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[PATCH 0/7] ima: carry the measurement list across kexec

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  [PATCH 0/7] ima: carry the measurement list across kexec  Mimi Zohar <zohar@linux.vnet.ibm.com> - 2016-08-04 16:10 +0200
    [PATCH 3/7] ima: maintain memory size needed for serializing the measurement list Mimi Zohar <zohar@linux.vnet.ibm.com> - 2016-08-04 16:40 +0200
    [PATCH 4/7] ima: serialize the binary_runtime_measurements Mimi Zohar <zohar@linux.vnet.ibm.com> - 2016-08-04 17:10 +0200
    [PATCH 6/7] ima: store the builtin/custom template definitions in a list Mimi Zohar <zohar@linux.vnet.ibm.com> - 2016-08-04 17:40 +0200
    [PATCH 7/7] ima: support restoring multiple template formats Mimi Zohar <zohar@linux.vnet.ibm.com> - 2016-08-04 17:40 +0200
    Re: [PATCH 0/7] ima: carry the measurement list across kexec Balbir Singh <bsingharora@gmail.com> - 2016-08-09 07:20 +0200
      Re: [PATCH 0/7] ima: carry the measurement list across kexec Mimi Zohar <zohar@linux.vnet.ibm.com> - 2016-08-09 14:40 +0200

#1456419 — [PATCH 0/7] ima: carry the measurement list across kexec

The TPM PCRs are only reset on a hard reboot.  In order to validate a
TPM's quote after a soft reboot (eg. kexec -e), the IMA measurement list
of the running kernel must be saved and then restored on the subsequent
boot.

The existing securityfs binary_runtime_measurements file conveniently
provides a serialized format of the IMA measurement list. This patch
set serializes the measurement list in this format and restores it.

This patch set pre-req's Thiago Bauermann's "kexec_file: Add buffer
hand-over for the next kernel" patch set* for actually carrying the
serialized measurement list across the kexec.

Mimi

*https://lists.infradead.org/pipermail/kexec/2016-June/016157.html

Mimi Zohar (6):
  ima: on soft reboot, restore the measurement list
  ima: permit duplicate measurement list entries
  ima: maintain memory size needed for serializing the measurement list
  ima: serialize the binary_runtime_measurements
  ima: store the builtin/custom template definitions in a list
  ima: support restoring multiple template formats

Thiago Jung Bauermann (1):
  ima: on soft reboot, save the measurement list

 include/linux/ima.h                   |  15 ++
 kernel/kexec_file.c                   |   3 +
 security/integrity/ima/Kconfig        |  12 ++
 security/integrity/ima/Makefile       |   1 +
 security/integrity/ima/ima.h          |  14 ++
 security/integrity/ima/ima_fs.c       |   2 +-
 security/integrity/ima/ima_init.c     |   2 +
 security/integrity/ima/ima_kexec.c    | 189 ++++++++++++++++++++++++
 security/integrity/ima/ima_main.c     |   1 +
 security/integrity/ima/ima_queue.c    |  72 +++++++++-
 security/integrity/ima/ima_template.c | 262 ++++++++++++++++++++++++++++++++--
 11 files changed, 556 insertions(+), 17 deletions(-)
 create mode 100644 security/integrity/ima/ima_kexec.c

-- 
2.1.0

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#1456436 — [PATCH 3/7] ima: maintain memory size needed for serializing the measurement list

In preparation for serializing the binary_runtime_measurements, this patch
maintains the amount of memory required.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
---
 security/integrity/ima/Kconfig     | 12 ++++++++++
 security/integrity/ima/ima.h       |  1 +
 security/integrity/ima/ima_queue.c | 49 ++++++++++++++++++++++++++++++++++++--
 3 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 0fb54d3..d764027 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -27,6 +27,18 @@ config IMA
 	  to learn more about IMA.
 	  If unsure, say N.
 
