Date:   Mon, 16 May 2022 16:51:06 +0200
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     Steffen Eiden <seiden@...ux.ibm.com>
Cc:     Greg KH <greg@...ah.com>, Heiko Carstens <hca@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Shuah Khan <shuah@...nel.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Nico Boehr <nrb@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v4 1/2] drivers/s390/char: Add Ultravisor io device

On Mon, 16 May 2022 11:33:35 +0000
Steffen Eiden <seiden@...ux.ibm.com> wrote:

> This patch adds a new miscdevice to expose some Ultravisor functions
> to userspace. Userspace can send IOCTLs to the uvdevice that will then
> emit a corresponding Ultravisor Call and hands the result over to
> userspace. The uvdevice is available if the Ultravisor Call facility is
> present.
> Userspace can call the Retrieve Attestation Measurement
> Ultravisor Call using IOCTLs on the uvdevice.
> 
> The uvdevice will do some sanity checks first.
> Then, copy the request data to kernel space, build the UVCB,
> perform the UV call, and copy the result back to userspace.
> 
> Signed-off-by: Steffen Eiden <seiden@...ux.ibm.com>
> Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>

Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>

> ---
> After some private discussion "struct uvio_ioctl_cb uv_ioctl"
> in "uvio_ioctl()" is now in the stack.
> 
>  MAINTAINERS                           |   2 +
>  arch/s390/include/asm/uv.h            |  23 ++-
>  arch/s390/include/uapi/asm/uvdevice.h |  51 +++++
>  drivers/s390/char/Kconfig             |  10 +
>  drivers/s390/char/Makefile            |   1 +
>  drivers/s390/char/uvdevice.c          | 257 ++++++++++++++++++++++++++
>  6 files changed, 343 insertions(+), 1 deletion(-)
>  create mode 100644 arch/s390/include/uapi/asm/uvdevice.h
>  create mode 100644 drivers/s390/char/uvdevice.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index e8c52d0192a6..b42ab4a35e18 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -10781,9 +10781,11 @@ F:	Documentation/virt/kvm/s390*
>  F:	arch/s390/include/asm/gmap.h
>  F:	arch/s390/include/asm/kvm*
>  F:	arch/s390/include/uapi/asm/kvm*
> +F:	arch/s390/include/uapi/asm/uvdevice.h
>  F:	arch/s390/kernel/uv.c
>  F:	arch/s390/kvm/
>  F:	arch/s390/mm/gmap.c
> +F:	drivers/s390/char/uvdevice.c
>  F:	tools/testing/selftests/kvm/*/s390x/
>  F:	tools/testing/selftests/kvm/s390x/
>  
> diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
> index a2d376b8bce3..cfea7b77a5b8 100644
> --- a/arch/s390/include/asm/uv.h
> +++ b/arch/s390/include/asm/uv.h
> @@ -2,7 +2,7 @@
>  /*
>   * Ultravisor Interfaces
>   *
> - * Copyright IBM Corp. 2019
> + * Copyright IBM Corp. 2019, 2022
>   *
>   * Author(s):
>   *	Vasily Gorbik <gor@...ux.ibm.com>
> @@ -52,6 +52,7 @@
>  #define UVC_CMD_UNPIN_PAGE_SHARED	0x0342
>  #define UVC_CMD_SET_SHARED_ACCESS	0x1000
>  #define UVC_CMD_REMOVE_SHARED_ACCESS	0x1001
> +#define UVC_CMD_RETR_ATTEST		0x1020
>  
>  /* Bits in installed uv calls */
>  enum uv_cmds_inst {
> @@ -76,6 +77,7 @@ enum uv_cmds_inst {
>  	BIT_UVC_CMD_UNSHARE_ALL = 20,
>  	BIT_UVC_CMD_PIN_PAGE_SHARED = 21,
>  	BIT_UVC_CMD_UNPIN_PAGE_SHARED = 22,
> +	BIT_UVC_CMD_RETR_ATTEST = 28,
