[PATCH v4 00/13] ima: Introduce staging mechanism

[PATCH v4 00/13] ima: Introduce staging mechanism

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Introduction
============

The IMA measurements list is currently stored in the kernel memory. Memory
occupation grows linearly with the number of entries, and can become a
problem especially in environments with reduced resources.

While there is an advantage in keeping the IMA measurements list in kernel
memory, so that it is always available for reading from the securityfs
interfaces, storing it elsewhere would make it possible to free precious
memory for other kernel components.

Storing the IMA measurements list outside the kernel does not introduce
security issues, since its integrity is anyway protected by the TPM.

Hence, the new IMA staging mechanism is introduced to allow user space
to remove the desired portion of the measurements list from the kernel.

The IMA staging mechanism can be enabled from the kernel configuration with
the CONFIG_IMA_STAGING option.

If it is enabled, IMA duplicates the current measurements interfaces (both
binary and ASCII), by adding the ``_staged`` file suffix. Unlike the
existing counterparts, the ``_staged`` interfaces have write permission for
the root user and group, and require the process to have CAP_SYS_ADMIN set.

The staging mechanism supports two flavors.

Staging with prompt:

 1. ``echo A > <_staged interface>``: the user requests IMA to stage the
    entire measurements list;
 2. ``cat <_staged interface>``: the user reads the staged measurements;
 3. ``echo D > <_staged interface>`` : the user request IMA to delete
    staged measurements.

Staging and deleting:

 1. ``cat <_non_staged interface>``: the user reads the current
    measurements list and determines what the value N for staging should
    be;
 2. ``echo N > <_staged interface>``: the user requests IMA to delete N
    measurements from the current measurements list.

Since with the staging mechanism measurements entries are removed from the
kernel, the user needs to save the staged ones in a storage and concatenate
them together, so that it can present them to remote attestation agents as
if staging was never done.


Patch set content
=================

Patches 1-8 are preparatory patches to quickly replace the hash table,
maintain separate counters for the different measurements list types,
mediate access to the measurements list interface, and simplify the staging
patches.

Patch 9 introduces the staging with prompt flavor. Patch 10 makes it
possible to flush the hash table when deleting all the staged measurements.
Patch 11 introduces the staging and deleting flavor. Patch 12 avoids staged
measurements entries to be stored twice if there is contention between the
measurements interfaces and kexec. Patch 13 adds the documentation of the
staging mechanism.


Changelog
=========

v3:
 - Add Kconfig option to enable the staging mechanism (suggested by Mimi)
 - Change the meaning of BINARY_STAGED to be just the staged measurements
 - Separate the two staging flavors in two different functions:
   ima_queue_staged_delete_all() for staging with prompt,
   ima_queue_staged_delete_partial() for staging and deleting
 - Delete N entries without staging first (suggested by Mimi)
 - Avoid duplicate staged entries if there is contention between the
   measurements list interfaces and kexec

v2:
 - New patch to move measurements and violation counters outside the
   ima_h_table structure
 - New patch to quickly replace the hash table
 - Forbid partial deletion when flushing hash table (suggested by Mimi)
 - Ignore ima_flush_htable if CONFIG_IMA_DISABLE_HTABLE is enabled
 - BINARY_SIZE_* renamed to BINARY_* for better clarity
 - Removed ima_measurements_staged_exist and testing list empty instead
 - ima_queue_stage_trim() and ima_queue_delete_staged_trimmed() renamed to
   ima_queue_stage() and ima_queue_delete_staged()
 - New delete interval [1, ULONG_MAX - 1]
 - Rename ima_measure_lock to ima_measure_mutex
 - Move seq_open() and seq_release() outside the ima_measure_mutex lock
 - Drop ima_measurements_staged_read() and use seq_read() instead
 - Optimize create_securityfs_measurement_lists() changes
 - New file name format with _staged suffix at the end of the file name
 - Use _rcu list variant in ima_dump_measurement_list()
 - Remove support for direct trimming and splice the remaining entries to
   the active list (suggested by Mimi)
 - Hot swap the hash table if flushing is requested

v1:
 - Support for direct trimming without staging
 - Support unstaging on kexec (requested by Gregory Lumen)

Roberto Sassu (13):
  ima: Remove ima_h_table structure
  ima: Replace static htable queue with dynamically allocated array
  ima: Introduce per binary measurements list type ima_num_entries
    counter
  ima: Introduce per binary measurements list type binary_runtime_size
    value
  ima: Introduce _ima_measurements_start() and _ima_measurements_next()
  ima: Mediate open/release method of the measurements list
  ima: Use snprintf() in create_securityfs_measurement_lists
  ima: Introduce ima_dump_measurement()
  ima: Add support for staging measurements with prompt
  ima: Add support for flushing the hash table when staging measurements
  ima: Support staging and deleting N measurements entries
  ima: Return error on deleting staged measurements after kexec
  doc: security: Add documentation of the IMA staging mechanism

 .../admin-guide/kernel-parameters.txt         |   4 +
 Documentation/security/IMA-staging.rst        | 159 +++++++++
 Documentation/security/index.rst              |   1 +
 MAINTAINERS                                   |   2 +
 security/integrity/ima/Kconfig                |  16 +
 security/integrity/ima/ima.h                  |  28 +-
 security/integrity/ima/ima_api.c              |   2 +-
 security/integrity/ima/ima_fs.c               | 302 +++++++++++++++--
 security/integrity/ima/ima_init.c             |   5 +
 security/integrity/ima/ima_kexec.c            |  47 ++-
 security/integrity/ima/ima_queue.c            | 310 ++++++++++++++++--
 11 files changed, 803 insertions(+), 73 deletions(-)
 create mode 100644 Documentation/security/IMA-staging.rst

-- 
2.43.0

[PATCH v4 01/13] ima: Remove ima_h_table structure

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

With the upcoming change of dynamically allocating and replacing the hash
table, the ima_h_table structure would have been replaced with a new one.

However, since the ima_h_table structure contains also the counters for
number of measurements entries and violations, we would have needed to
preserve their values in the new ima_h_table structure.

Instead, separate those counters from the hash table, remove the
ima_h_table structure, and just replace the hash table pointer.