+config IMA_KEXEC
+	bool "Enable carrying the IMA measurement list across a soft boot"
+	depends on IMA && TCG_TPM && KEXEC_FILE
+	default n
+	help
+	   TPM PCRs are only reset on a hard reboot.  In order to validate
+	   a TPM's quote after a soft boot, the IMA measurement list of the
+	   running kernel must be saved and restored on boot.
+
+	   Depending on the IMA policy, the measurement list can grow to
+	   be very large.
+
 config IMA_MEASURE_PCR_IDX
 	int
 	depends on IMA
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 84e8d36..222668f 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -132,6 +132,7 @@ struct ima_template_desc *ima_template_desc_current(void);
 void ima_load_kexec_buffer(void);
 int ima_restore_measurement_entry(struct ima_template_entry *entry);
 int ima_restore_measurement_list(loff_t bufsize, void *buf);
+unsigned long ima_get_binary_runtime_size(void);
 int ima_init_template(void);
 
 /*
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 12d1b04..8f0661b 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -29,6 +29,11 @@
 #define AUDIT_CAUSE_LEN_MAX 32
 
 LIST_HEAD(ima_measurements);	/* list of all measurements */
+#ifdef CONFIG_IMA_KEXEC
+static unsigned long binary_runtime_size;
+#else
+static unsigned long binary_runtime_size = ULONG_MAX;
+#endif
 
 /* key: inode (before secure-hashing a file) */
 struct ima_h_table ima_htable = {
@@ -64,6 +69,24 @@ static struct ima_queue_entry *ima_lookup_digest_entry(u8 *digest_value,
 	return ret;
 }
 
+/*
+ * Calculate the memory required for serializing a single
+ * binary_runtime_measurement list entry, which contains a
+ * couple of variable length fields (e.g template name and data).
+ */
+static int get_binary_runtime_size(struct ima_template_entry *entry)
+{
+	int size = 0;
+
+	size += sizeof(u32);	/* pcr */
+	size += sizeof(entry->digest);
+	size += sizeof(int);	/* template name size field */
+	size += strlen(entry->template_desc->name);
+	size += sizeof(entry->template_data_len);
+	size += entry->template_data_len;
+	return size;
+}
+
 /* ima_add_template_entry helper function:
  * - Add template entry to the measurement list and hash table, for
  *   all entries except those carried across kexec.
@@ -90,9 +113,26 @@ static int ima_add_digest_entry(struct ima_template_entry *entry, int flags)
 		key = ima_hash_key(entry->digest);
 		hlist_add_head_rcu(&qe->hnext, &ima_htable.queue[key]);
 	}
+
+	if (binary_runtime_size != ULONG_MAX) {
+		int size;
+
+		size = get_binary_runtime_size(entry);
+		binary_runtime_size = (binary_runtime_size < ULONG_MAX - size) ?
+		     binary_runtime_size + size : ULONG_MAX;
+	}
 	return 0;
 }
 
+/*
+ * Return the amount of memory required for serializing the
+ * entire binary_runtime_measurement list.
+ */
+unsigned long ima_get_binary_runtime_size(void)
+{
+	return binary_runtime_size;
+};
+
 static int ima_pcr_extend(const u8 *hash, int pcr)
 {
 	int result = 0;
@@ -106,8 +146,13 @@ static int ima_pcr_extend(const u8 *hash, int pcr)
 	return result;
 }
 
-/* Add template entry to the measurement list and hash table,
- * and extend the pcr.
+/*
+ * Add template entry to the measurement list and hash table, and
+ * extend the pcr.
+ *
+ * On systems which support carrying the IMA measurement list across
+ * kexec, maintain the total memory size required for serializing the
+ * binary_runtime_measurements.
  */
 int ima_add_template_entry(struct ima_template_entry *entry, int violation,
 			   const char *op, struct inode *inode,
-- 
2.1.0

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#1456476 — [PATCH 4/7] ima: serialize the binary_runtime_measurements

The TPM PCRs are only reset on a hard reboot.  In order to validate a
TPM's quote after a soft reboot (eg. kexec -e), the IMA measurement list
of the running kernel must be saved and restored on boot.  This patch
serializes the IMA measurement list in the binary_runtime_measurements
format.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
---
 security/integrity/ima/ima.h       |  1 +
 security/integrity/ima/ima_fs.c    |  2 +-
 security/integrity/ima/ima_kexec.c | 51 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 222668f..f972296 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -132,6 +132,7 @@ struct ima_template_desc *ima_template_desc_current(void);
 void ima_load_kexec_buffer(void);
 int ima_restore_measurement_entry(struct ima_template_entry *entry);
 int ima_restore_measurement_list(loff_t bufsize, void *buf);
+int ima_measurements_show(struct seq_file *m, void *v);
 unsigned long ima_get_binary_runtime_size(void);
 int ima_init_template(void);
 
