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Message-ID: <174436654133.31282.1172867310137729031.tip-bot2@tip-bot2>
Date: Fri, 11 Apr 2025 10:15:41 -0000
From: "tip-bot2 for Stefano Garzarella" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Stefano Garzarella <sgarzare@...hat.com>,
"Borislav Petkov (AMD)" <bp@...en8.de>, Jarkko Sakkinen <jarkko@...nel.org>,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/sev] tpm: Add SNP SVSM vTPM driver
The following commit has been merged into the x86/sev branch of tip:
Commit-ID: 93b7c6b3ce918c3d24de82dcff7a87b8bd631b2e
Gitweb: https://git.kernel.org/tip/93b7c6b3ce918c3d24de82dcff7a87b8bd631b2e
Author: Stefano Garzarella <sgarzare@...hat.com>
AuthorDate: Thu, 10 Apr 2025 15:51:15 +02:00
Committer: Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Thu, 10 Apr 2025 16:24:29 +02:00
tpm: Add SNP SVSM vTPM driver
Add 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 (VMPL0).
The new tpm-svsm platform driver uses API exposed by the x86/sev core
implementation interface to a SVSM to send commands and receive responses.
The device cannot be hot-plugged/unplugged as it is emulated by the platform,
so module_platform_driver_probe() can be used. The device will be registered
by the platform only when it's available, so the probe function just needs to
setup the tpm_chip.
This device does not support interrupts and sends responses to commands
synchronously.
In order to have .recv() called just after .send() in tpm_try_transmit(), the
.status() callback is not implemented as recently supported by commit
980a573621ea ("tpm: Make chip->{status,cancel,req_canceled} opt").
[1] "Secure VM Service Module for SEV-SNP Guests"
Publication # 58019 Revision: 1.00
[ bp: Massage commit message. ]
Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
Link: https://lore.kernel.org/r/20250410135118.133240-4-sgarzare@redhat.com
---
drivers/char/tpm/Kconfig | 10 +++-
drivers/char/tpm/Makefile | 1 +-
drivers/char/tpm/tpm_svsm.c | 125 +++++++++++++++++++++++++++++++++++-
3 files changed, 136 insertions(+)
create mode 100644 drivers/char/tpm/tpm_svsm.c
diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
index fe4f3a6..dddd702 100644
--- a/drivers/char/tpm/Kconfig
+++ b/drivers/char/tpm/Kconfig
@@ -234,5 +234,15 @@ config TCG_FTPM_TEE
help
This driver proxies for firmware TPM running in TEE.
+config TCG_SVSM
+ tristate "SNP SVSM vTPM interface"
+ depends on AMD_MEM_ENCRYPT
+ help
+ This is a driver for the AMD SVSM vTPM 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). To compile this driver as a module, choose M
+ here; the module will be called tpm_svsm.
+
source "drivers/char/tpm/st33zp24/Kconfig"
endif # TCG_TPM
diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile
index 2b004df..9de1b3e 100644
--- a/drivers/char/tpm/Makefile
+++ b/drivers/char/tpm/Makefile
@@ -45,3 +45,4 @@ obj-$(CONFIG_TCG_CRB) += tpm_crb.o
obj-$(CONFIG_TCG_ARM_CRB_FFA) += tpm_crb_ffa.o
obj-$(CONFIG_TCG_VTPM_PROXY) += tpm_vtpm_proxy.o
obj-$(CONFIG_TCG_FTPM_TEE) += tpm_ftpm_tee.o
+obj-$(CONFIG_TCG_SVSM) += tpm_svsm.o
diff --git a/drivers/char/tpm/tpm_svsm.c b/drivers/char/tpm/tpm_svsm.c
new file mode 100644
index 0000000..4280edf
--- /dev/null
+++ b/drivers/char/tpm/tpm_svsm.c
@@ -0,0 +1,125 @@
+// 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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