From: Robin Murphy <robin.murphy@arm.com>
To: Benjamin Gaignard <benjamin.gaignard@linaro.org>,
Mark Rutland <mark.rutland@arm.com>
Cc: devicetree@vger.kernel.org,
Alexandre Torgue <alexandre.torgue@st.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Rob Herring <robh+dt@kernel.org>,
Maxime Coquelin <mcoquelin.stm32@gmail.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Benjamin Gaignard <benjamin.gaignard@st.com>
Subject: Re: [PATCH 0/3] STM32 Extended TrustZone Protection driver
Date: Tue, 27 Feb 2018 19:46:29 +0000 [thread overview]
Message-ID: <11c3ceb2-8b8d-de59-a0be-0777a42f63a7@arm.com> (raw)
In-Reply-To: <CA+M3ks6qV_pGdE6mr3n7TiY9VhbqEkrdH6tN=8e-A=oa4UbDHw@mail.gmail.com>
On 27/02/18 19:16, Benjamin Gaignard wrote:
> 2018-02-27 18:11 GMT+01:00 Mark Rutland <mark.rutland@arm.com>:
>> On Tue, Feb 27, 2018 at 03:09:23PM +0100, Benjamin Gaignard wrote:
>>> On early boot stages STM32MP1 platform is able to dedicate some hardware blocks
>>> to a secure OS running in TrustZone.
>>> We need to avoid using those hardware blocks on non-secure context (i.e. kernel)
>>> because read/write access will all be discarded.
>>>
>>> Extended TrustZone Protection driver register itself as listener of
>>> BUS_NOTIFY_BIND_DRIVER and check, given the device address, if the hardware block
>>> could be used in a Linux context. If not it returns NOTIFY_BAD to driver core
>>> to stop driver probing.
>>
>> Huh?
>>
>> If these devices are not usable from the non-secure side, why are they
>> not removed form the DT (or marked disabled)?
>>
>> In other cases, where resources are carved out for the secure side (e.g.
>> DRAM carveouts), that's how we handle things.
>>
>
> That true you can parse and disable a device a boot time but if DT doesn't
> exactly reflect etzpc status bits we will in trouble when try to get access to
> the device.
Well, yes. If the DT doesn't correctly represent the hardware, things
will probably go wrong; that's hardly a novel concept, and it's
certainly not unique to this particular SoC.
> Changing the DT is a software protection while etzpc is an hardware protection
> so we need to check it anyway.
There are several in-tree DT and code examples where devices are marked
as disabled on certain boards/SoC variants/etc. because attempting to
access them can abort/lock up/trigger a secure watchdog reset/etc. The
only "special" thing in this particular situation is apparently that
this device even allows its secure configuration to be probed from the
non-secure side at all.
Implementing a boardfile so that you can "check" the DT makes very
little sense to me; Linux is not a firmware validation suite.
Robin.
WARNING: multiple messages have this Message-ID (diff)
From: robin.murphy@arm.com (Robin Murphy)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 0/3] STM32 Extended TrustZone Protection driver
Date: Tue, 27 Feb 2018 19:46:29 +0000 [thread overview]
Message-ID: <11c3ceb2-8b8d-de59-a0be-0777a42f63a7@arm.com> (raw)
In-Reply-To: <CA+M3ks6qV_pGdE6mr3n7TiY9VhbqEkrdH6tN=8e-A=oa4UbDHw@mail.gmail.com>
On 27/02/18 19:16, Benjamin Gaignard wrote:
> 2018-02-27 18:11 GMT+01:00 Mark Rutland <mark.rutland@arm.com>:
>> On Tue, Feb 27, 2018 at 03:09:23PM +0100, Benjamin Gaignard wrote:
>>> On early boot stages STM32MP1 platform is able to dedicate some hardware blocks
>>> to a secure OS running in TrustZone.
>>> We need to avoid using those hardware blocks on non-secure context (i.e. kernel)
>>> because read/write access will all be discarded.
>>>
>>> Extended TrustZone Protection driver register itself as listener of
>>> BUS_NOTIFY_BIND_DRIVER and check, given the device address, if the hardware block
>>> could be used in a Linux context. If not it returns NOTIFY_BAD to driver core
>>> to stop driver probing.
>>
>> Huh?
>>
>> If these devices are not usable from the non-secure side, why are they
>> not removed form the DT (or marked disabled)?
>>
>> In other cases, where resources are carved out for the secure side (e.g.
>> DRAM carveouts), that's how we handle things.
>>
>
> That true you can parse and disable a device a boot time but if DT doesn't
> exactly reflect etzpc status bits we will in trouble when try to get access to
> the device.
Well, yes. If the DT doesn't correctly represent the hardware, things
will probably go wrong; that's hardly a novel concept, and it's
certainly not unique to this particular SoC.
> Changing the DT is a software protection while etzpc is an hardware protection
> so we need to check it anyway.
There are several in-tree DT and code examples where devices are marked
as disabled on certain boards/SoC variants/etc. because attempting to
access them can abort/lock up/trigger a secure watchdog reset/etc. The
only "special" thing in this particular situation is apparently that
this device even allows its secure configuration to be probed from the
non-secure side at all.
Implementing a boardfile so that you can "check" the DT makes very
little sense to me; Linux is not a firmware validation suite.
Robin.
next prev parent reply other threads:[~2018-02-27 19:46 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-27 14:09 [PATCH 0/3] STM32 Extended TrustZone Protection driver Benjamin Gaignard
2018-02-27 14:09 ` Benjamin Gaignard
2018-02-27 14:09 ` [PATCH 1/3] driver core: check notifier_call_chain return value Benjamin Gaignard
2018-02-27 14:09 ` Benjamin Gaignard
2018-03-15 17:10 ` Greg KH
2018-03-15 17:10 ` Greg KH
2018-03-16 8:53 ` Benjamin Gaignard
2018-03-16 8:53 ` Benjamin Gaignard
2018-02-27 14:09 ` [PATCH 2/3] dt-bindings: stm32: Add bindings for Extended TrustZone Protection Benjamin Gaignard
2018-02-27 14:09 ` Benjamin Gaignard
2018-02-27 14:09 ` [PATCH 3/3] ARM: mach-stm32: Add Extended TrustZone Protection driver Benjamin Gaignard
2018-02-27 14:09 ` Benjamin Gaignard
2018-02-27 17:14 ` Mark Rutland
2018-02-27 17:14 ` Mark Rutland
2018-02-27 19:23 ` Benjamin Gaignard
2018-02-27 19:23 ` Benjamin Gaignard
2018-02-27 17:11 ` [PATCH 0/3] STM32 " Mark Rutland
2018-02-27 17:11 ` Mark Rutland
2018-02-27 19:16 ` Benjamin Gaignard
2018-02-27 19:16 ` Benjamin Gaignard
2018-02-27 19:46 ` Robin Murphy [this message]
2018-02-27 19:46 ` Robin Murphy
2018-02-28 7:53 ` Benjamin Gaignard
2018-02-28 7:53 ` Benjamin Gaignard
2018-02-28 17:53 ` Mark Rutland
2018-02-28 17:53 ` Mark Rutland
2018-02-28 18:32 ` Robin Murphy
2018-02-28 18:32 ` Robin Murphy
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