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index c07a384..66e5dd5 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -116,7 +116,7 @@ void ima_putc(struct seq_file *m, void *data, int datalen)
  *       [eventdata length]
  *       eventdata[n]=template specific data
  */
-static int ima_measurements_show(struct seq_file *m, void *v)
+int ima_measurements_show(struct seq_file *m, void *v)
 {
 	/* the list never shrinks, so we don't need a lock here */
 	struct ima_queue_entry *qe = v;
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 6a046ad..e77ca9d 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -23,6 +23,57 @@
 
 #include "ima.h"
 
+static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
+				     unsigned long segment_size)
+{
+	struct ima_queue_entry *qe;
+	struct seq_file file;
+	struct ima_kexec_hdr khdr = {
+		.version = 1, .buffer_size = 0, .count = 0};
+	int ret = 0;
+
+	/* segment size can't change between kexec load and execute */
+	file.buf = vmalloc(segment_size);
+	if (!file.buf) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	file.size = segment_size;
+	file.read_pos = 0;
+	file.count = sizeof(khdr);	/* reserved space */
+
+	list_for_each_entry_rcu(qe, &ima_measurements, later) {
+		if (file.count < file.size) {
+			khdr.count++;
+			ima_measurements_show(&file, qe);
+		} else {
+			ret = -EINVAL;
+			break;
+		}
+	}
+
+	if (ret < 0)
+		goto out;
+
+	/*
+	 * fill in reserved space with some buffer details
+	 * (eg. version, buffer size, number of measurements)
+	 */
+	khdr.buffer_size = file.count;
+	memcpy(file.buf, &khdr, sizeof(khdr));
+	print_hex_dump(KERN_DEBUG, "ima dump: ", DUMP_PREFIX_NONE,
+			16, 1, file.buf,
+			file.count < 100 ? file.count : 100, true);
+
+	*buffer_size = file.count;
+	*buffer = file.buf;
+out:
+	if (ret == -EINVAL)
+		vfree(file.buf);
+	return ret;
+}
+
 /*
  * Restore the measurement list from the previous kernel.
  */
-- 
2.1.0

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#1456487 — [PATCH 6/7] ima: store the builtin/custom template definitions in a list

The builtin and single custom templates are currently stored in an
array.  In preparation for being able to restore a measurement list
containing multiple builtin/custom templates, this patch stores the
builtin and custom templates as a linked list.  This will permit
defining more than one custom template per boot.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
---
 security/integrity/ima/ima.h          |  2 ++
 security/integrity/ima/ima_main.c     |  1 +
 security/integrity/ima/ima_template.c | 37 +++++++++++++++++++++++++++--------
 3 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index f972296..9d7fdd5 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -81,6 +81,7 @@ struct ima_template_field {
 
 /* IMA template descriptor definition */
 struct ima_template_desc {
+	struct list_head list;
 	char *name;
 	char *fmt;
 	int num_fields;
@@ -135,6 +136,7 @@ int ima_restore_measurement_list(loff_t bufsize, void *buf);
 int ima_measurements_show(struct seq_file *m, void *v);
 unsigned long ima_get_binary_runtime_size(void);
 int ima_init_template(void);
+void ima_init_template_list(void);
 
 /*
  * used to protect h_table and sha_table
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 596ef61..592f318 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -418,6 +418,7 @@ static int __init init_ima(void)
 {
 	int error;
 
+	ima_init_template_list();
 	hash_setup(CONFIG_IMA_DEFAULT_HASH);
 	error = ima_init();
 	if (!error) {
diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
index c6510f0..b7bcb62 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c
@@ -15,16 +15,20 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/rculist.h>
 #include "ima.h"
 #include "ima_template_lib.h"
 
-static struct ima_template_desc defined_templates[] = {
+static struct ima_template_desc builtin_templates[] = {
 	{.name = IMA_TEMPLATE_IMA_NAME, .fmt = IMA_TEMPLATE_IMA_FMT},
 	{.name = "ima-ng", .fmt = "d-ng|n-ng"},
 	{.name = "ima-sig", .fmt = "d-ng|n-ng|sig"},
 	{.name = "", .fmt = ""},	/* placeholder for a custom format */
 };
 
+static LIST_HEAD(defined_templates);
+spinlock_t template_list;
+
 static struct ima_template_field supported_fields[] = {
 	{.field_id = "d", .field_init = ima_eventdigest_init,
 	 .field_show = ima_show_template_digest},
@@ -80,7 +84,7 @@ __setup("ima_template=", ima_template_setup);
 
 static int __init ima_template_fmt_setup(char *str)
 {
-	int num_templates = ARRAY_SIZE(defined_templates);
+	int num_templates = ARRAY_SIZE(builtin_templates);
 
 	if (ima_template)
 		return 1;
@@ -91,20 +95,24 @@ static int __init ima_template_fmt_setup(char *str)
 		return 1;
 	}
 