Finally, rename ima_show_htable_value(), ima_show_htable_violations()
and ima_htable_violations_ops respectively to ima_show_counter(),
ima_show_num_violations() and ima_num_violations_ops.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/ima.h       |  9 +++------
 security/integrity/ima/ima_api.c   |  2 +-
 security/integrity/ima/ima_fs.c    | 19 +++++++++----------
 security/integrity/ima/ima_kexec.c |  2 +-
 security/integrity/ima/ima_queue.c | 17 ++++++++++-------
 5 files changed, 24 insertions(+), 25 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 0eea02ff04df..d759988fde45 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -323,12 +323,9 @@ int ima_lsm_policy_change(struct notifier_block *nb, unsigned long event,
  */
 extern spinlock_t ima_queue_lock;
 
-struct ima_h_table {
-	atomic_long_t len;	/* number of stored measurements in the list */
-	atomic_long_t violations;
-	struct hlist_head queue[IMA_MEASURE_HTABLE_SIZE];
-};
-extern struct ima_h_table ima_htable;
+extern atomic_long_t ima_num_entries;
+extern atomic_long_t ima_num_violations;
+extern struct hlist_head ima_htable[IMA_MEASURE_HTABLE_SIZE];
 
 static inline unsigned int ima_hash_key(u8 *digest)
 {
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 0916f24f005f..122d127e108d 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -146,7 +146,7 @@ void ima_add_violation(struct file *file, const unsigned char *filename,
 	int result;
 
 	/* can overflow, only indicator */
-	atomic_long_inc(&ima_htable.violations);
+	atomic_long_inc(&ima_num_violations);
 
 	result = ima_alloc_init_template(&event_data, &entry, NULL);
 	if (result < 0) {
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index ca4931a95098..aaa460d70ff7 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -38,8 +38,8 @@ __setup("ima_canonical_fmt", default_canonical_fmt_setup);
 
 static int valid_policy = 1;
 
-static ssize_t ima_show_htable_value(char __user *buf, size_t count,
-				     loff_t *ppos, atomic_long_t *val)
+static ssize_t ima_show_counter(char __user *buf, size_t count, loff_t *ppos,
+				atomic_long_t *val)
 {
 	char tmpbuf[32];	/* greater than largest 'long' string value */
 	ssize_t len;
@@ -48,15 +48,14 @@ static ssize_t ima_show_htable_value(char __user *buf, size_t count,
 	return simple_read_from_buffer(buf, count, ppos, tmpbuf, len);
 }
 
-static ssize_t ima_show_htable_violations(struct file *filp,
-					  char __user *buf,
-					  size_t count, loff_t *ppos)
+static ssize_t ima_show_num_violations(struct file *filp, char __user *buf,
+				       size_t count, loff_t *ppos)
 {
-	return ima_show_htable_value(buf, count, ppos, &ima_htable.violations);
+	return ima_show_counter(buf, count, ppos, &ima_num_violations);
 }
 
-static const struct file_operations ima_htable_violations_ops = {
-	.read = ima_show_htable_violations,
+static const struct file_operations ima_num_violations_ops = {
+	.read = ima_show_num_violations,
 	.llseek = generic_file_llseek,
 };
 
@@ -64,7 +63,7 @@ static ssize_t ima_show_measurements_count(struct file *filp,
 					   char __user *buf,
 					   size_t count, loff_t *ppos)
 {
-	return ima_show_htable_value(buf, count, ppos, &ima_htable.len);
+	return ima_show_counter(buf, count, ppos, &ima_num_entries);
 
 }
 
@@ -545,7 +544,7 @@ int __init ima_fs_init(void)
 	}
 
 	dentry = securityfs_create_file("violations", S_IRUSR | S_IRGRP,
-				   ima_dir, NULL, &ima_htable_violations_ops);
+				   ima_dir, NULL, &ima_num_violations_ops);
 	if (IS_ERR(dentry)) {
 		ret = PTR_ERR(dentry);
 		goto out;
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 36a34c54de58..5801649fbbef 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -43,7 +43,7 @@ void ima_measure_kexec_event(const char *event_name)
 	int n;
 
 	buf_size = ima_get_binary_runtime_size();
-	len = atomic_long_read(&ima_htable.len);
+	len = atomic_long_read(&ima_num_entries);
 
 	n = scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
 		      "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;"
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 319522450854..1f6515f7d015 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -32,11 +32,14 @@ static unsigned long binary_runtime_size;
 static unsigned long binary_runtime_size = ULONG_MAX;
 #endif
 
+/* num of stored measurements in the list */
+atomic_long_t ima_num_entries = ATOMIC_LONG_INIT(0);
+/* num of violations in the list */
+atomic_long_t ima_num_violations = ATOMIC_LONG_INIT(0);
+
 /* key: inode (before secure-hashing a file) */
-struct ima_h_table ima_htable = {
-	.len = ATOMIC_LONG_INIT(0),
-	.violations = ATOMIC_LONG_INIT(0),
-	.queue[0 ... IMA_MEASURE_HTABLE_SIZE - 1] = HLIST_HEAD_INIT
+struct hlist_head ima_htable[IMA_MEASURE_HTABLE_SIZE] = {
+	[0 ... IMA_MEASURE_HTABLE_SIZE - 1] = HLIST_HEAD_INIT
 };
 
 /* mutex protects atomicity of extending measurement list
@@ -61,7 +64,7 @@ static struct ima_queue_entry *ima_lookup_digest_entry(u8 *digest_value,
 
 	key = ima_hash_key(digest_value);
 	rcu_read_lock();
-	hlist_for_each_entry_rcu(qe, &ima_htable.queue[key], hnext) {
+	hlist_for_each_entry_rcu(qe, &ima_htable[key], hnext) {
 		rc = memcmp(qe->entry->digests[ima_hash_algo_idx].digest,
 			    digest_value, hash_digest_size[ima_hash_algo]);
 		if ((rc == 0) && (qe->entry->pcr == pcr)) {
@@ -113,10 +116,10 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
 	INIT_LIST_HEAD(&qe->later);
 	list_add_tail_rcu(&qe->later, &ima_measurements);
 
