linux-kernel - Re: [RFC PATCH] tpm, tpm_vtpm

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Message-ID: <bfcc3a24-b48c-48a6-8280-07f7a2669e6b@infradead.org>
Date: Wed, 16 Jul 2025 11:44:02 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Jarkko Sakkinen <jarkko@...nel.org>, linux-kernel@...r.kernel.org
Cc: keyrings@...r.kernel.org, linux-integrity@...r.kernel.org,
 Stefan Berger <stefanb@...ux.ibm.com>,
 Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>,
 Jonathan Corbet <corbet@....net>, Peter Huewe <peterhuewe@....de>,
 Jason Gunthorpe <jgg@...pe.ca>, Andrew Morton <akpm@...ux-foundation.org>,
 "Paul E. McKenney" <paulmck@...nel.org>, Steven Rostedt
 <rostedt@...dmis.org>, Neeraj Upadhyay <Neeraj.Upadhyay@....com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, Arnd Bergmann <arnd@...db.de>,
 Frank van der Linden <fvdl@...gle.com>,
 "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [RFC PATCH] tpm, tpm_vtpm_proxy: boot-time TPM

(mostly nits, along with Paul's comments)


On 7/16/25 5:18 AM, Jarkko Sakkinen wrote:
> From: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>
> 
> Provide a kernel command-line parameter named as `supplicant`, which
> contains a path to an TPM emulator binary. When defind, the kernel will

                  to a TPM

> launch the program during boot-time.
> 
> This feature is most useful in feature testing e.g., in environments

                                         testing, e.g.,

> where other means are not possible, such as CI runners. Its original use
> case highlights also quite well of its applicability for pre-production
> hardware: it was used to provide a TPM implemnentation for a RISC-V SoC
> running on FPGA with no TPM HW implementation at the time.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>
> ---
> Bumped into this in my archives so thought to make it available just in
> case anyone is interested.
> ---
>  .../admin-guide/kernel-parameters.txt         | 14 +++++
>  drivers/char/tpm/tpm_vtpm_proxy.c             | 51 +++++++++++++++++++
>  2 files changed, 65 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f1f2c0874da9..e062de99480e 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -7230,6 +7230,20 @@
>  			defined by Trusted Computing Group (TCG) see
>  			https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
>  
> +	tpm_vtpm_proxy.supplicant= [TPM]
> +			When defined, this field must contain a legit path to a

			                                        legitimate
or			                                        valid

> +			program emulating a TPM chip, which will be started
> +			during the driver initialization, thus providing a
> +			mechanism for the user space have an emulated TPM from
> +			the get go. Kernel prepares the process with a file

			    get-go.
or just don't use slang terms.

> +			pre-opened file descriptor in the index 3 for
> +			/dev/vtpmx.
> +
> +			An emulator can optionally provide support for
> +			localities by reacting to the vendor command defined
> +			by the driver: 0x20001000. Its payload is a single
> +			byte containing the new locality.
> +
>  	tp_printk	[FTRACE]
>  			Have the tracepoints sent to printk as well as the
>  			tracing ring buffer. This is useful for early boot up

thanks.
-- 
~Randy