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.bottom...@hansenpartnership.com>
Signed-off-by: James Bottomley <james.bottom...@hansenpartnership.com>
Co-developed-by: Claudio Carvalho <cclau...@linux.ibm.com>
Signed-off-by: Claudio Carvalho <cclau...@linux.ibm.com>
Signed-off-by: Stefano Garzarella <sgarz...@redhat.com>
---
v3:
- renamed header and prefix to make clear it's related to the SVSM vTPM
protocol
- renamed fill/parse functions [Tom]
- removed link to the spec because those URLs are unstable [Borislav]
---
include/linux/svsm_vtpm.h | 141 ++++++++++++++++++++++++++++++++++++++
1 file changed, 141 insertions(+)
create mode 100644 include/linux/svsm_vtpm.h
diff --git a/include/linux/svsm_vtpm.h b/include/linux/svsm_vtpm.h
new file mode 100644
index 000000000000..2ce9b1cb827e
--- /dev/null
+++ b/include/linux/svsm_vtpm.h
@@ -0,0 +1,141 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2023 james.bottom...@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 _SVSM_VTPM_H_
+#define _SVSM_VTPM_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
+ */
+
+#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 SVSM_VTPM_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;
+
+/**
+ * svsm_vtpm_fill_cmd_req() - fill a struct tpm_send_cmd_req to be sent to SVSM
+ * @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
+svsm_vtpm_fill_cmd_req(struct tpm_send_cmd_req *req, u8 locality,
+ const u8 *buf, size_t len)
+{
+ if (len > SVSM_VTPM_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;
+}
+
+/**
+ * svsm_vtpm_parse_cmd_resp() - Parse a struct tpm_send_cmd_resp received from
+ * SVSM
+ * @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
+svsm_vtpm_parse_cmd_resp(const struct tpm_send_cmd_resp *resp, u8 *buf,
+ size_t len)
+{
+ if (len < resp->hdr.size)
+ return -E2BIG;
+
+ if (resp->hdr.size > SVSM_VTPM_MAX_BUFFER - sizeof(*resp))
+ return -EINVAL; // Invalid response from the platform TPM
+
+ memcpy(buf, resp->outbuf, resp->hdr.size);
+
+ return resp->hdr.size;
+}
+
+#endif /* _SVSM_VTPM_H_ */
--
2.48.1