-	atomic_long_inc(&ima_htable.len);
+	atomic_long_inc(&ima_num_entries);
 	if (update_htable) {
 		key = ima_hash_key(entry->digests[ima_hash_algo_idx].digest);
-		hlist_add_head_rcu(&qe->hnext, &ima_htable.queue[key]);
+		hlist_add_head_rcu(&qe->hnext, &ima_htable[key]);
 	}
 
 	if (binary_runtime_size != ULONG_MAX) {
-- 
2.43.0

[PATCH v4 02/13] ima: Replace static htable queue with dynamically allocated array

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

The IMA hash table is a fixed-size array of hlist_head buckets:

    struct hlist_head ima_htable[IMA_MEASURE_HTABLE_SIZE];

IMA_MEASURE_HTABLE_SIZE is (1 << IMA_HASH_BITS) = 1024 buckets, each a
struct hlist_head (one pointer, 8 bytes on 64-bit). That is 8 KiB allocated
in BSS for every kernel, regardless of whether IMA is ever used, and
regardless of how many measurements are actually made.

Replace the fixed-size array with a RCU-protected pointer to a dynamically
allocated array that is initialized in ima_init_htable(), which is called
from ima_init() during early boot. ima_init_htable() calls the static
function ima_alloc_replace_htable() which, other than initializing the hash
table the first time, can also hot-swap the existing hash table with a
blank one.

The allocation in ima_alloc_replace_htable() uses kcalloc() so the buckets
are zero-initialised (equivalent to HLIST_HEAD_INIT { .first = NULL }).
Callers of ima_alloc_replace_htable() must call synchronize_rcu() and free
the returned hash table.

Finally, access the hash table with rcu_dereference() in
ima_lookup_digest_entry() (reader side) and with
rcu_dereference_protected() in ima_add_digest_entry() (writer side).

No functional change: bucket count, hash function, and all locking remain
identical.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/ima.h       |  3 +-
 security/integrity/ima/ima_init.c  |  5 ++++
 security/integrity/ima/ima_queue.c | 48 ++++++++++++++++++++++++++----
 3 files changed, 50 insertions(+), 6 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index d759988fde45..9cdc4c5afd3b 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -310,6 +310,7 @@ bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
 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);
+int __init ima_init_htable(void);
 unsigned long ima_get_binary_runtime_size(void);
 int ima_init_template(void);
 void ima_init_template_list(void);
@@ -325,7 +326,7 @@ extern spinlock_t ima_queue_lock;
 
 extern atomic_long_t ima_num_entries;
 extern atomic_long_t ima_num_violations;
-extern struct hlist_head ima_htable[IMA_MEASURE_HTABLE_SIZE];
+extern struct hlist_head __rcu *ima_htable;
 
 static inline unsigned int ima_hash_key(u8 *digest)
 {
diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
index a2f34f2d8ad7..7e0aa09a12e6 100644
--- a/security/integrity/ima/ima_init.c
+++ b/security/integrity/ima/ima_init.c
@@ -140,6 +140,11 @@ int __init ima_init(void)
 	rc = ima_init_digests();
 	if (rc != 0)
 		return rc;
+
+	rc = ima_init_htable();
+	if (rc != 0)
+		return rc;
+
 	rc = ima_add_boot_aggregate();	/* boot aggregate must be first entry */
 	if (rc != 0)
 		return rc;
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 1f6515f7d015..41f4941ceaad 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -38,9 +38,7 @@ atomic_long_t ima_num_entries = ATOMIC_LONG_INIT(0);
 atomic_long_t ima_num_violations = ATOMIC_LONG_INIT(0);
 
 /* key: inode (before secure-hashing a file) */
-struct hlist_head ima_htable[IMA_MEASURE_HTABLE_SIZE] = {
-	[0 ... IMA_MEASURE_HTABLE_SIZE - 1] = HLIST_HEAD_INIT
-};
+struct hlist_head __rcu *ima_htable;
 
 /* mutex protects atomicity of extending measurement list
  * and extending the TPM PCR aggregate. Since tpm_extend can take
@@ -54,17 +52,53 @@ static DEFINE_MUTEX(ima_extend_list_mutex);
  */
 static bool ima_measurements_suspended;
 
+/* Callers must call synchronize_rcu() and free the hash table. */
+static struct hlist_head *ima_alloc_replace_htable(void)
+{
+	struct hlist_head *old_htable, *new_htable;
+
+	/* Initializing to zeros is equivalent to call HLIST_HEAD_INIT. */
+	new_htable = kcalloc(IMA_MEASURE_HTABLE_SIZE, sizeof(struct hlist_head),
+			     GFP_KERNEL);
+	if (!new_htable)
+		return ERR_PTR(-ENOMEM);
+
+	old_htable = rcu_replace_pointer(ima_htable, new_htable,
+				lockdep_is_held(&ima_extend_list_mutex));
+
+	return old_htable;
+}
+
+int __init ima_init_htable(void)
+{
+	struct hlist_head *old_htable;
+
+	mutex_lock(&ima_extend_list_mutex);
+	old_htable = ima_alloc_replace_htable();
+	mutex_unlock(&ima_extend_list_mutex);
+
+	if (IS_ERR(old_htable))
+		return PTR_ERR(old_htable);
+
+	/* Synchronize_rcu() and kfree() not necessary, only for robustness. */
+	synchronize_rcu();
+	kfree(old_htable);
+	return 0;
+}
+
 /* lookup up the digest value in the hash table, and return the entry */
 static struct ima_queue_entry *ima_lookup_digest_entry(u8 *digest_value,
 						       int pcr)
 {
 	struct ima_queue_entry *qe, *ret = NULL;
+	struct hlist_head *htable;
 	unsigned int key;
 	int rc;
 
 	key = ima_hash_key(digest_value);
 	rcu_read_lock();
-	hlist_for_each_entry_rcu(qe, &ima_htable[key], hnext) {
+	htable = rcu_dereference(ima_htable);
+	hlist_for_each_entry_rcu(qe, &htable[key], hnext) {
 		rc = memcmp(qe->entry->digests[ima_hash_algo_idx].digest,
 			    digest_value, hash_digest_size[ima_hash_algo]);
 		if ((rc == 0) && (qe->entry->pcr == pcr)) {
@@ -104,6 +138,7 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
 				bool update_htable)
 {
 	struct ima_queue_entry *qe;
+	struct hlist_head *htable;
 	unsigned int key;
 
 	qe = kmalloc_obj(*qe);
@@ -116,10 +151,13 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
 	INIT_LIST_HEAD(&qe->later);
 	list_add_tail_rcu(&qe->later, &ima_measurements);
 
