On Fri, Feb 28, 2025 at 06:07:19PM +0100, Stefano Garzarella wrote: > 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 two functions exposed by x86/sev > to verify that the device is actually emulated by the platform and to > send commands and receive responses. > > The vTPM is emulated through the TCG reference implementation, so this > driver leverages tpm_tcgsim.h to fill commands and parse responses. Why? Please don't. > > The device cannot be hot-plugged/unplugged as it is emulated by the > platform, so we can use module_platform_driver_probe(). The probe > function will only check whether in the current runtime configuration, > SVSM is present and provides a vTPM. > > [1] "Secure VM Service Module for SEV-SNP Guests" > Publication # 58019 Revision: 1.00 > https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/58019.pdf > > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx> > --- > drivers/char/tpm/tpm_svsm.c | 120 ++++++++++++++++++++++++++++++++++++ > drivers/char/tpm/Kconfig | 10 +++ > drivers/char/tpm/Makefile | 1 + > 3 files changed, 131 insertions(+) > create mode 100644 drivers/char/tpm/tpm_svsm.c > > diff --git a/drivers/char/tpm/tpm_svsm.c b/drivers/char/tpm/tpm_svsm.c > new file mode 100644 > index 000000000000..1c34133990c5 > --- /dev/null > +++ b/drivers/char/tpm/tpm_svsm.c > @@ -0,0 +1,120 @@ > +// 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). > + * > + * The vTPM is emulated through the TCG reference implementation, so this > + * driver leverages tpm_tcgsim.h to fill commands and parse responses. > + * > + * [1] "Secure VM Service Module for SEV-SNP Guests" > + * Publication # 58019 Revision: 1.00 > + * https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/58019.pdf > + */ > + > +#include <asm/sev.h> > +#include <linux/module.h> > +#include <linux/kernel.h> > +#include <linux/platform_device.h> > +#include <linux/tpm_tcgsim.h> > + > +#include "tpm.h" > + > +struct tpm_svsm_priv { > + u8 buffer[TPM_TCGSIM_MAX_BUFFER]; > + u8 locality; > +}; > + > +static int tpm_svsm_send_recv(struct tpm_chip *chip, u8 *buf, size_t buf_len, > + size_t to_send) > +{ > + struct tpm_svsm_priv *priv = dev_get_drvdata(&chip->dev); > + int ret; > + > + ret = tpm_tcgsim_fill_send_cmd((struct tpm_send_cmd_req *)priv->buffer, > + priv->locality, buf, to_send); > + if (ret) > + return ret; > + > + ret = snp_svsm_vtpm_send_command(priv->buffer); > + if (ret) > + return ret; > + > + return tpm_tcgsim_parse_send_cmd((struct tpm_send_cmd_resp *)priv->buffer, > + buf, buf_len); > +} > + > +static struct tpm_class_ops tpm_chip_ops = { > + .flags = TPM_OPS_AUTO_STARTUP, > + .send_recv = tpm_svsm_send_recv, > +}; > + > +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; > + > + if (!snp_svsm_vtpm_probe()) > + return -ENODEV; > + > + priv = devm_kmalloc(dev, sizeof(*priv), GFP_KERNEL); > + if (!priv) > + return -ENOMEM; > + > + /* > + * FIXME: before implementing locality we need to agree what it means > + * for the SNP SVSM vTPM > + */ > + priv->locality = 0; > + > + 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"); > diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig > index 0fc9a510e059..fc3f1d10d31d 100644 > --- a/drivers/char/tpm/Kconfig > +++ b/drivers/char/tpm/Kconfig > @@ -225,5 +225,15 @@ 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 9bb142c75243..52d9d80a0f56 100644 > --- a/drivers/char/tpm/Makefile > +++ b/drivers/char/tpm/Makefile > @@ -44,3 +44,4 @@ obj-$(CONFIG_TCG_XEN) += xen-tpmfront.o > obj-$(CONFIG_TCG_CRB) += tpm_crb.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 > -- > 2.48.1 > OK, so this is like ARM's driver architecture using SMC, and I think tpm_ftpm_tee is probably one great reflection for this overall. Is this correct analysis, or not? BR, Jarkko
