From: Nayna <nayna@linux.vnet.ibm.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>,
Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Hao Wu <hao.wu@rubrik.com>,
peterhuewe@gmx.de, jgg@ziepe.ca, arnd@arndb.de,
gregkh@linuxfoundation.org, Hamza Attak <hamza@hpe.com>,
why2jjj.linux@gmail.com, zohar@linux.vnet.ibm.com,
linux-integrity@vger.kernel.org,
Paul Menzel <pmenzel@molgen.mpg.de>,
Ken Goldman <kgold@linux.ibm.com>,
Seungyeop Han <seungyeop.han@rubrik.com>,
Shrihari Kalkar <shrihari.kalkar@rubrik.com>,
Anish Jhaveri <anish.jhaveri@rubrik.com>
Subject: Re: [PATCH] Fix Atmel TPM crash caused by too frequent queries
Date: Thu, 1 Oct 2020 14:15:13 -0400 [thread overview]
Message-ID: <19de5527-2d56-6a07-3ce7-ba216b208090@linux.vnet.ibm.com> (raw)
In-Reply-To: <1aed1b0734435959d5e53b8a4b3c18558243e6b8.camel@HansenPartnership.com>
On 10/1/20 12:53 AM, James Bottomley wrote:
> On Thu, 2020-10-01 at 04:50 +0300, Jarkko Sakkinen wrote:
>> On Wed, Sep 30, 2020 at 03:31:20PM -0700, James Bottomley wrote:
>>> On Thu, 2020-10-01 at 00:09 +0300, Jarkko Sakkinen wrote:
>>>> On Wed, Sep 30, 2020 at 01:48:15PM -0700, James Bottomley wrote:
>>>>> On Wed, 2020-09-30 at 18:37 +0300, Jarkko Sakkinen wrote:
>>>>>> On Wed, Sep 30, 2020 at 07:54:58AM -0700, James Bottomley
>>>>>> wrote:
>>>>>>> On Wed, 2020-09-30 at 05:16 +0300, Jarkko Sakkinen wrote:
>>>>>>>> On Mon, Sep 28, 2020 at 03:11:39PM -0700, James Bottomley
>>>>>>>> wrote:
>>>>>>>>> On Sun, 2020-09-27 at 22:59 -0700, Hao Wu wrote:
>>>>>>>>> [...]
>>>>>>>>>>> However, there is another possibility: it's
>>>>>>>>>>> something to do with the byte read; I notice you
>>>>>>>>>>> don't require the same slowdown for the burst count
>>>>>>>>>>> read, which actually reads the status register and
>>>>>>>>>>> burst count as a read32. If that really is the
>>>>>>>>>>> case, for the atmel would substituting a read32 and
>>>>>>>>>>> just throwing the upper bytes away in
>>>>>>>>>>> tpm_tis_status() allow us to keep the current
>>>>>>>>>>> timings? I can actually try doing this and see if
>>>>>>>>>>> it fixes my nuvoton.
>>>>>>>>>> If would be helpful if you can find the solution
>>>>>>>>>> without reducing performance. I think it is a
>>>>>>>>>> separate problem to address though. Maybe not worth
>>>>>>>>>> to mix them in the same fix.
>>>>>>>>> Well, if it works, no other fix is needed.
>>>>>>>>>
>>>>>>>>> This is what I'm currently trying out on my nuvoton
>>>>>>>>> with the timings reverted to being those in the vanilla
>>>>>>>>> kernel. So far it hasn't crashed, but I haven't run it
>>>>>>>>> for long enough to be sure yet.
>>>>>>>>>
>>>>>>>>> James
>>>>>>>> OK, so the bus does not like one byte reads but prefers
>>>>>>>> full (32-bit) word reads? I.e. what's the context?
>>>>>>> It's not supported by anything in the spec just empirical
>>>>>>> observation. However, the spec says the status register is
>>>>>>> 24 bits: the upper 16 being the burst count. When we read
>>>>>>> the whole status register, including the burst count, we do
>>>>>>> a read32. I observed that the elongated timing was only
>>>>>>> added for the read8 code not the read32 which supports the
>>>>>>> theory that the former causes the Atmel to crash but the
>>>>>>> latter doesn't. Of course it's always possible that
>>>>>>> probabilistically the Atmel is going to crash on the burst
>>>>>>> count read, but that's exercised far less than the status
>>>>>>> only read.
>>>>>> This paragraph is good enough explanation for me. Can you
>>>>>> include it to the final commit as soon as we hear how your
>>>>>> fix works for Hao?
>>>>> Sure. I'm afraid I have to report that it didn't work for
>>>>> me. My Nuvoton is definitely annoyed by the frequency of the
>>>>> prodding rather than the register width.
>>>> Sorry, this might have been stated at some point but what type of
>>>> bus is it connected with?
>>> It's hard to tell: this is my Dell Laptop, but I'd have to bet LPC.
