Commit ccadf154 authored by Russell Currey's avatar Russell Currey Committed by Michael Ellerman
Browse files

powerpc/pseries: Implement secvars for dynamic secure boot 



The pseries platform can support dynamic secure boot (i.e. secure boot
using user-defined keys) using variables contained with the PowerVM LPAR
Platform KeyStore (PLPKS).  Using the powerpc secvar API, expose the
relevant variables for pseries dynamic secure boot through the existing
secvar filesystem layout.

The relevant variables for dynamic secure boot are signed in the
keystore, and can only be modified using the H_PKS_SIGNED_UPDATE hcall.
Object labels in the keystore are encoded using ucs2 format.  With our
fixed variable names we don't have to care about encoding outside of the
necessary byte padding.

When a user writes to a variable, the first 8 bytes of data must contain
the signed update flags as defined by the hypervisor.

When a user reads a variable, the first 4 bytes of data contain the
policies defined for the object.

Limitations exist due to the underlying implementation of sysfs binary
attributes, as is the case for the OPAL secvar implementation -
partial writes are unsupported and writes cannot be larger than PAGE_SIZE.
(Even when using bin_attributes, which can be larger than a single page,
sysfs only gives us one page's worth of write buffer at a time, and the
hypervisor does not expose an interface for partial writes.)

Co-developed-by: default avatarNayna Jain <nayna@linux.ibm.com>
Signed-off-by: default avatarNayna Jain <nayna@linux.ibm.com>
Co-developed-by: default avatarAndrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: default avatarAndrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: default avatarRussell Currey <ruscur@russell.cc>
[mpe: Add NLS dependency to fix build errors, squash fix from ajd]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230210080401.345462-25-ajd@linux.ibm.com
parent 91361b51

Documentation/ABI/testing/sysfs-secvar

+74 −1
Original line number Diff line number Diff line
@@ -18,6 +18,14 @@ Description: A string indicating which backend is in use by the firmware. 
		This determines the format of the variable and the accepted

		format of variable updates.



		On powernv/OPAL, this value is provided by the OPAL firmware

		and is expected to be "ibm,edk2-compat-v1".



		On pseries/PLPKS, this is generated by the kernel based on the

		version number in the SB_VERSION variable in the keystore, and

		has the form "ibm,plpks-sb-v<version>", or

		"ibm,plpks-sb-unknown" if there is no SB_VERSION variable.



What:		/sys/firmware/secvar/vars/<variable name>

Date:		August 2019

Contact:	Nayna Jain <nayna@linux.ibm.com>
@@ -34,7 +42,7 @@ Description: An integer representation of the size of the content of the 


What:		/sys/firmware/secvar/vars/<variable_name>/data

Date:		August 2019

Contact:	Nayna Jain h<nayna@linux.ibm.com>

Contact:	Nayna Jain <nayna@linux.ibm.com>

Description:	A read-only file containing the value of the variable. The size

		of the file represents the maximum size of the variable data.
@@ -44,3 +52,68 @@ Contact: Nayna Jain <nayna@linux.ibm.com> 
Description:	A write-only file that is used to submit the new value for the

		variable. The size of the file represents the maximum size of

		the variable data that can be written.



What:		/sys/firmware/secvar/config

Date:		February 2023

Contact:	Nayna Jain <nayna@linux.ibm.com>

Description:	This optional directory contains read-only config attributes as

		defined by the secure variable implementation.  All data is in

		ASCII format. The directory is only created if the backing

		implementation provides variables to populate it, which at

		present is only PLPKS on the pseries platform.



What:		/sys/firmware/secvar/config/version

Date:		February 2023

Contact:	Nayna Jain <nayna@linux.ibm.com>

Description:	Config version as reported by the hypervisor in ASCII decimal

		format.



		Currently only provided by PLPKS on the pseries platform.



What:		/sys/firmware/secvar/config/max_object_size

Date:		February 2023

Contact:	Nayna Jain <nayna@linux.ibm.com>

Description:	Maximum allowed size of	objects in the keystore in bytes,

		represented in ASCII decimal format.



		This is not necessarily the same as the max size that can be

		written to an update file as writes can contain more than

		object data, you should use the size of the update file for

		that purpose.



		Currently only provided by PLPKS on the pseries platform.



What:		/sys/firmware/secvar/config/total_size

Date:		February 2023

Contact:	Nayna Jain <nayna@linux.ibm.com>

Description:	Total size of the PLPKS in bytes, represented in ASCII decimal

		format.



		Currently only provided by PLPKS on the pseries platform.



What:		/sys/firmware/secvar/config/used_space

Date:		February 2023

Contact:	Nayna Jain <nayna@linux.ibm.com>

Description:	Current space consumed by the key store, in bytes, represented

		in ASCII decimal format.