+	htable = rcu_dereference_protected(ima_htable,
+				lockdep_is_held(&ima_extend_list_mutex));
+
 	atomic_long_inc(&ima_num_entries);
 	if (update_htable) {
 		key = ima_hash_key(entry->digests[ima_hash_algo_idx].digest);
-		hlist_add_head_rcu(&qe->hnext, &ima_htable[key]);
+		hlist_add_head_rcu(&qe->hnext, &htable[key]);
 	}
 
 	if (binary_runtime_size != ULONG_MAX) {
-- 
2.43.0

[PATCH v4 03/13] ima: Introduce per binary measurements list type ima_num_entries counter

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Make ima_num_entries as an array, to have separate counters per binary
measurements list type. Currently, define the BINARY type for the existing
binary measurements list.

No functional change: the BINARY type is equivalent to the value without
the array.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/ima.h       | 9 ++++++++-
 security/integrity/ima/ima_fs.c    | 3 +--
 security/integrity/ima/ima_kexec.c | 2 +-
 security/integrity/ima/ima_queue.c | 7 +++++--
 4 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 9cdc4c5afd3b..199237e2d2e3 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -28,6 +28,13 @@ enum ima_show_type { IMA_SHOW_BINARY, IMA_SHOW_BINARY_NO_FIELD_LEN,
 		     IMA_SHOW_BINARY_OLD_STRING_FMT, IMA_SHOW_ASCII };
 enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8, TPM_PCR10 = 10 };
 
+/*
+ * BINARY: current binary measurements list
+ */
+enum binary_lists {
+	BINARY, BINARY__LAST
+};
+
 /* digest size for IMA, fits SHA1 or MD5 */
 #define IMA_DIGEST_SIZE		SHA1_DIGEST_SIZE
 #define IMA_EVENT_NAME_LEN_MAX	255
@@ -324,7 +331,7 @@ int ima_lsm_policy_change(struct notifier_block *nb, unsigned long event,
  */
 extern spinlock_t ima_queue_lock;
 
-extern atomic_long_t ima_num_entries;
+extern atomic_long_t ima_num_entries[BINARY__LAST];
 extern atomic_long_t ima_num_violations;
 extern struct hlist_head __rcu *ima_htable;
 
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index aaa460d70ff7..79b0f287c668 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -63,8 +63,7 @@ static ssize_t ima_show_measurements_count(struct file *filp,
 					   char __user *buf,
 					   size_t count, loff_t *ppos)
 {
-	return ima_show_counter(buf, count, ppos, &ima_num_entries);
-
+	return ima_show_counter(buf, count, ppos, &ima_num_entries[BINARY]);
 }
 
 static const struct file_operations ima_measurements_count_ops = {
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 5801649fbbef..40962dc0ca86 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -43,7 +43,7 @@ void ima_measure_kexec_event(const char *event_name)
 	int n;
 
 	buf_size = ima_get_binary_runtime_size();
-	len = atomic_long_read(&ima_num_entries);
+	len = atomic_long_read(&ima_num_entries[BINARY]);
 
 	n = scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
 		      "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;"
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 41f4941ceaad..952172a4905d 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -33,7 +33,10 @@ static unsigned long binary_runtime_size = ULONG_MAX;
 #endif
 
 /* num of stored measurements in the list */
-atomic_long_t ima_num_entries = ATOMIC_LONG_INIT(0);
+atomic_long_t ima_num_entries[BINARY__LAST] = {
+	[0 ... BINARY__LAST - 1] = ATOMIC_LONG_INIT(0)
+};
+
 /* num of violations in the list */
 atomic_long_t ima_num_violations = ATOMIC_LONG_INIT(0);
 
@@ -154,7 +157,7 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
 	htable = rcu_dereference_protected(ima_htable,
 				lockdep_is_held(&ima_extend_list_mutex));
 
-	atomic_long_inc(&ima_num_entries);
+	atomic_long_inc(&ima_num_entries[BINARY]);
 	if (update_htable) {
 		key = ima_hash_key(entry->digests[ima_hash_algo_idx].digest);
 		hlist_add_head_rcu(&qe->hnext, &htable[key]);
-- 
2.43.0

[PATCH v4 04/13] ima: Introduce per binary measurements list type binary_runtime_size value

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Make binary_runtime_size as an array, to have separate counters per binary
measurements list type. Currently, define the BINARY type for the existing
binary measurements list.

Introduce ima_update_binary_runtime_size() to facilitate updating a
binary_runtime_size value with a given binary measurement list type.

Also add the binary measurements list type parameter to
ima_get_binary_runtime_size(), to retrieve the desired value. Retrieving
the value is now done under the ima_extend_list_mutex, since there can be
concurrent updates.

No functional change (except for the mutex usage, that fixes the
concurrency issue): the BINARY array element is equivalent to the old
binary_runtime_size.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/ima.h       |  2 +-
 security/integrity/ima/ima_kexec.c |  5 ++--
 security/integrity/ima/ima_queue.c | 40 +++++++++++++++++++++---------
 3 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 199237e2d2e3..97b7d6024b5d 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -318,7 +318,7 @@ 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);
 int __init ima_init_htable(void);
-unsigned long ima_get_binary_runtime_size(void);
+unsigned long ima_get_binary_runtime_size(enum binary_lists binary_list);
 int ima_init_template(void);
 void ima_init_template_list(void);
 int __init ima_init_digests(void);
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 40962dc0ca86..44ebefbdcab0 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -42,7 +42,7 @@ void ima_measure_kexec_event(const char *event_name)
 	long len;
 	int n;
 
