Message-ID: <1ea8a38f-538c-43ed-c4dc-bc3722c03489@redhat.com>
Date:   Thu, 28 Jul 2022 15:17:59 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Jithu Joseph <jithu.joseph@...el.com>, markgross@...nel.org,
        ashok.raj@...el.com, tony.luck@...el.com, ravi.v.shankar@...el.com,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH v2] platform/x86/intel/ifs: Allow non-default names for
 IFS image

Hi,

On 7/28/22 14:59, Greg KH wrote:
> On Thu, Jul 28, 2022 at 02:52:06PM +0200, Hans de Goede wrote:
>> Hi,
>>
>> On 7/28/22 14:07, Greg KH wrote:
>>> On Thu, Jul 28, 2022 at 01:57:25PM +0200, Hans de Goede wrote:
>>>> Hi,
>>>>
>>>> On 7/10/22 18:59, Greg KH wrote:
>>>>> On Sun, Jul 10, 2022 at 09:00:11AM -0700, Jithu Joseph wrote:
>>>>>> Existing implementation limits IFS images to be loaded only from
>>>>>> a default file-name /lib/firmware/intel/ifs/ff-mm-ss.scan.
>>>>>
>>>>> That was by design, why is this suddenly not acceptable?
>>>>>
>>>>>> But there are situations where there may be multiple scan files
>>>>>> that can be run on a particular system stored in /lib/firmware/intel/ifs
>>>>>
>>>>> Again, this was by design.
>>>>>
>>>>>> E.g.
>>>>>> 1. Because test contents are larger than the memory reserved for IFS by BIOS
>>>>>
>>>>> What does the BIOS have to do with this?
>>>>>
>>>>>> 2. To provide increased test coverage
>>>>>
>>>>> Test coverage of what?
>>>>>
>>>>>> 3. Custom test files to debug certain specific issues in the field
>>>>>
>>>>> Why can't you rename the existing file?
>>>>>
>>>>>> Renaming each of these to ff-mm-ss.scan and then loading might be
>>>>>> possible in some environments. But on systems where /lib is read-only
>>>>>> this is not a practical solution.
>>>>>
>>>>> What system puts /lib/ as read-only that you want to have loading
>>>>> hardware firmware?  That kind of defeats the security implications of
>>>>> having a read-only /lib/, right?
>>>>>
>>>>>> Modify the semantics of the driver file
>>>>>> /sys/devices/virtual/misc/intel_ifs_0/reload such that,
>>>>>> it interprets the input as the filename to be loaded.
>>>>>
>>>>> So you are now going to allow any file to be read from the system, in an
>>>>> unknown filesystem namespace, by this driver?
>>>>
>>>> @Intel folks to me this is the big blocker which needs to be solved before
>>>> we can move forward with figuring out how to allow loading multiple
>>>> different sets of test patterns through IFS.
>>>>
>>>> Which in turn is required to remove the broken marking...
>>>>
>>>> How about echoing a suffix to be appended to the default filename to
>>>> the reload attribute? This suffix would then need to be sanity checked
>>>> to only contain [a-z][0-9] (we don't want '/' but it seems better to
>>>> limit this further) to avoid directory traversal attacks. 
>>>>
>>>> (and echoing an empty suffix can be used to force reloading the
>>>> default test-patterns after a linux-firmware pkg upgrade)
>>>>
>>>> This way we avoid the allowing user to load an arbitrary file issue.
>>>>
>>>> Greg, would using a suffix appended to the default filename be
>>>> acceptable to you as a solution to solving the load arbitrary
>>>> file issue?
>>>
>>> Not really, a suffix doesn't protect much at all.
>>
>> ?
>>
>> Currently the driver will always load:
>>
>> /lib/firmware/intel/ifs/%02x-%02x-%02x.scan
>>
>> with the "%02x" bits being fixed parts of the CPU model.
>>
>> My suggestion is to make it:
>>
>> /lib/firmware/intel/ifs/%02x-%02x-%02x%s.scan
> 
> Ah, sorry, I skimmed that, you are right, that would be fine.  But still
> odd to ever be needed in a real system.

Ok, good. So Intel folks this seems to be a way to move forward
with this. Please prepare a version 3 using this approach.

>>> This really feels like a "test the product in the factory" type of
>>> option that someone seems to want to do without just renaming the
>>> firmware file.  Why this is unique from all other firmware file loading
>>> in the kernel needs to really be explained here in order to even
>>> consider justifying this type of change.
>>
>> First of all I really wish some of the Intel folks would elaborate
>> more on why multiple test-pattern files are necessary. Ping
>> anyone@...el, you have all been very quiet in this thread which
>> is not helpful (not helpful at all really).
>>
>> Speculating myself as far as I understand IFS is not for factory
>> tests but for testing in the fields since big cloud vendors have
>> found that sometimes there are hard to catch CPU defects which
>> they only find out by running statistics which show that certain
>> tasks only crash when run on machine a, socket b, core c.
> 
> Who knows, Intel doesn't say so we can't really guess :(

Right, for version 3 the commit message and ABI documentation changes
really need to clarify why multiple test-pattern files may be needed
mucy better. If possible please also include 1 or 2 _clear_ examples
of cases where more then 1 test-pattern file may be used.

Regards,

Hans

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