-	defined_templates[num_templates - 1].fmt = str;
-	ima_template = defined_templates + num_templates - 1;
+	builtin_templates[num_templates - 1].fmt = str;
+	ima_template = builtin_templates + num_templates - 1;
+
 	return 1;
 }
 __setup("ima_template_fmt=", ima_template_fmt_setup);
 
 static struct ima_template_desc *lookup_template_desc(const char *name)
 {
-	int i;
+	struct ima_template_desc *template_desc;
 
-	for (i = 0; i < ARRAY_SIZE(defined_templates); i++) {
-		if (strcmp(defined_templates[i].name, name) == 0)
-			return defined_templates + i;
+	rcu_read_lock();
+	list_for_each_entry_rcu(template_desc, &defined_templates, list) {
+		if ((strcmp(template_desc->name, name) == 0) ||
+		    (strcmp(template_desc->fmt, name) == 0))
+			return template_desc;
 	}
+	rcu_read_unlock();
 
 	return NULL;
 }
@@ -190,6 +198,19 @@ struct ima_template_desc *ima_template_desc_current(void)
 	return ima_template;
 }
 
+void __init ima_init_template_list(void)
+{
+	int i;
+
+	spin_lock(&template_list);
+	for (i = 0; i < ARRAY_SIZE(builtin_templates); i++) {
+		list_add_tail_rcu(&builtin_templates[i].list,
+				  &defined_templates);
+	}
+	spin_unlock(&template_list);
+	synchronize_rcu();
+}
+
 int __init ima_init_template(void)
 {
 	struct ima_template_desc *template = ima_template_desc_current();
-- 
2.1.0

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#1456494 — [PATCH 7/7] ima: support restoring multiple template formats

The configured IMA measurement list template format can be replaced at
runtime on the boot command line, including a custom template format.
This patch adds support for restoring a measuremement list containing
multiple builtin/custom template formats.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
---
 security/integrity/ima/ima_template.c | 58 +++++++++++++++++++++++++++++++++--
 1 file changed, 55 insertions(+), 3 deletions(-)

diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
index b7bcb62..3923718 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c
@@ -56,6 +56,8 @@ static int __init ima_template_setup(char *str)
 	if (ima_template)
 		return 1;
 
+	ima_init_template_list();
+
 	/*
 	 * Verify that a template with the supplied name exists.
 	 * If not, use CONFIG_IMA_DEFAULT_TEMPLATE.
@@ -150,9 +152,14 @@ static int template_desc_init_fields(const char *template_fmt,
 {
 	const char *template_fmt_ptr;
 	struct ima_template_field *found_fields[IMA_TEMPLATE_NUM_FIELDS_MAX];
-	int template_num_fields = template_fmt_size(template_fmt);
+	int template_num_fields;
 	int i, len;
 
+	if (num_fields && *num_fields > 0) /* already initialized? */
+		return 0;
+
+	template_num_fields = template_fmt_size(template_fmt);
+
 	if (template_num_fields > IMA_TEMPLATE_NUM_FIELDS_MAX) {
 		pr_err("format string '%s' contains too many fields\n",
 		       template_fmt);
@@ -202,6 +209,9 @@ void __init ima_init_template_list(void)
 {
 	int i;
 
+	if (!list_empty(&defined_templates))
+		return;
+
 	spin_lock(&template_list);
 	for (i = 0; i < ARRAY_SIZE(builtin_templates); i++) {
 		list_add_tail_rcu(&builtin_templates[i].list,
@@ -227,6 +237,35 @@ int __init ima_init_template(void)
 	return result;
 }
 