>  };
>  
>  enum uv_feat_ind {
> @@ -219,6 +221,25 @@ struct uv_cb_share {
>  	u64 reserved28;
>  } __packed __aligned(8);
>  
> +/* Retrieve Attestation Measurement */
> +struct uv_cb_attest {
> +	struct uv_cb_header header;	/* 0x0000 */
> +	u64 reserved08[2];		/* 0x0008 */
> +	u64 arcb_addr;			/* 0x0018 */
> +	u64 cont_token;			/* 0x0020 */
> +	u8  reserved28[6];		/* 0x0028 */
> +	u16 user_data_len;		/* 0x002e */
> +	u8  user_data[256];		/* 0x0030 */
> +	u32 reserved130[3];		/* 0x0130 */
> +	u32 meas_len;			/* 0x013c */
> +	u64 meas_addr;			/* 0x0140 */
> +	u8  config_uid[16];		/* 0x0148 */
> +	u32 reserved158;		/* 0x0158 */
> +	u32 add_data_len;		/* 0x015c */
> +	u64 add_data_addr;		/* 0x0160 */
> +	u64 reserved168[4];		/* 0x0168 */
> +} __packed __aligned(8);
> +
>  static inline int __uv_call(unsigned long r1, unsigned long r2)
>  {
>  	int cc;
> diff --git a/arch/s390/include/uapi/asm/uvdevice.h b/arch/s390/include/uapi/asm/uvdevice.h
> new file mode 100644
> index 000000000000..d0bdde4969a1
> --- /dev/null
> +++ b/arch/s390/include/uapi/asm/uvdevice.h
> @@ -0,0 +1,51 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + *  Copyright IBM Corp. 2022
> + *  Author(s): Steffen Eiden <seiden@...ux.ibm.com>
> + */
> +#ifndef __S390_ASM_UVDEVICE_H
> +#define __S390_ASM_UVDEVICE_H
> +
> +#include <linux/types.h>
> +
> +struct uvio_ioctl_cb {
> +	__u32 flags;
> +	__u16 uv_rc;			/* UV header rc value */
> +	__u16 uv_rrc;			/* UV header rrc value */
> +	__u64 argument_addr;		/* Userspace address of uvio argument */
> +	__u32 argument_len;
> +	__u8  reserved14[0x40 - 0x14];	/* must be zero */
> +};
> +
> +#define UVIO_ATT_USER_DATA_LEN		0x100
> +#define UVIO_ATT_UID_LEN		0x10
> +struct uvio_attest {
> +	__u64 arcb_addr;				/* 0x0000 */
> +	__u64 meas_addr;				/* 0x0008 */
> +	__u64 add_data_addr;				/* 0x0010 */
> +	__u8  user_data[UVIO_ATT_USER_DATA_LEN];	/* 0x0018 */
> +	__u8  config_uid[UVIO_ATT_UID_LEN];		/* 0x0118 */
> +	__u32 arcb_len;					/* 0x0128 */
> +	__u32 meas_len;					/* 0x012c */
> +	__u32 add_data_len;				/* 0x0130 */
> +	__u16 user_data_len;				/* 0x0134 */
> +	__u16 reserved136;				/* 0x0136 */
> +};
> +
> +/*
> + * The following max values define an upper length for the IOCTL in/out buffers.
> + * However, they do not represent the maximum the Ultravisor allows which is
> + * often way smaller. By allowing larger buffer sizes we hopefully do not need
> + * to update the code with every machine update. It is therefore possible for
> + * userspace to request more memory than actually used by kernel/UV.
> + */
> +#define UVIO_ATT_ARCB_MAX_LEN		0x100000
> +#define UVIO_ATT_MEASUREMENT_MAX_LEN	0x8000
> +#define UVIO_ATT_ADDITIONAL_MAX_LEN	0x8000
> +
> +#define UVIO_DEVICE_NAME "uv"
> +#define UVIO_TYPE_UVC 'u'
> +
> +#define UVIO_IOCTL_ATT _IOWR(UVIO_TYPE_UVC, 0x01, struct uvio_ioctl_cb)
> +
> +#endif  /* __S390_ASM_UVDEVICE_H */
> diff --git a/drivers/s390/char/Kconfig b/drivers/s390/char/Kconfig
> index 6cc4b19acf85..e9b9902abbaf 100644
> --- a/drivers/s390/char/Kconfig
> +++ b/drivers/s390/char/Kconfig
> @@ -100,6 +100,16 @@ config SCLP_OFB
>  	  This option enables the Open-for-Business interface to the s390
>  	  Service Element.