-	buf_size = ima_get_binary_runtime_size();
+	buf_size = ima_get_binary_runtime_size(BINARY);
 	len = atomic_long_read(&ima_num_entries[BINARY]);
 
 	n = scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
@@ -159,7 +159,8 @@ void ima_add_kexec_buffer(struct kimage *image)
 	else
 		extra_memory = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;
 
-	binary_runtime_size = ima_get_binary_runtime_size() + extra_memory;
+	binary_runtime_size = ima_get_binary_runtime_size(BINARY) +
+			      extra_memory;
 
 	if (binary_runtime_size >= ULONG_MAX - PAGE_SIZE)
 		kexec_segment_size = ULONG_MAX;
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 952172a4905d..b6d10dceb669 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -27,9 +27,11 @@ static struct tpm_digest *digests;
 
 LIST_HEAD(ima_measurements);	/* list of all measurements */
 #ifdef CONFIG_IMA_KEXEC
-static unsigned long binary_runtime_size;
+static unsigned long binary_runtime_size[BINARY__LAST];
 #else
-static unsigned long binary_runtime_size = ULONG_MAX;
+static unsigned long binary_runtime_size[BINARY__LAST] = {
+	[0 ... BINARY__LAST - 1] = ULONG_MAX
+};
 #endif
 
 /* num of stored measurements in the list */
@@ -131,6 +133,20 @@ static int get_binary_runtime_size(struct ima_template_entry *entry)
 	return size;
 }
 
+static void ima_update_binary_runtime_size(struct ima_template_entry *entry,
+					   enum binary_lists binary_list)
+{
+	int size;
+
+	if (binary_runtime_size[binary_list] == ULONG_MAX)
+		return;
+
+	size = get_binary_runtime_size(entry);
+	binary_runtime_size[binary_list] =
+		(binary_runtime_size[binary_list] < ULONG_MAX - size) ?
+		binary_runtime_size[binary_list] + size : ULONG_MAX;
+}
+
 /* ima_add_template_entry helper function:
  * - Add template entry to the measurement list and hash table, for
  *   all entries except those carried across kexec.
@@ -163,13 +179,7 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
 		hlist_add_head_rcu(&qe->hnext, &htable[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;
-	}
+	ima_update_binary_runtime_size(entry, BINARY);
 	return 0;
 }
 
@@ -178,12 +188,18 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
  * entire binary_runtime_measurement list, including the ima_kexec_hdr
  * structure.
  */
-unsigned long ima_get_binary_runtime_size(void)
+unsigned long ima_get_binary_runtime_size(enum binary_lists binary_list)
 {
-	if (binary_runtime_size >= (ULONG_MAX - sizeof(struct ima_kexec_hdr)))
+	unsigned long val;
+
+	mutex_lock(&ima_extend_list_mutex);
+	val = binary_runtime_size[binary_list];
+	mutex_unlock(&ima_extend_list_mutex);
+
+	if (val >= (ULONG_MAX - sizeof(struct ima_kexec_hdr)))
 		return ULONG_MAX;
 	else
-		return binary_runtime_size + sizeof(struct ima_kexec_hdr);
+		return val + sizeof(struct ima_kexec_hdr);
 }
 
 static int ima_pcr_extend(struct tpm_digest *digests_arg, int pcr)
-- 
2.43.0

[PATCH v4 05/13] ima: Introduce _ima_measurements_start() and _ima_measurements_next()

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Introduce _ima_measurements_start() and _ima_measurements_next(), renamed
from ima_measurements_start() and ima_measurements_next(), to include the
list head as an additional parameter, so that iteration on different lists
can be implemented by calling those functions.

No functional change: ima_measurements_start() and ima_measurements_next()
pass the ima_measurements list head, used before.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/ima_fs.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 79b0f287c668..9a8dba14d82a 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -72,14 +72,15 @@ static const struct file_operations ima_measurements_count_ops = {
 };
 
 /* returns pointer to hlist_node */
-static void *ima_measurements_start(struct seq_file *m, loff_t *pos)
+static void *_ima_measurements_start(struct seq_file *m, loff_t *pos,
+				     struct list_head *head)
 {
 	loff_t l = *pos;
 	struct ima_queue_entry *qe;
 
 	/* we need a lock since pos could point beyond last element */
 	rcu_read_lock();
-	list_for_each_entry_rcu(qe, &ima_measurements, later) {
+	list_for_each_entry_rcu(qe, head, later) {
 		if (!l--) {
 			rcu_read_unlock();
 			return qe;
@@ -89,7 +90,13 @@ static void *ima_measurements_start(struct seq_file *m, loff_t *pos)
 	return NULL;
 }
 
-static void *ima_measurements_next(struct seq_file *m, void *v, loff_t *pos)
+static void *ima_measurements_start(struct seq_file *m, loff_t *pos)
+{
+	return _ima_measurements_start(m, pos, &ima_measurements);
+}
+
+static void *_ima_measurements_next(struct seq_file *m, void *v, loff_t *pos,
+				    struct list_head *head)
 {
 	struct ima_queue_entry *qe = v;
 
@@ -101,7 +108,12 @@ static void *ima_measurements_next(struct seq_file *m, void *v, loff_t *pos)
 	rcu_read_unlock();
 	(*pos)++;
 
-	return (&qe->later == &ima_measurements) ? NULL : qe;
+	return (&qe->later == head) ? NULL : qe;
+}
+
+static void *ima_measurements_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	return _ima_measurements_next(m, v, pos, &ima_measurements);
 }
 
 static void ima_measurements_stop(struct seq_file *m, void *v)
-- 
2.43.0

[PATCH v4 06/13] ima: Mediate open/release method of the measurements list

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Introduce the ima_measure_users counter, to implement a semaphore-like
locking scheme where the binary and ASCII measurements list interfaces can
be concurrently open by multiple readers, or alternatively by a single
writer.

A semaphore cannot be used because the kernel cannot return to user space
with a lock held.

Introduce the ima_measure_lock() and ima_measure_unlock() primitives, to
respectively lock/unlock the interfaces (safely with the ima_measure_users
counter, without holding a lock).

Finally, introduce _ima_measurements_open() to lock the interface before
seq_open(), and call it from ima_measurements_open() and
ima_ascii_measurements_open(). And, introduce ima_measurements_release(),
to unlock the interface.