+static struct ima_template_desc *restore_template_fmt(char *template_name)
+{
+	struct ima_template_desc *template_desc = NULL;
+	int ret;
+
+	ret = template_desc_init_fields(template_name, NULL, NULL);
+	if (ret < 0) {
+		pr_err("attempting to initialize the template \"%s\" failed\n",
+			template_name);
+		goto out;
+	}
+
+	template_desc = kzalloc(sizeof(*template_desc), GFP_KERNEL);
+	if (!template_desc)
+		goto out;
+
+	template_desc->name = "";
+	template_desc->fmt = kstrdup(template_name, GFP_KERNEL);
+	if (!template_desc->fmt)
+		goto out;
+
+	spin_lock(&template_list);
+	list_add_tail_rcu(&template_desc->list, &defined_templates);
+	spin_unlock(&template_list);
+	synchronize_rcu();
+out:
+	return template_desc;
+}
+
 static int ima_restore_template_data(struct ima_template_desc *template_desc,
 				     void *template_data,
 				     int template_data_size,
@@ -359,10 +398,23 @@ int ima_restore_measurement_list(loff_t size, void *buf)
 		}
 		data_v1 = bufp += (u_int8_t)hdr_v1->template_name_len;
 
-		/* get template format */
 		template_desc = lookup_template_desc(template_name);
 		if (!template_desc) {
-			pr_err("template \"%s\" not found\n", template_name);
+			template_desc = restore_template_fmt(template_name);
+			if (!template_desc)
+				break;
+		}
+
+		/*
+		 * Only the running system's template format is initialized
+		 * on boot.  As needed, initialize the other template formats.
+		 */
+		ret = template_desc_init_fields(template_desc->fmt,
+						&(template_desc->fields),
+						&(template_desc->num_fields));
+		if (ret < 0) {
+			pr_err("attempting to restore the template fmt \"%s\" \
+				failed\n", template_desc->fmt);
 			ret = -EINVAL;
 			break;
 		}
-- 
2.1.0

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#1458405

On 04/08/16 22:24, Mimi Zohar wrote:
> The TPM PCRs are only reset on a hard reboot.  In order to validate a
> TPM's quote after a soft reboot (eg. kexec -e), the IMA measurement list
> of the running kernel must be saved and then restored on the subsequent
> boot.
> 
> The existing securityfs binary_runtime_measurements file conveniently
> provides a serialized format of the IMA measurement list. This patch
> set serializes the measurement list in this format and restores it.
> 
> This patch set pre-req's Thiago Bauermann's "kexec_file: Add buffer
> hand-over for the next kernel" patch set* for actually carrying the
> serialized measurement list across the kexec.
> 
> Mimi
> 

Hi, Mimi

I am trying to convince myself of the security of the solution. I asked
Thiago as well, but may be I am be lagging behind in understanding.

We trust the kernel to hand over PCR values of the old kernel (which
cannot be validated) to the IMA subsystem in the new kernel for storage.
I guess the idea is for ima_add_boot_aggregate to do the right thing?
How do we validate what the old kernel is giving us? Why do we care for
the old measurement list? Is it still of significance in the new kernel?


Balbir Singh.

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#1458687

On Tue, 2016-08-09 at 15:19 +1000, Balbir Singh wrote:
> 
> On 04/08/16 22:24, Mimi Zohar wrote:
> > The TPM PCRs are only reset on a hard reboot.  In order to validate a
> > TPM's quote after a soft reboot (eg. kexec -e), the IMA measurement list
> > of the running kernel must be saved and then restored on the subsequent
> > boot.
> > 
> > The existing securityfs binary_runtime_measurements file conveniently
> > provides a serialized format of the IMA measurement list. This patch
> > set serializes the measurement list in this format and restores it.
> > 
> > This patch set pre-req's Thiago Bauermann's "kexec_file: Add buffer
> > hand-over for the next kernel" patch set* for actually carrying the
> > serialized measurement list across the kexec.
> > 
> > Mimi
> > 
> 
> Hi, Mimi
> 
> I am trying to convince myself of the security of the solution. I asked
> Thiago as well, but may be I am be lagging behind in understanding.
> 
> We trust the kernel to hand over PCR values of the old kernel (which
> cannot be validated) to the IMA subsystem in the new kernel for storage.
> I guess the idea is for ima_add_boot_aggregate to do the right thing?
> How do we validate what the old kernel is giving us? Why do we care for
> the old measurement list? Is it still of significance in the new kernel?
> 

Hi Balbir,

To validate the hardware TPM PCR values requires walking the measurement
list simulating the TPM extend operation.  The resulting values should
match the hardware TPM PCRs.

In the case of a soft reboot, the TPM PCRs are not reset to 0, so all
the measurements of the running system, including those from previous
soft reboots, need to be included in the measurement list.   Without
these measurements, the simulated PCR values will not match the hardware
TPM PCR values.  Thus the need for this patch set.

Measurements can not be added/removed/changed in the measurement list
without it being detectable.

Mimi

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