Re: [PATCH v15 19/28] x86/tpm: Early TPM PCR extending driver

Daniel P. Smith
2025-12-19T21:27:00Z

Hey Dave!

On 12/16/25 16:53, Dave Hansen wrote:
> I'm mostly spot-checking this to see what kind of shape it's in and how
> much work and diligence has been applied in the last 8 months since v14.
>
> On 12/15/25 15:33, Ross Philipson wrote:
> ...
>> The driver could be extended for further operations if needed. This
>> TPM dirver implementation relies as much as possible on existing mainline
>
> <sigh>
>
> v15 and no spell checking. :(
>
>> --- /dev/null
>> +++ b/arch/x86/boot/compressed/early_tpm_extend.c
>> @@ -0,0 +1,601 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Copyright (c) 2010-2012 United States Government, as represented by
>> + * the Secretary of Defense. All rights reserved.
>
> IANAL, but this looks fishy.
>
> It's theoretically fine to go grab random code off the Internet and
> submit it to the kernel, given the correct license. But I do want to
> know what its story is and where it came from.

Let me provide some context as to the code origin. Ross, before joining
Oracle, and I have a long history of working with DRTM/Intel TXT within
Xen. When it was requested to go back to sending the measurements to the
TPM in the setup kernel, we needed to find a minimal code base to
provide the command buffer packing until the TPM driver could be fully
refactored. We knew that Xen's vtpm framework provided a simple macro
system to provide contextual TPM command buffer packing. We decided this
would be a lightweight choice that would be easy to cut down to only
what is needed to handle the very few TPM commands we will need to send.
And to that extent, there have been internal reviews that have reduced
the amount of that original code.

> I also seem to remember that there are special rules around the US
> federal government's inability to hold copyrights. This seems worth at
> least a mention ... somewhere.

IANAL either, but in general the safest/correct approach is to retain
any CRs placed on the code being reused, and the above is the CR on the
source from the Xen tree.

> This is helpful, for instance:
>
>> + * based off of the original tools/vtpm_manager code base which is:
>> + * Copyright (c) 2005, Intel Corp.
>> + * All rights reserved.
>
> so thanks for that one.

That's the origin of all the code reuse, we can do an review to see if
any of the code that originated from the USG code is still present.

>> + * Redistribution and use in source and binary forms, with or without
>> + * modification, are permitted provided that the following conditions
>> + * are met:
>> + *
>> + * * Redistributions of source code must retain the above copyright
>> + * notice, this list of conditions and the following disclaimer.
>> + * * Redistributions in binary form must reproduce the above
>> + * copyright notice, this list of conditions and the following
>> + * disclaimer in the documentation and/or other materials provided
>> + * with the distribution.
>> + * * Neither the name of Intel Corporation nor the names of its
>> + * contributors may be used to endorse or promote products derived
>> + * from this software without specific prior written permission.
>> + *
>> + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
>> + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
>> + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
>> + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
>> + * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
>> + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
>> + * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
>> + * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
>> + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
>> + * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>> + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
>> + * OF THE POSSIBILITY OF SUCH DAMAGE.
>> + */
>
> Also, IANAL, but this looks BSD-ish.
>
> I would have kinda expected the SPDX header to say BSD-blah-blah and not
> GPL-2.0-only.
>
> I'd really appreciate if you could go have a huddle with your corporate
> Open Source folks and make sure this is all proper. To me, it looks
> fishy at _best_.
>
> ...
>> +/*
>> + * We're far too early to calibrate time. Assume a 5GHz processor (the upper
>> + * end of the Fam19h range), which causes us to be wrong in the safe direction
>> + * on slower systems.
>> + */
>
> https://docs.kernel.org/process/maintainer-tip.html#changelog
>
> Imperative voice please.
>
> ...
>> +static int __tis_recv_data(struct tpm_chip *chip, u8 *buf, int count)
>> +{
>> + int size = 0;
>> + int burstcnt;
>> +
>> + while (size < count && __tis_wait_for_stat(chip, TPM_STS_DATA_AVAIL | TPM_STS_VALID, chip->timeout_c) == 0) {
>> + burstcnt = __tis_get_burstcount(chip);
>> +
>> + for ( ; burstcnt > 0 && size < count; --burstcnt)
>> + buf[size++] = tpm_read8(chip, TPM_DATA_FIFO(chip->locality));
>> + }
>> +
>> + return size;
>> +}
>> +
>> +/**
>> + * tpm_tis_check_locality - Check if the given locality is the active one
>> + * @chip: The TPM chip instance
>> + * @loc: The locality to check
>> + *
>> + * Return: true - locality active, false - not active
>> + */
>> +bool tpm_tis_check_locality(struct tpm_chip *chip, int loc)
>> +{
>> + if ((tpm_read8(chip, TPM_ACCESS(loc)) & (TPM_ACCESS_ACTIVE_LOCALITY | TPM_ACCESS_VALID)) == (TPM_ACCESS_ACTIVE_LOCALITY | TPM_ACCESS_VALID)) {
>> + chip->locality = loc;
>> + return true;
>> + }
>> +
>> + return false;
>> +}
>> +
>> +/**
>> + * tpm_tis_release_locality - Release the active locality
>> + * @chip: The TPM chip instance
>> + */
>> +void tpm_tis_release_locality(struct tpm_chip *chip)
>> +{
>> + if ((tpm_read8(chip, TPM_ACCESS(chip->locality)) & (TPM_ACCESS_REQUEST_PENDING | TPM_ACCESS_VALID)) == (TPM_ACCESS_REQUEST_PENDING | TPM_ACCESS_VALID))
>> + tpm_write8(chip, TPM_ACCESS(chip->locality), TPM_ACCESS_RELINQUISH_LOCALITY);
>> +
>> + chip->locality = 0;
>> +}
>
> I guess some folks aren't enforcing the 80-column limits. But this is
> not even close. It's almost 80x2.
>
> Has there even been an attempt to make this conform to kernel coding
> style? What other checkpatch.pl warnings are being ignored?