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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
*
* Driver for the vTPM defined by the AMD SVSM spec [1].
*
* The specification defines a protocol that a SEV-SNP guest OS can use to
* discover and talk to a vTPM emulated by the Secure VM Service Module (SVSM)
* in the guest context, but at a more privileged level (usually VMPL0).
*
* [1] "Secure VM Service Module for SEV-SNP Guests"
* Publication # 58019 Revision: 1.00
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/platform_device.h>
#include <linux/tpm_svsm.h>
#include <asm/sev.h>
#include "tpm.h"
struct tpm_svsm_priv {
void *buffer;
};
static int tpm_svsm_send(struct tpm_chip *chip, u8 *buf, size_t len)
{
struct tpm_svsm_priv *priv = dev_get_drvdata(&chip->dev);
int ret;
ret = svsm_vtpm_cmd_request_fill(priv->buffer, 0, buf, len);
if (ret)
return ret;
/*
* The SVSM call uses the same buffer for the command and for the
* response, so after this call, the buffer will contain the response
* that can be used by .recv() op.
*/
return snp_svsm_vtpm_send_command(priv->buffer);
}
static int tpm_svsm_recv(struct tpm_chip *chip, u8 *buf, size_t len)
{
struct tpm_svsm_priv *priv = dev_get_drvdata(&chip->dev);
/*
* The internal buffer contains the response after we send the command
* to SVSM.
*/
return svsm_vtpm_cmd_response_parse(priv->buffer, buf, len);
}
static struct tpm_class_ops tpm_chip_ops = {
.flags = TPM_OPS_AUTO_STARTUP,
.recv = tpm_svsm_recv,
.send = tpm_svsm_send,
};
static int __init tpm_svsm_probe(struct platform_device *pdev)
{
struct device *dev = &pdev->dev;
struct tpm_svsm_priv *priv;
struct tpm_chip *chip;
int err;
priv = devm_kmalloc(dev, sizeof(*priv), GFP_KERNEL);
if (!priv)
return -ENOMEM;
/*
* The maximum buffer supported is one page (see SVSM_VTPM_MAX_BUFFER
* in tpm_svsm.h).
*/
priv->buffer = (void *)devm_get_free_pages(dev, GFP_KERNEL, 0);
if (!priv->buffer)
return -ENOMEM;
chip = tpmm_chip_alloc(dev, &tpm_chip_ops);
if (IS_ERR(chip))
return PTR_ERR(chip);
dev_set_drvdata(&chip->dev, priv);
err = tpm2_probe(chip);
if (err)
return err;
err = tpm_chip_register(chip);
if (err)
return err;
dev_info(dev, "SNP SVSM vTPM %s device\n",
(chip->flags & TPM_CHIP_FLAG_TPM2) ? "2.0" : "1.2");
return 0;
}
static void __exit tpm_svsm_remove(struct platform_device *pdev)
{
struct tpm_chip *chip = platform_get_drvdata(pdev);
tpm_chip_unregister(chip);
}
/*
* tpm_svsm_remove() lives in .exit.text. For drivers registered via
* module_platform_driver_probe() this is ok because they cannot get unbound
* at runtime. So mark the driver struct with __refdata to prevent modpost
* triggering a section mismatch warning.
*/
static struct platform_driver tpm_svsm_driver __refdata = {
.remove = __exit_p(tpm_svsm_remove),
.driver = {
.name = "tpm-svsm",
},
};
module_platform_driver_probe(tpm_svsm_driver, tpm_svsm_probe);
MODULE_DESCRIPTION("SNP SVSM vTPM Driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:tpm-svsm");
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