Require CAP_SYS_ADMIN if the interface is opened for write (not possible
for the current measurements interfaces, since they only have read
permission).

No functional changes: multiple readers are allowed as before.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/ima_fs.c | 71 +++++++++++++++++++++++++++++++--
 1 file changed, 67 insertions(+), 4 deletions(-)

diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 9a8dba14d82a..68edea7139d5 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -25,6 +25,8 @@
 #include "ima.h"
 
 static DEFINE_MUTEX(ima_write_mutex);
+static DEFINE_MUTEX(ima_measure_mutex);
+static long ima_measure_users;
 
 bool ima_canonical_fmt;
 static int __init default_canonical_fmt_setup(char *str)
@@ -209,16 +211,76 @@ static const struct seq_operations ima_measurments_seqops = {
 	.show = ima_measurements_show
 };
 
+static int ima_measure_lock(bool write)
+{
+	mutex_lock(&ima_measure_mutex);
+	if ((write && ima_measure_users != 0) ||
+	    (!write && ima_measure_users < 0)) {
+		mutex_unlock(&ima_measure_mutex);
+		return -EBUSY;
+	}
+
+	if (write)
+		ima_measure_users--;
+	else
+		ima_measure_users++;
+	mutex_unlock(&ima_measure_mutex);
+	return 0;
+}
+
+static void ima_measure_unlock(bool write)
+{
+	mutex_lock(&ima_measure_mutex);
+	if (write)
+		ima_measure_users++;
+	else
+		ima_measure_users--;
+	mutex_unlock(&ima_measure_mutex);
+}
+
+static int _ima_measurements_open(struct inode *inode, struct file *file,
+				  const struct seq_operations *seq_ops)
+{
+	bool write = (file->f_mode & FMODE_WRITE);
+	int ret;
+
+	if (write && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	ret = ima_measure_lock(write);
+	if (ret < 0)
+		return ret;
+
+	ret = seq_open(file, seq_ops);
+	if (ret < 0)
+		ima_measure_unlock(write);
+
+	return ret;
+}
+
 static int ima_measurements_open(struct inode *inode, struct file *file)
 {
-	return seq_open(file, &ima_measurments_seqops);
+	return _ima_measurements_open(inode, file, &ima_measurments_seqops);
+}
+
+static int ima_measurements_release(struct inode *inode, struct file *file)
+{
+	bool write = (file->f_mode & FMODE_WRITE);
+	int ret;
+
+	/* seq_release() always returns zero. */
+	ret = seq_release(inode, file);
+
+	ima_measure_unlock(write);
+
+	return ret;
 }
 
 static const struct file_operations ima_measurements_ops = {
 	.open = ima_measurements_open,
 	.read = seq_read,
 	.llseek = seq_lseek,
-	.release = seq_release,
+	.release = ima_measurements_release,
 };
 
 void ima_print_digest(struct seq_file *m, u8 *digest, u32 size)
@@ -283,14 +345,15 @@ static const struct seq_operations ima_ascii_measurements_seqops = {
 
 static int ima_ascii_measurements_open(struct inode *inode, struct file *file)
 {
-	return seq_open(file, &ima_ascii_measurements_seqops);
+	return _ima_measurements_open(inode, file,
+				      &ima_ascii_measurements_seqops);
 }
 
 static const struct file_operations ima_ascii_measurements_ops = {
 	.open = ima_ascii_measurements_open,
 	.read = seq_read,
 	.llseek = seq_lseek,
-	.release = seq_release,
+	.release = ima_measurements_release,
 };
 
 static ssize_t ima_read_policy(char *path)
-- 
2.43.0

[PATCH v4 07/13] ima: Use snprintf() in create_securityfs_measurement_lists

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Use the more secure snprintf() function (accepting the buffer size) in
create_securityfs_measurement_lists().

No functional change: sprintf() and snprintf() have the same behavior.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/ima_fs.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 68edea7139d5..7709a4576322 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -472,11 +472,13 @@ static int __init create_securityfs_measurement_lists(void)
 		struct dentry *dentry;
 
 		if (algo == HASH_ALGO__LAST)
-			sprintf(file_name, "ascii_runtime_measurements_tpm_alg_%x",
-				ima_tpm_chip->allocated_banks[i].alg_id);
+			snprintf(file_name, sizeof(file_name),
+				 "ascii_runtime_measurements_tpm_alg_%x",
+				 ima_tpm_chip->allocated_banks[i].alg_id);
 		else
-			sprintf(file_name, "ascii_runtime_measurements_%s",
-				hash_algo_name[algo]);
+			snprintf(file_name, sizeof(file_name),
+				 "ascii_runtime_measurements_%s",
+				 hash_algo_name[algo]);
 		dentry = securityfs_create_file(file_name, S_IRUSR | S_IRGRP,
 						ima_dir, (void *)(uintptr_t)i,
 						&ima_ascii_measurements_ops);
@@ -484,11 +486,13 @@ static int __init create_securityfs_measurement_lists(void)
 			return PTR_ERR(dentry);
 
 		if (algo == HASH_ALGO__LAST)
-			sprintf(file_name, "binary_runtime_measurements_tpm_alg_%x",
-				ima_tpm_chip->allocated_banks[i].alg_id);
+			snprintf(file_name, sizeof(file_name),
+				 "binary_runtime_measurements_tpm_alg_%x",
+				 ima_tpm_chip->allocated_banks[i].alg_id);
 		else
-			sprintf(file_name, "binary_runtime_measurements_%s",
-				hash_algo_name[algo]);
+			snprintf(file_name, sizeof(file_name),
+				 "binary_runtime_measurements_%s",
+				 hash_algo_name[algo]);
 		dentry = securityfs_create_file(file_name, S_IRUSR | S_IRGRP,
 						ima_dir, (void *)(uintptr_t)i,
 						&ima_measurements_ops);
-- 
2.43.0

[PATCH v4 08/13] ima: Introduce ima_dump_measurement()

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Introduce ima_dump_measurement() to simplify the code of
ima_dump_measurement_list() and to avoid repeating the
ima_dump_measurement() code block if iteration occurs on multiple lists.