		Currently only provided by PLPKS on the pseries platform.



What:		/sys/firmware/secvar/config/supported_policies

Date:		February 2023

Contact:	Nayna Jain <nayna@linux.ibm.com>

Description:	Bitmask of supported policy flags by the hypervisor,

		represented as an 8 byte hexadecimal ASCII string. Consult the

		hypervisor documentation for what these flags are.



		Currently only provided by PLPKS on the pseries platform.



What:		/sys/firmware/secvar/config/signed_update_algorithms

Date:		February 2023

Contact:	Nayna Jain <nayna@linux.ibm.com>

Description:	Bitmask of flags indicating which algorithms the hypervisor

		supports for signed update of objects, represented as a 16 byte

		hexadecimal ASCII string. Consult the hypervisor documentation

		for what these flags mean.



		Currently only provided by PLPKS on the pseries platform.

arch/powerpc/platforms/pseries/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -151,6 +151,7 @@ config IBMEBUS 


config PSERIES_PLPKS

	depends on PPC_PSERIES

	select NLS

	bool

	# PowerVM provides an isolated Platform Keystore (PKS) storage

	# allocation for each LPAR with individually managed access

arch/powerpc/platforms/pseries/Makefile

+2 −2
Original line number Diff line number Diff line
@@ -28,7 +28,7 @@ obj-$(CONFIG_PPC_SPLPAR) += vphn.o 
obj-$(CONFIG_PPC_SVM)		+= svm.o

obj-$(CONFIG_FA_DUMP)		+= rtas-fadump.o

obj-$(CONFIG_PSERIES_PLPKS)	+= plpks.o



obj-$(CONFIG_PPC_SECURE_BOOT)	+= plpks-secvar.o

obj-$(CONFIG_SUSPEND)		+= suspend.o

obj-$(CONFIG_PPC_VAS)		+= vas.o vas-sysfs.o

arch/powerpc/platforms/pseries/plpks-secvar.c

0 → 100644
+216 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0-only



// Secure variable implementation using the PowerVM LPAR Platform KeyStore (PLPKS)

//

// Copyright 2022, 2023 IBM Corporation

// Authors: Russell Currey

//          Andrew Donnellan

//          Nayna Jain



#define pr_fmt(fmt) "secvar: "fmt



#include <linux/printk.h>

#include <linux/init.h>

#include <linux/types.h>

#include <linux/slab.h>

#include <linux/string.h>

#include <linux/kobject.h>

#include <linux/nls.h>

#include <asm/machdep.h>

#include <asm/secvar.h>

#include <asm/plpks.h>



// Config attributes for sysfs

#define PLPKS_CONFIG_ATTR(name, fmt, func)			\

	static ssize_t name##_show(struct kobject *kobj,	\

				   struct kobj_attribute *attr,	\

				   char *buf)			\

	{							\

		return sysfs_emit(buf, fmt, func());		\

	}							\

	static struct kobj_attribute attr_##name = __ATTR_RO(name)



PLPKS_CONFIG_ATTR(version, "%u\n", plpks_get_version);

PLPKS_CONFIG_ATTR(max_object_size, "%u\n", plpks_get_maxobjectsize);

PLPKS_CONFIG_ATTR(total_size, "%u\n", plpks_get_totalsize);

PLPKS_CONFIG_ATTR(used_space, "%u\n", plpks_get_usedspace);

PLPKS_CONFIG_ATTR(supported_policies, "%08x\n", plpks_get_supportedpolicies);

PLPKS_CONFIG_ATTR(signed_update_algorithms, "%016llx\n", plpks_get_signedupdatealgorithms);



static const struct attribute *config_attrs[] = {

	&attr_version.attr,

	&attr_max_object_size.attr,

	&attr_total_size.attr,

	&attr_used_space.attr,

	&attr_supported_policies.attr,

	&attr_signed_update_algorithms.attr,

	NULL,

};



static u32 get_policy(const char *name)

{

	if ((strcmp(name, "db") == 0) ||

	    (strcmp(name, "dbx") == 0) ||

	    (strcmp(name, "grubdb") == 0) ||

	    (strcmp(name, "grubdbx") == 0) ||

	    (strcmp(name, "sbat") == 0))

		return (PLPKS_WORLDREADABLE | PLPKS_SIGNEDUPDATE);

	else

		return PLPKS_SIGNEDUPDATE;

}



static const char * const plpks_var_names[] = {

	"PK",

	"KEK",

	"db",

	"dbx",

	"grubdb",

	"grubdbx",

	"sbat",

	"moduledb",

	"trustedcadb",

	NULL,

};



static int plpks_get_variable(const char *key, u64 key_len, u8 *data,

			      u64 *data_size)

