tpm_svsm.h

  1/* SPDX-License-Identifier: GPL-2.0-only */
  2/*
  3 * Copyright (C) 2023 James.Bottomley@HansenPartnership.com
  4 * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
  5 *
  6 * Helpers for the SVSM_VTPM_CMD calls used by the vTPM protocol defined by the
  7 * AMD SVSM spec [1].
  8 *
  9 * The vTPM protocol follows the Official TPM 2.0 Reference Implementation
 10 * (originally by Microsoft, now part of the TCG) simulator protocol.
 11 *
 12 * [1] "Secure VM Service Module for SEV-SNP Guests"
 13 *     Publication # 58019 Revision: 1.00
 14 */
 15#ifndef _TPM_SVSM_H_
 16#define _TPM_SVSM_H_
 17
 18#include <linux/errno.h>
 19#include <linux/string.h>
 20#include <linux/types.h>
 21
 22#define SVSM_VTPM_MAX_BUFFER		4096 /* max req/resp buffer size */
 23
 24/**
 25 * struct svsm_vtpm_request - Generic request for single word command
 26 * @cmd:	The command to send
 27 *
 28 * Defined by AMD SVSM spec [1] in section "8.2 SVSM_VTPM_CMD Call" -
 29 * Table 15: vTPM Common Request/Response Structure
 30 *     Byte      Size       In/Out    Description
 31 *     Offset    (Bytes)
 32 *     0x000     4          In        Platform command
 33 *                          Out       Platform command response size
 34 */
 35struct svsm_vtpm_request {
 36	u32 cmd;
 37};
 38
 39/**
 40 * struct svsm_vtpm_response - Generic response
 41 * @size:	The response size (zero if nothing follows)
 42 *
 43 * Defined by AMD SVSM spec [1] in section "8.2 SVSM_VTPM_CMD Call" -
 44 * Table 15: vTPM Common Request/Response Structure
 45 *     Byte      Size       In/Out    Description
 46 *     Offset    (Bytes)
 47 *     0x000     4          In        Platform command
 48 *                          Out       Platform command response size
 49 *
 50 * Note: most TCG Simulator commands simply return zero here with no indication
 51 * of success or failure.
 52 */
 53struct svsm_vtpm_response {
 54	u32 size;
 55};
 56
 57/**
 58 * struct svsm_vtpm_cmd_request - Structure for a TPM_SEND_COMMAND request
 59 * @cmd:	The command to send (must be TPM_SEND_COMMAND)
 60 * @locality:	The locality
 61 * @buf_size:	The size of the input buffer following
 62 * @buf:	A buffer of size buf_size
 63 *
 64 * Defined by AMD SVSM spec [1] in section "8.2 SVSM_VTPM_CMD Call" -
 65 * Table 16: TPM_SEND_COMMAND Request Structure
 66 *     Byte      Size       Meaning
 67 *     Offset    (Bytes)
 68 *     0x000     4          Platform command (8)
 69 *     0x004     1          Locality (must-be-0)
 70 *     0x005     4          TPM Command size (in bytes)
 71 *     0x009     Variable   TPM Command
 72 *
 73 * Note: the TCG Simulator expects @buf_size to be equal to the size of the
 74 * specific TPM command, otherwise an TPM_RC_COMMAND_SIZE error is returned.
 75 */
 76struct svsm_vtpm_cmd_request {
 77	u32 cmd;
 78	u8 locality;
 79	u32 buf_size;
 80	u8 buf[];
 81} __packed;
 82
 83/**
 84 * struct svsm_vtpm_cmd_response - Structure for a TPM_SEND_COMMAND response
 85 * @buf_size:	The size of the output buffer following
 86 * @buf:	A buffer of size buf_size
 87 *
 88 * Defined by AMD SVSM spec [1] in section "8.2 SVSM_VTPM_CMD Call" -
 89 * Table 17: TPM_SEND_COMMAND Response Structure
 90 *     Byte      Size       Meaning
 91 *     Offset    (Bytes)
 92 *     0x000     4          Response size (in bytes)
 93 *     0x004     Variable   Response
 94 */
 95struct svsm_vtpm_cmd_response {
 96	u32 buf_size;
 97	u8 buf[];
 98};
 99
100/**
101 * svsm_vtpm_cmd_request_fill() - Fill a TPM_SEND_COMMAND request to be sent to SVSM
102 * @req: The struct svsm_vtpm_cmd_request to fill
103 * @locality: The locality
104 * @buf: The buffer from where to copy the payload of the command
105 * @len: The size of the buffer
106 *
107 * Return: 0 on success, negative error code on failure.
108 */
109static inline int
110svsm_vtpm_cmd_request_fill(struct svsm_vtpm_cmd_request *req, u8 locality,
111			   const u8 *buf, size_t len)
112{
113	if (len > SVSM_VTPM_MAX_BUFFER - sizeof(*req))
114		return -EINVAL;
115
116	req->cmd = 8; /* TPM_SEND_COMMAND */
117	req->locality = locality;
118	req->buf_size = len;
119
120	memcpy(req->buf, buf, len);
121
122	return 0;
123}
124
125/**
126 * svsm_vtpm_cmd_response_parse() - Parse a TPM_SEND_COMMAND response received from SVSM
127 * @resp: The struct svsm_vtpm_cmd_response to parse
128 * @buf: The buffer where to copy the response
129 * @len: The size of the buffer
130 *
131 * Return: buffer size filled with the response on success, negative error
132 * code on failure.
133 */
134static inline int
135svsm_vtpm_cmd_response_parse(const struct svsm_vtpm_cmd_response *resp, u8 *buf,
136			     size_t len)
137{
138	if (len < resp->buf_size)
139		return -E2BIG;
140
141	if (resp->buf_size > SVSM_VTPM_MAX_BUFFER - sizeof(*resp))
142		return -EINVAL;  // Invalid response from the platform TPM
143
144	memcpy(buf, resp->buf, resp->buf_size);
145
146	return resp->buf_size;
147}
148
149#endif /* _TPM_SVSM_H_ */