>  
> +config S390_UV_UAPI
> +	def_tristate y
> +	prompt "Ultravisor userspace API"
> +	help
> +	  Selecting exposes parts of the UV interface to userspace
> +	  by providing a misc character device at /dev/uv.
> +	  Using IOCTLs one can interact with the UV.
> +	  The device is only available if the Ultravisor
> +	  Facility (158) is present.
> +
>  config S390_TAPE
>  	def_tristate m
>  	prompt "S/390 tape device support"
> diff --git a/drivers/s390/char/Makefile b/drivers/s390/char/Makefile
> index c6fdb81a068a..ce32270082f5 100644
> --- a/drivers/s390/char/Makefile
> +++ b/drivers/s390/char/Makefile
> @@ -48,6 +48,7 @@ obj-$(CONFIG_MONREADER) += monreader.o
>  obj-$(CONFIG_MONWRITER) += monwriter.o
>  obj-$(CONFIG_S390_VMUR) += vmur.o
>  obj-$(CONFIG_CRASH_DUMP) += sclp_sdias.o zcore.o
> +obj-$(CONFIG_S390_UV_UAPI) += uvdevice.o
>  
>  hmcdrv-objs := hmcdrv_mod.o hmcdrv_dev.o hmcdrv_ftp.o hmcdrv_cache.o diag_ftp.o sclp_ftp.o
>  obj-$(CONFIG_HMC_DRV) += hmcdrv.o
> diff --git a/drivers/s390/char/uvdevice.c b/drivers/s390/char/uvdevice.c
> new file mode 100644
> index 000000000000..e8e1409df015
> --- /dev/null
> +++ b/drivers/s390/char/uvdevice.c
> @@ -0,0 +1,257 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + *  Copyright IBM Corp. 2022
> + *  Author(s): Steffen Eiden <seiden@...ux.ibm.com>
> + *
> + *  This file provides a Linux misc device to give userspace access to some
> + *  Ultravisor (UV) functions. The device only accepts IOCTLs and will only
> + *  be present if the Ultravisor facility (158) is present.
> + *
> + *  When userspace sends a valid IOCTL uvdevice will copy the input data to
> + *  kernel space, do some basic validity checks to avoid kernel/system
> + *  corruption. Any other check that the Ultravisor does will not be done by
> + *  the uvdevice to keep changes minimal when adding new functionalities
> + *  to existing UV-calls.
> + *  After the checks uvdevice builds a corresponding
> + *  Ultravisor Call Control Block, and sends the request to the Ultravisor.
> + *  Then, it copies the response, including the return codes, back to userspace.
> + *  It is the responsibility of the userspace to check for any error issued
> + *  by UV and to interpret the UV response. The uvdevice acts as a communication
> + *  channel for userspace to the Ultravisor.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/miscdevice.h>
> +#include <linux/types.h>
> +#include <linux/stddef.h>
> +#include <linux/vmalloc.h>
> +#include <linux/slab.h>
> +
> +#include <asm/uvdevice.h>
> +#include <asm/uv.h>
> +
> +static int uvio_build_uvcb_attest(struct uv_cb_attest *uvcb_attest, u8 *arcb,
> +				  u8 *meas, u8 *add_data, struct uvio_attest *uvio_attest)
> +{
> +	void __user *user_buf_arcb = (void __user *)uvio_attest->arcb_addr;
> +
> +	if (copy_from_user(arcb, user_buf_arcb, uvio_attest->arcb_len))
> +		return -EFAULT;
> +
> +	uvcb_attest->header.len = sizeof(*uvcb_attest);
> +	uvcb_attest->header.cmd = UVC_CMD_RETR_ATTEST;
> +	uvcb_attest->arcb_addr = (u64)arcb;
> +	uvcb_attest->cont_token = 0;
> +	uvcb_attest->user_data_len = uvio_attest->user_data_len;
> +	memcpy(uvcb_attest->user_data, uvio_attest->user_data, sizeof(uvcb_attest->user_data));
> +	uvcb_attest->meas_len = uvio_attest->meas_len;
> +	uvcb_attest->meas_addr = (u64)meas;
