Re: [RFC PATCH v2 4/6] tpm: add interface to interact with devices based on TCG Simulator

Jarkko Sakkinen
2025-03-01T01:48:40Z

On Fri, Feb 28, 2025 at 06:07:18PM +0100, Stefano Garzarella wrote:
> This is primarily designed to support an enlightened driver for the

The commit message is half-way cut.

I.e. it lacks the explanation of "this".

> AMD SVSM based vTPM, but it could be used by any TPM driver which
> communicates with a TPM device implemented through the TCG TPM reference
> implementation (https://github.com/TrustedComputingGroup/TPM)
>
> Co-developed-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> Co-developed-by: Claudio Carvalho <cclaudio@linux.ibm.com>
> Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> James, Claudio are you fine with the Cdb, Sob?
> The code is based to what was in the initial RFC, but I removed the
> tpm_platform module, moved some code in the header, changed some names,
> etc.
> For these reasons I reset the author but added C-o-b.
> Please, let me know if this is okay or if I need to do anything
> else (reset the author, etc.)
> ---
> include/linux/tpm_tcgsim.h | 136 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 136 insertions(+)
> create mode 100644 include/linux/tpm_tcgsim.h
>
> diff --git a/include/linux/tpm_tcgsim.h b/include/linux/tpm_tcgsim.h
> new file mode 100644
> index 000000000000..bd5b123c393b
> --- /dev/null
> +++ b/include/linux/tpm_tcgsim.h
> @@ -0,0 +1,136 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2023 James.Bottomley@HansenPartnership.com
> + * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
> + *
> + * Generic interface usable by TPM drivers interacting with devices
> + * implemented through the TCG Simulator.
> + */
> +#ifndef _TPM_TCGSIM_H_
> +#define _TPM_TCGSIM_H_
> +
> +#include <linux/errno.h>
> +#include <linux/string.h>
> +#include <linux/types.h>
> +
> +/*
> + * The current TCG Simulator TPM commands we support. The complete list is
> + * in the TcpTpmProtocol header:
> + *
> + * https://github.com/TrustedComputingGroup/TPM/blob/main/TPMCmd/Simulator/include/TpmTcpProtocol.h

We should not be dependent on any out-of-tree headers.

> + */
> +
> +#define TPM_SEND_COMMAND 8
> +#define TPM_SIGNAL_CANCEL_ON 9
> +#define TPM_SIGNAL_CANCEL_OFF 10
> +/*
> + * Any platform specific commands should be placed here and should start
> + * at 0x8000 to avoid clashes with the TCG Simulator protocol. They should
> + * follow the same self describing buffer format below.
> + */
> +
> +#define TPM_TCGSIM_MAX_BUFFER 4096 /* max req/resp buffer size */
> +
> +/**
> + * struct tpm_req - generic request header for single word command
> + *
> + * @cmd: The command to send
> + */
> +struct tpm_req {
> + u32 cmd;
> +} __packed;
> +
> +/**
> + * struct tpm_resp - generic response header
> + *
> + * @size: The response size (zero if nothing follows)
> + *
> + * Note: most TCG Simulator commands simply return zero here with no indication
> + * of success or failure.
> + */
> +struct tpm_resp {
> + u32 size;
> +} __packed;
> +
> +/**
> + * struct tpm_send_cmd_req - Structure for a TPM_SEND_COMMAND request
> + *
> + * @hdr: The request header whit the command (must be TPM_SEND_COMMAND)
> + * @locality: The locality
> + * @inbuf_size: The size of the input buffer following
> + * @inbuf: A buffer of size inbuf_size
> + *
> + * Note that TCG Simulator expects @inbuf_size to be equal to the size of the
> + * specific TPM command, otherwise an TPM_RC_COMMAND_SIZE error is
> + * returned.
> + */
> +struct tpm_send_cmd_req {
> + struct tpm_req hdr;
> + u8 locality;
> + u32 inbuf_size;
> + u8 inbuf[];
> +} __packed;
> +
> +/**
> + * struct tpm_send_cmd_req - Structure for a TPM_SEND_COMMAND response
> + *
> + * @hdr: The response header whit the following size
> + * @outbuf: A buffer of size hdr.size
> + */
> +struct tpm_send_cmd_resp {
> + struct tpm_resp hdr;
> + u8 outbuf[];
> +} __packed;
> +
> +/**
> + * tpm_tcgsim_fill_send_cmd() - fill a struct tpm_send_cmd_req to be sent to the
> + * TCG Simulator.
> + * @req: The struct tpm_send_cmd_req to fill
> + * @locality: The locality
> + * @buf: The buffer from where to copy the payload of the command
> + * @len: The size of the buffer
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +static inline int
> +tpm_tcgsim_fill_send_cmd(struct tpm_send_cmd_req *req, u8 locality,
> + const u8 *buf, size_t len)
> +{
> + if (len > TPM_TCGSIM_MAX_BUFFER - sizeof(*req))
> + return -EINVAL;
> +
> + req->hdr.cmd = TPM_SEND_COMMAND;
> + req->locality = locality;
> + req->inbuf_size = len;
> +
> + memcpy(req->inbuf, buf, len);
> +
> + return 0;
> +}
> +
> +/**
> + * tpm_tcgsim_parse_send_cmd() - Parse a struct tpm_send_cmd_resp received from
> + * the TCG Simulator
> + * @resp: The struct tpm_send_cmd_resp to parse
> + * @buf: The buffer where to copy the response
> + * @len: The size of the buffer
> + *
> + * Return: buffer size filled with the response on success, negative error
> + * code on failure.
> + */
> +static inline int
> +tpm_tcgsim_parse_send_cmd(const struct tpm_send_cmd_resp *resp, u8 *buf,
> + size_t len)
> +{
> + if (len < resp->hdr.size)
> + return -E2BIG;
> +
> + if (resp->hdr.size > TPM_TCGSIM_MAX_BUFFER - sizeof(*resp))
> + return -EINVAL; // Invalid response from the platform TPM
> +
> + memcpy(buf, resp->outbuf, resp->hdr.size);
> +
> + return resp->hdr.size;
> +}
> +
> +#endif /* _TPM_TCGSIM_H_ */
> --
> 2.48.1
>

This commit got me lost tbh.

BR, Jarkko