 18:40                       ` Michael S. Tsirkin
2021-10-02 18:40                         ` Michael S. Tsirkin
2021-10-03  6:40                         ` Greg Kroah-Hartman
2021-10-03  6:40                           ` Greg Kroah-Hartman
2021-10-04 21:04                       ` Dan Williams
2021-10-04 21:04                         ` Dan Williams
2021-10-01 16:13               ` Dan Williams
2021-10-01 16:13                 ` Dan Williams
2021-10-01 16:45                 ` Alan Stern
2021-10-01 16:45                   ` Alan Stern
2021-10-01 18:09                   ` Dan Williams
2021-10-01 18:09                     ` Dan Williams
2021-10-01 19:00                     ` Alan Stern
2021-10-01 19:00                       ` Alan Stern
2021-10-01 19:45                       ` Kuppuswamy, Sathyanarayanan
2021-10-01 19:57                       ` Dan Williams
2021-10-01 19:57                         ` Dan Williams
2021-10-04  5:16                         ` Mika Westerberg
2021-10-05 22:33                           ` Dan Williams
2021-10-05 22:33                             ` Dan Williams
2021-10-06  5:45                             ` Greg Kroah-Hartman
2021-10-06  5:45                               ` Greg Kroah-Hartman
2021-09-30 19:25         ` Andi Kleen
2021-09-30 19:25           ` Andi Kleen
2021-09-30  1:05 ` [PATCH v2 5/6] x86/tdx: Add device filter support for x86 TDX guest platform Kuppuswamy Sathyanarayanan
2021-09-30  1:05 ` [PATCH v2 6/6] PCI: Initialize authorized attribute for confidential guest Kuppuswamy Sathyanarayanan

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