> +	uvcb_attest->add_data_len = uvio_attest->add_data_len;
> +	uvcb_attest->add_data_addr = (u64)add_data;
> +
> +	return 0;
> +}
> +
> +static int uvio_copy_attest_result_to_user(struct uv_cb_attest *uvcb_attest,
> +					   struct uvio_ioctl_cb *uv_ioctl,
> +					   u8 *measurement, u8 *add_data,
> +					   struct uvio_attest *uvio_attest)
> +{
> +	struct uvio_attest __user *user_uvio_attest = (void __user *)uv_ioctl->argument_addr;
> +	void __user *user_buf_add = (void __user *)uvio_attest->add_data_addr;
> +	void __user *user_buf_meas = (void __user *)uvio_attest->meas_addr;
> +	void __user *user_buf_uid = &user_uvio_attest->config_uid;
> +
> +	if (copy_to_user(user_buf_meas, measurement, uvio_attest->meas_len))
> +		return -EFAULT;
> +	if (add_data && copy_to_user(user_buf_add, add_data, uvio_attest->add_data_len))
> +		return -EFAULT;
> +	if (copy_to_user(user_buf_uid, uvcb_attest->config_uid, sizeof(uvcb_attest->config_uid)))
> +		return -EFAULT;
> +	return 0;
> +}
> +
> +static int get_uvio_attest(struct uvio_ioctl_cb *uv_ioctl, struct uvio_attest *uvio_attest)
> +{
> +	u8 __user *user_arg_buf = (u8 __user *)uv_ioctl->argument_addr;
> +
> +	if (copy_from_user(uvio_attest, user_arg_buf, sizeof(*uvio_attest)))
> +		return -EFAULT;
> +
> +	if (uvio_attest->arcb_len > UVIO_ATT_ARCB_MAX_LEN)
> +		return -EINVAL;
> +	if (uvio_attest->arcb_len == 0)
> +		return -EINVAL;
> +	if (uvio_attest->meas_len > UVIO_ATT_MEASUREMENT_MAX_LEN)
> +		return -EINVAL;
> +	if (uvio_attest->meas_len == 0)
> +		return -EINVAL;
> +	if (uvio_attest->add_data_len > UVIO_ATT_ADDITIONAL_MAX_LEN)
> +		return -EINVAL;
> +	if (uvio_attest->reserved136)
> +		return -EINVAL;
> +	return 0;
> +}
> +
> +/**
> + * uvio_attestation() - Perform a Retrieve Attestation Measurement UVC.
> + *
> + * @uv_ioctl: ioctl control block
> + *
> + * uvio_attestation() does a  Retrieve Attestation Measurement Ultravisor Call.
> + * It verifies that the given userspace addresses are valid and request sizes
> + * are sane. Every other check is made by the Ultravisor (UV) and won't result
> + * in a negative return value. It copies the input to kernelspace, builds the
> + * request, sends the UV-call, and copies the result to userspace.
> + *
> + * The Attestation Request has two input and two outputs.
> + * ARCB and User Data are inputs for the UV generated by userspace.
> + * Measurement and Additional Data are outputs for userspace generated by UV.
> + *
> + * The Attestation Request Control Block (ARCB) is a cryptographically verified
> + * and secured request to UV and User Data is some plaintext data which is
> + * going to be included in the Attestation Measurement calculation.
> + *
> + * Measurement is a cryptographic measurement of the callers properties,
> + * optional data configured by the ARCB and the user data. If specified by the
> + * ARCB, UV will add some Additional Data to the measurement calculation.
> + * This Additional Data is then returned as well.
> + *
> + * If the Retrieve Attestation Measurement UV facility is not present,
> + * UV will return invalid command rc. This won't be fenced in the driver
> + * and does not result in a negative return value.
> + *
> + * Context: might sleep
> + *
> + * Return: 0 on success or a negative error code on error.