No functional change: only code moved to a separate function.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/ima_kexec.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 44ebefbdcab0..d7d0fb639d99 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -80,6 +80,17 @@ static int ima_alloc_kexec_file_buf(size_t segment_size)
 	return 0;
 }
 
+static int ima_dump_measurement(struct ima_kexec_hdr *khdr,
+				struct ima_queue_entry *qe)
+{
+	if (ima_kexec_file.count >= ima_kexec_file.size)
+		return -EINVAL;
+
+	khdr->count++;
+	ima_measurements_show(&ima_kexec_file, qe);
+	return 0;
+}
+
 static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
 				     unsigned long segment_size)
 {
@@ -97,13 +108,9 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
 	khdr.version = 1;
 	/* This is an append-only list, no need to hold the RCU read lock */
 	list_for_each_entry_rcu(qe, &ima_measurements, later, true) {
-		if (ima_kexec_file.count < ima_kexec_file.size) {
-			khdr.count++;
-			ima_measurements_show(&ima_kexec_file, qe);
-		} else {
-			ret = -EINVAL;
+		ret = ima_dump_measurement(&khdr, qe);
+		if (ret < 0)
 			break;
-		}
 	}
 
 	/*
-- 
2.43.0

[PATCH v4 09/13] ima: Add support for staging measurements with prompt

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Introduce the ability of staging the IMA measurement list and deleting them
with a prompt.

Staging means moving the current content of the measurement list to a
separate location, and allowing users to read and delete it. This causes
the measurement list to be atomically truncated before new measurements can
be added. Staging can be done only once at a time. In the event of kexec(),
staging is reverted and staged entries will be carried over to the new
kernel.

Introduce ascii_runtime_measurements_<algo>_staged and
binary_runtime_measurements_<algo>_staged interfaces to stage and delete
the measurements. Use 'echo A > <IMA interface>' and
'echo D > <IMA interface>' to respectively stage and delete the entire
measurements list. Locking of these interfaces is also mediated with a call
to _ima_measurements_open() and with ima_measurements_release().

Implement the staging functionality by introducing the new global
measurements list ima_measurements_staged, and ima_queue_stage() and
ima_queue_delete_staged_all() to respectively move measurements from the
current measurements list to the staged one, and to move staged
measurements to the ima_measurements_trim list for deletion. Introduce
ima_queue_delete() to delete the measurements.

Finally, introduce the BINARY_STAGED AND BINARY_FULL binary measurements
list types, to maintain the counters and the binary size of staged
measurements and the full measurements list (including entries that were
staged). BINARY still represents the current binary measurements list.

Use the binary size for the BINARY + BINARY_STAGED types in
ima_add_kexec_buffer(), since both measurements list types are copied to
the secondary kernel during kexec. Use BINARY_FULL in
ima_measure_kexec_event(), to generate a critical data record.

It should be noted that the BINARY_FULL counter is not passed through
kexec. Thus, the number of entries included in the kexec critical data
records refers to the entries since the previous kexec records.

Note: This code derives from the Alt-IMA Huawei project, whose license is
      GPL-2.0 OR MIT.

Link: https://github.com/linux-integrity/linux/issues/1
Suggested-by: Gregory Lumen <gregorylumen@linux.microsoft.com> (staging revert)
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/Kconfig     |  13 +++
 security/integrity/ima/ima.h       |   8 +-
 security/integrity/ima/ima_fs.c    | 167 ++++++++++++++++++++++++++---
 security/integrity/ima/ima_kexec.c |  22 +++-
 security/integrity/ima/ima_queue.c |  97 ++++++++++++++++-
 5 files changed, 286 insertions(+), 21 deletions(-)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 976e75f9b9ba..e714726f3384 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -332,4 +332,17 @@ config IMA_KEXEC_EXTRA_MEMORY_KB
 	  If set to the default value of 0, an extra half page of memory for those
 	  additional measurements will be allocated.
 
+config IMA_STAGING
+	bool "Support for staging the measurements list"
+	default y
+	help
+	  Add support for staging the measurements list.
+
+	  It allows user space to stage the measurements list for deletion and
+	  to delete the staged measurements after confirmation.
+
+	  On kexec, staging is reverted and staged measurements are prepended
+	  to the current measurements list when measurements are copied to the
+	  secondary kernel.
+
 endif
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 97b7d6024b5d..65db152a0a24 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -30,9 +30,11 @@ enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8, TPM_PCR10 = 10 };
 
 /*
  * BINARY: current binary measurements list
+ * BINARY_STAGED: staged binary measurements list
+ * BINARY_FULL: binary measurements list since IMA init (lost after kexec)
  */
 enum binary_lists {
-	BINARY, BINARY__LAST
+	BINARY, BINARY_STAGED, BINARY_FULL, BINARY__LAST
 };
 
 /* digest size for IMA, fits SHA1 or MD5 */
@@ -125,6 +127,7 @@ struct ima_queue_entry {
 	struct ima_template_entry *entry;
 };
 extern struct list_head ima_measurements;	/* list of all measurements */
+extern struct list_head ima_measurements_staged; /* list of staged meas. */
 
 /* Some details preceding the binary serialized measurement list */
 struct ima_kexec_hdr {
@@ -314,6 +317,8 @@ struct ima_template_desc *ima_template_desc_current(void);
 struct ima_template_desc *ima_template_desc_buf(void);
 struct ima_template_desc *lookup_template_desc(const char *name);
 bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
+int ima_queue_stage(void);
+int ima_queue_staged_delete_all(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);
@@ -334,6 +339,7 @@ extern spinlock_t ima_queue_lock;
 extern atomic_long_t ima_num_entries[BINARY__LAST];
 extern atomic_long_t ima_num_violations;
 extern struct hlist_head __rcu *ima_htable;
+extern struct mutex ima_extend_list_mutex;
 
 static inline unsigned int ima_hash_key(u8 *digest)
 {
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 7709a4576322..39d9128e9f22 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -24,6 +24,13 @@
 
 #include "ima.h"
 