{

	struct plpks_var var = {0};

	int rc = 0;



	// We subtract 1 from key_len because we don't need to include the

	// null terminator at the end of the string

	var.name = kcalloc(key_len - 1, sizeof(wchar_t), GFP_KERNEL);

	if (!var.name)

		return -ENOMEM;

	rc = utf8s_to_utf16s(key, key_len - 1, UTF16_LITTLE_ENDIAN, (wchar_t *)var.name,

			     key_len - 1);

	if (rc < 0)

		goto err;

	var.namelen = rc * 2;



	var.os = PLPKS_VAR_LINUX;

	if (data) {

		var.data = data;

		var.datalen = *data_size;

	}

	rc = plpks_read_os_var(&var);



	if (rc)

		goto err;



	*data_size = var.datalen;



err:

	kfree(var.name);

	if (rc && rc != -ENOENT) {

		pr_err("Failed to read variable '%s': %d\n", key, rc);

		// Return -EIO since userspace probably doesn't care about the

		// specific error

		rc = -EIO;

	}

	return rc;

}



static int plpks_set_variable(const char *key, u64 key_len, u8 *data,

			      u64 data_size)

{

	struct plpks_var var = {0};

	int rc = 0;

	u64 flags;



	// Secure variables need to be prefixed with 8 bytes of flags.

	// We only want to perform the write if we have at least one byte of data.

	if (data_size <= sizeof(flags))

		return -EINVAL;



	// We subtract 1 from key_len because we don't need to include the

	// null terminator at the end of the string

	var.name = kcalloc(key_len - 1, sizeof(wchar_t), GFP_KERNEL);

	if (!var.name)

		return -ENOMEM;

	rc = utf8s_to_utf16s(key, key_len - 1, UTF16_LITTLE_ENDIAN, (wchar_t *)var.name,

			     key_len - 1);

	if (rc < 0)

		goto err;

	var.namelen = rc * 2;



	memcpy(&flags, data, sizeof(flags));



	var.datalen = data_size - sizeof(flags);

	var.data = data + sizeof(flags);

	var.os = PLPKS_VAR_LINUX;

	var.policy = get_policy(key);



	// Unlike in the read case, the plpks error code can be useful to

	// userspace on write, so we return it rather than just -EIO

	rc = plpks_signed_update_var(&var, flags);



err:

	kfree(var.name);

	return rc;

}



// PLPKS dynamic secure boot doesn't give us a format string in the same way OPAL does.

// Instead, report the format using the SB_VERSION variable in the keystore.

// The string is made up by us, and takes the form "ibm,plpks-sb-v<n>" (or "ibm,plpks-sb-unknown"

// if the SB_VERSION variable doesn't exist). Hypervisor defines the SB_VERSION variable as a

// "1 byte unsigned integer value".

static ssize_t plpks_secvar_format(char *buf, size_t bufsize)

{

	struct plpks_var var = {0};

	ssize_t ret;

	u8 version;



	var.component = NULL;

	// Only the signed variables have null bytes in their names, this one doesn't

	var.name = "SB_VERSION";

	var.namelen = strlen(var.name);

	var.datalen = 1;

	var.data = &version;



	// Unlike the other vars, SB_VERSION is owned by firmware instead of the OS

	ret = plpks_read_fw_var(&var);

	if (ret) {

		if (ret == -ENOENT) {

			ret = snprintf(buf, bufsize, "ibm,plpks-sb-unknown");

		} else {

			pr_err("Error %ld reading SB_VERSION from firmware\n", ret);

			ret = -EIO;

		}

		goto err;

	}



	ret = snprintf(buf, bufsize, "ibm,plpks-sb-v%hhu", version);

err:

	return ret;

}



static int plpks_max_size(u64 *max_size)

{

	// The max object size reported by the hypervisor is accurate for the

	// object itself, but we use the first 8 bytes of data on write as the

	// signed update flags, so the max size a user can write is larger.

	*max_size = (u64)plpks_get_maxobjectsize() + sizeof(u64);



	return 0;

}





static const struct secvar_operations plpks_secvar_ops = {

	.get = plpks_get_variable,

	.set = plpks_set_variable,

	.format = plpks_secvar_format,

	.max_size = plpks_max_size,

	.config_attrs = config_attrs,

	.var_names = plpks_var_names,

};



static int plpks_secvar_init(void)

{

	if (!plpks_is_available())

		return -ENODEV;



	return set_secvar_ops(&plpks_secvar_ops);

}

machine_device_initcall(pseries, plpks_secvar_init);