> + */
> +static int uvio_attestation(struct uvio_ioctl_cb *uv_ioctl)
> +{
> +	struct uv_cb_attest *uvcb_attest = NULL;
> +	struct uvio_attest *uvio_attest = NULL;
> +	u8 *measurement = NULL;
> +	u8 *add_data = NULL;
> +	u8 *arcb = NULL;
> +	int ret;
> +
> +	ret = -EINVAL;
> +	if (uv_ioctl->argument_len != sizeof(*uvio_attest))
> +		goto out;
> +
> +	ret = -ENOMEM;
> +	uvio_attest = kzalloc(sizeof(*uvio_attest), GFP_KERNEL);
> +	if (!uvio_attest)
> +		goto out;
> +
> +	ret = get_uvio_attest(uv_ioctl, uvio_attest);
> +	if (ret)
> +		goto out;
> +
> +	ret = -ENOMEM;
> +	arcb = kvzalloc(uvio_attest->arcb_len, GFP_KERNEL);
> +	measurement = kvzalloc(uvio_attest->meas_len, GFP_KERNEL);
> +	if (!arcb || !measurement)
> +		goto out;
> +
> +	if (uvio_attest->add_data_len) {
> +		add_data = kvzalloc(uvio_attest->add_data_len, GFP_KERNEL);
> +		if (!add_data)
> +			goto out;
> +	}
> +
> +	uvcb_attest = kzalloc(sizeof(*uvcb_attest), GFP_KERNEL);
> +	if (!uvcb_attest)
> +		goto out;
> +
> +	ret = uvio_build_uvcb_attest(uvcb_attest, arcb,  measurement, add_data, uvio_attest);
> +	if (ret)
> +		goto out;
> +
> +	uv_call_sched(0, (u64)uvcb_attest);
> +
> +	uv_ioctl->uv_rc = uvcb_attest->header.rc;
> +	uv_ioctl->uv_rrc = uvcb_attest->header.rrc;
> +
> +	ret = uvio_copy_attest_result_to_user(uvcb_attest, uv_ioctl, measurement, add_data,
> +					      uvio_attest);
> +out:
> +	kvfree(arcb);
> +	kvfree(measurement);
> +	kvfree(add_data);
> +	kfree(uvio_attest);
> +	kfree(uvcb_attest);
> +	return ret;
> +}
> +
> +static int uvio_copy_and_check_ioctl(struct uvio_ioctl_cb *ioctl, void __user *argp)
> +{
> +	if (copy_from_user(ioctl, argp, sizeof(*ioctl)))
> +		return -EFAULT;
> +	if (ioctl->flags != 0)
> +		return -EINVAL;
> +	if (memchr_inv(ioctl->reserved14, 0, sizeof(ioctl->reserved14)))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +/*
> + * IOCTL entry point for the Ultravisor device.
> + */
> +static long uvio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> +{
> +	void __user *argp = (void __user *)arg;
> +	struct uvio_ioctl_cb uv_ioctl = { };
> +	long ret;
> +
> +	switch (cmd) {
> +	case UVIO_IOCTL_ATT:
> +		ret = uvio_copy_and_check_ioctl(&uv_ioctl, argp);
> +		if (ret)
> +			return ret;
> +		ret = uvio_attestation(&uv_ioctl);
> +		break;
> +	default:
> +		ret = -ENOIOCTLCMD;
> +		break;
> +	}
> +	if (ret)
> +		return ret;
> +
> +	if (copy_to_user(argp, &uv_ioctl, sizeof(uv_ioctl)))
> +		ret = -EFAULT;
> +
> +	return ret;
> +}
> +
> +static const struct file_operations uvio_dev_fops = {
> +	.owner = THIS_MODULE,
> +	.unlocked_ioctl = uvio_ioctl,
> +	.llseek = no_llseek,
> +};
> +
> +static struct miscdevice uvio_dev_miscdev = {
> +	.minor = MISC_DYNAMIC_MINOR,
> +	.name = UVIO_DEVICE_NAME,
> +	.fops = &uvio_dev_fops,
> +};
> +
> +static void __exit uvio_dev_exit(void)
> +{
> +	misc_deregister(&uvio_dev_miscdev);
> +}
> +
> +static int __init uvio_dev_init(void)
> +{
> +	if (!test_facility(158))
> +		return -ENXIO;
> +	return misc_register(&uvio_dev_miscdev);
> +}
> +
> +module_init(uvio_dev_init);
> +module_exit(uvio_dev_exit);
> +
> +MODULE_AUTHOR("IBM Corporation");
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("Ultravisor UAPI driver");

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