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svsm: Add header with SVSM_VTPM_CMD helpers

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Add helpers for the SVSM_VTPM_CMD calls used by the vTPM protocol defined by
the AMD SVSM spec [1].

The vTPM protocol follows the Official TPM 2.0 Reference Implementation
(originally by Microsoft, now part of the TCG) simulator protocol.

  [1] "Secure VM Service Module for SEV-SNP Guests"
      Publication # 58019 Revision: 1.00

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>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lore.kernel.org/r/20250403100943.120738-3-sgarzare@redhat.com
This commit is contained in:
Stefano Garzarella
2025-04-10 16:20:06 +02:00
committed by Borislav Petkov (AMD)
parent 770de678bc
commit b2849b0723
1 changed files with 149 additions and 0 deletions
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include/linux/tpm_svsm.h
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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Copyright (C) 2023 James.Bottomley@HansenPartnership.com
* Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
*
* Helpers for the SVSM_VTPM_CMD calls used by the vTPM protocol defined by the
* AMD SVSM spec [1].
*
* The vTPM protocol follows the Official TPM 2.0 Reference Implementation
* (originally by Microsoft, now part of the TCG) simulator protocol.
*
* [1] "Secure VM Service Module for SEV-SNP Guests"
* Publication # 58019 Revision: 1.00
*/
#ifndef _TPM_SVSM_H_
#define _TPM_SVSM_H_
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#define SVSM_VTPM_MAX_BUFFER 4096 /* max req/resp buffer size */
/**
* struct svsm_vtpm_request - Generic request for single word command
* @cmd: The command to send
*
* Defined by AMD SVSM spec [1] in section "8.2 SVSM_VTPM_CMD Call" -
* Table 15: vTPM Common Request/Response Structure
* Byte Size     In/Out    Description
* Offset    (Bytes)
* 0x000     4          In        Platform command
 *                         Out       Platform command response size
*/
struct svsm_vtpm_request {
u32 cmd;
};
/**
* struct svsm_vtpm_response - Generic response
* @size: The response size (zero if nothing follows)
*
* Defined by AMD SVSM spec [1] in section "8.2 SVSM_VTPM_CMD Call" -
* Table 15: vTPM Common Request/Response Structure
* Byte Size     In/Out    Description
* Offset    (Bytes)
* 0x000     4          In        Platform command
 *                         Out       Platform command response size
*
* Note: most TCG Simulator commands simply return zero here with no indication
* of success or failure.
*/
struct svsm_vtpm_response {
u32 size;
};
/**
* struct svsm_vtpm_cmd_request - Structure for a TPM_SEND_COMMAND request
* @cmd: The command to send (must be TPM_SEND_COMMAND)
* @locality: The locality
* @buf_size: The size of the input buffer following
* @buf: A buffer of size buf_size
*
* Defined by AMD SVSM spec [1] in section "8.2 SVSM_VTPM_CMD Call" -
* Table 16: TPM_SEND_COMMAND Request Structure
* Byte Size Meaning
* Offset    (Bytes)
* 0x000     4          Platform command (8)
* 0x004     1          Locality (must-be-0)
* 0x005     4          TPM Command size (in bytes)
* 0x009     Variable   TPM Command
*
* Note: the TCG Simulator expects @buf_size to be equal to the size of the
* specific TPM command, otherwise an TPM_RC_COMMAND_SIZE error is returned.
*/
struct svsm_vtpm_cmd_request {
u32 cmd;
u8 locality;
u32 buf_size;
u8 buf[];
} __packed;
/**
* struct svsm_vtpm_cmd_response - Structure for a TPM_SEND_COMMAND response
* @buf_size: The size of the output buffer following
* @buf: A buffer of size buf_size
*
* Defined by AMD SVSM spec [1] in section "8.2 SVSM_VTPM_CMD Call" -
* Table 17: TPM_SEND_COMMAND Response Structure
* Byte Size Meaning
* Offset    (Bytes)
* 0x000     4          Response size (in bytes)
* 0x004     Variable   Response
*/
struct svsm_vtpm_cmd_response {
u32 buf_size;
u8 buf[];
};
/**
* svsm_vtpm_cmd_request_fill() - Fill a TPM_SEND_COMMAND request to be sent to SVSM
* @req: The struct svsm_vtpm_cmd_request 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
svsm_vtpm_cmd_request_fill(struct svsm_vtpm_cmd_request *req, u8 locality,
const u8 *buf, size_t len)
{
if (len > SVSM_VTPM_MAX_BUFFER - sizeof(*req))
return -EINVAL;
req->cmd = 8; /* TPM_SEND_COMMAND */
req->locality = locality;
req->buf_size = len;
memcpy(req->buf, buf, len);
return 0;
}
/**
* svsm_vtpm_cmd_response_parse() - Parse a TPM_SEND_COMMAND response received from SVSM
* @resp: The struct svsm_vtpm_cmd_response 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
svsm_vtpm_cmd_response_parse(const struct svsm_vtpm_cmd_response *resp, u8 *buf,
size_t len)
{
if (len < resp->buf_size)
return -E2BIG;
if (resp->buf_size > SVSM_VTPM_MAX_BUFFER - sizeof(*resp))
return -EINVAL; // Invalid response from the platform TPM
memcpy(buf, resp->buf, resp->buf_size);
return resp->buf_size;
}
#endif /* _TPM_SVSM_H_ */