>>>
>>>> Does it help in any way to tune the frequency?
>>> specific memory mapped address and all the conversion to the LPC
>>> back end is done by memory read/write operations. The TPM itself
>>> has a clock but doesn't give the TIS interface software control.
>> Some TPM's use tpm_tis_spi instead of MMIO.
> Yes, but I'm fairly certain mine's not SPI.
>
>>>> I also wonder if we could adjust the frequency dynamically. I.e.
>>>> start with optimistic value and lower it until finding the sweet
>>>> spot.
>>> The problem is the way this crashes: the TPM seems to be
>>> unrecoverable. If it were recoverable without a hard reset of the
>>> entire machine, we could certainly play around with it. I can try
>>> alternative mechanisms to see if anything's viable, but to all
>>> intents and purposes, it looks like my TPM simply stops responding
>>> to the TIS interface.
>> A quickly scraped idea probably with some holes in it but I was
>> thinking something like
>>
>> 1. Initially set slow value for latency, this could be the original
>> 15 ms.
>> 2. Use this to read TPM_PT_VENDOR_STRING_*.
>> 3. Lookup based vendor string from a fixup table a latency that works
>> (the fallback latency could be the existing latency).
> Well, yes, that was sort of what I was thinking of doing for the Atmel
> ... except I was thinking of using the TIS VID (16 byte assigned vendor
> ID) which means we can get the information to set the timeout before we
> have to do any TPM operations.
I wonder if the timeout issue exists for all TPM commands for the same
manufacturer. For example, does the ATMEL TPM also crash when
extending PCRs ?
In addition to defining a per TPM vendor based lookup table for timeout,
would it be a good idea to also define a Kconfig/boot param option to
allow timeout setting. This will enable to set the timeout based on the
specific use.
I was also thinking how will we decide the lookup table values for each
vendor ?
Thanks & Regards,
- Nayna
next prev parent reply other threads:[~2020-10-01 18:15 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-26 22:31 [PATCH] Fix Atmel TPM crash caused by too frequent queries Hao Wu
2020-09-26 22:57 ` James Bottomley
2020-09-26 23:10 ` Hao Wu
2020-09-27 18:25 ` James Bottomley
2020-09-28 0:11 ` Hao Wu
2020-09-28 0:15 ` Hao Wu
2020-09-28 1:22 ` James Bottomley
2020-09-28 5:59 ` Hao Wu
2020-09-28 22:11 ` James Bottomley
2020-09-29 4:46 ` Hao Wu
2020-09-30 2:16 ` Jarkko Sakkinen
2020-09-30 14:54 ` James Bottomley
2020-09-30 15:37 ` Jarkko Sakkinen
2020-09-30 20:48 ` James Bottomley
2020-09-30 21:09 ` Jarkko Sakkinen
2020-09-30 22:31 ` James Bottomley
2020-10-01 1:50 ` Jarkko Sakkinen
2020-10-01 4:53 ` James Bottomley
2020-10-01 18:15 ` Nayna [this message]
2020-10-01 18:32 ` James Bottomley
2020-10-01 23:04 ` Jarkko Sakkinen
2020-10-17 6:11 ` Hao Wu
2020-10-18 5:09 ` Jarkko Sakkinen
2020-10-18 5:20 ` Hao Wu
2020-11-14 4:39 ` Hao Wu
2020-11-18 21:11 ` Jarkko Sakkinen
2020-11-18 23:23 ` Hao Wu
2021-05-09 6:18 ` Hao Wu
2021-05-09 6:31 ` Hao Wu
2021-05-10 2:17 ` Mimi Zohar
2021-05-10 3:15 ` Hao Wu
2021-05-10 17:28 ` Jarkko Sakkinen
2020-09-28 1:08 ` Jarkko Sakkinen
2020-09-28 6:03 ` Hao Wu
2020-09-28 14:16 ` Jarkko Sakkinen
2020-09-28 17:49 ` Hao Wu
2020-09-28 19:47 ` Jarkko Sakkinen
2020-09-28 20:27 ` Hao Wu
2020-09-30 2:11 ` Jarkko Sakkinen
2020-09-30 3:41 ` Hao Wu
[not found] ` <EA1EE8F8-F054-4E1B-B830-231398D33CB8@rubrik.com>
2020-10-01 14:16 ` Mimi Zohar
-- strict thread matches above, loose matches on Subject: below --
2021-06-20 23:18 Hao Wu
2021-06-23 13:35 ` Jarkko Sakkinen
2021-06-24 5:49 ` Hao Wu
2021-06-29 20:06 ` Jarkko Sakkinen
2021-06-30 4:27 ` Hao Wu
2021-06-24 5:33 ` Hao Wu
2021-06-29 20:07 ` Jarkko Sakkinen
2020-09-14 6:13 Hao Wu
2020-09-14 6:17 ` Greg KH
2020-09-15 2:52 ` Hao Wu
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