+/*
+ * Requests:
+ * 'A\n': stage the entire measurements list
+ * 'D\n': delete all staged measurements
+ */
+#define STAGED_REQ_LENGTH 21
+
 static DEFINE_MUTEX(ima_write_mutex);
 static DEFINE_MUTEX(ima_measure_mutex);
 static long ima_measure_users;
@@ -97,6 +104,11 @@ static void *ima_measurements_start(struct seq_file *m, loff_t *pos)
 	return _ima_measurements_start(m, pos, &ima_measurements);
 }
 
+static void *ima_measurements_staged_start(struct seq_file *m, loff_t *pos)
+{
+	return _ima_measurements_start(m, pos, &ima_measurements_staged);
+}
+
 static void *_ima_measurements_next(struct seq_file *m, void *v, loff_t *pos,
 				    struct list_head *head)
 {
@@ -118,6 +130,12 @@ static void *ima_measurements_next(struct seq_file *m, void *v, loff_t *pos)
 	return _ima_measurements_next(m, v, pos, &ima_measurements);
 }
 
+static void *ima_measurements_staged_next(struct seq_file *m, void *v,
+					  loff_t *pos)
+{
+	return _ima_measurements_next(m, v, pos, &ima_measurements_staged);
+}
+
 static void ima_measurements_stop(struct seq_file *m, void *v)
 {
 }
@@ -283,6 +301,68 @@ static const struct file_operations ima_measurements_ops = {
 	.release = ima_measurements_release,
 };
 
+static const struct seq_operations ima_measurments_staged_seqops = {
+	.start = ima_measurements_staged_start,
+	.next = ima_measurements_staged_next,
+	.stop = ima_measurements_stop,
+	.show = ima_measurements_show
+};
+
+static int ima_measurements_staged_open(struct inode *inode, struct file *file)
+{
+	return _ima_measurements_open(inode, file,
+				      &ima_measurments_staged_seqops);
+}
+
+static ssize_t ima_measurements_staged_write(struct file *file,
+					     const char __user *buf,
+					     size_t datalen, loff_t *ppos)
+{
+	char req[STAGED_REQ_LENGTH];
+	int ret;
+
+	if (*ppos > 0 || datalen < 2 || datalen > STAGED_REQ_LENGTH)
+		return -EINVAL;
+
+	if (copy_from_user(req, buf, datalen) != 0)
+		return -EFAULT;
+
+	if (req[datalen - 1] != '\n')
+		return -EINVAL;
+
+	req[datalen - 1] = '\0';
+
+	switch (req[0]) {
+	case 'A':
+		if (datalen != 2)
+			return -EINVAL;
+
+		ret = ima_queue_stage();
+		break;
+	case 'D':
+		if (datalen != 2)
+			return -EINVAL;
+
+		ret = ima_queue_staged_delete_all();
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	if (ret < 0)
+		return ret;
+
+	return datalen;
+}
+
+static const struct file_operations ima_measurements_staged_ops = {
+	.open = ima_measurements_staged_open,
+	.read = seq_read,
+	.write = ima_measurements_staged_write,
+	.llseek = seq_lseek,
+	.release = ima_measurements_release,
+};
+
 void ima_print_digest(struct seq_file *m, u8 *digest, u32 size)
 {
 	u32 i;
@@ -356,6 +436,28 @@ static const struct file_operations ima_ascii_measurements_ops = {
 	.release = ima_measurements_release,
 };
 
+static const struct seq_operations ima_ascii_measurements_staged_seqops = {
+	.start = ima_measurements_staged_start,
+	.next = ima_measurements_staged_next,
+	.stop = ima_measurements_stop,
+	.show = ima_ascii_measurements_show
+};
+
+static int ima_ascii_measurements_staged_open(struct inode *inode,
+					      struct file *file)
+{
+	return _ima_measurements_open(inode, file,
+				      &ima_ascii_measurements_staged_seqops);
+}
+
+static const struct file_operations ima_ascii_measurements_staged_ops = {
+	.open = ima_ascii_measurements_staged_open,
+	.read = seq_read,
+	.write = ima_measurements_staged_write,
+	.llseek = seq_lseek,
+	.release = ima_measurements_release,
+};
+
 static ssize_t ima_read_policy(char *path)
 {
 	void *data = NULL;
@@ -459,10 +561,21 @@ static const struct seq_operations ima_policy_seqops = {
 };
 #endif
 
-static int __init create_securityfs_measurement_lists(void)
+static int __init create_securityfs_measurement_lists(bool staging)
 {
+	const struct file_operations *ascii_ops = &ima_ascii_measurements_ops;
+	const struct file_operations *binary_ops = &ima_measurements_ops;
+	mode_t permissions = S_IRUSR | S_IRGRP;
+	const char *file_suffix = "";
 	int count = NR_BANKS(ima_tpm_chip);
 
+	if (staging) {
+		ascii_ops = &ima_ascii_measurements_staged_ops;
+		binary_ops = &ima_measurements_staged_ops;
+		file_suffix = "_staged";
+		permissions |= (S_IWUSR | S_IWGRP);
+	}
+
 	if (ima_sha1_idx >= NR_BANKS(ima_tpm_chip))
 		count++;
 
@@ -473,29 +586,32 @@ static int __init create_securityfs_measurement_lists(void)
 
 		if (algo == HASH_ALGO__LAST)
 			snprintf(file_name, sizeof(file_name),
-				 "ascii_runtime_measurements_tpm_alg_%x",
-				 ima_tpm_chip->allocated_banks[i].alg_id);
+				 "ascii_runtime_measurements_tpm_alg_%x%s",
+				 ima_tpm_chip->allocated_banks[i].alg_id,
+				 file_suffix);
 		else
 			snprintf(file_name, sizeof(file_name),
-				 "ascii_runtime_measurements_%s",
-				 hash_algo_name[algo]);
-		dentry = securityfs_create_file(file_name, S_IRUSR | S_IRGRP,
+				 "ascii_runtime_measurements_%s%s",
+				 hash_algo_name[algo], file_suffix);
+		dentry = securityfs_create_file(file_name, permissions,
 						ima_dir, (void *)(uintptr_t)i,
-						&ima_ascii_measurements_ops);
+						ascii_ops);
 		if (IS_ERR(dentry))
 			return PTR_ERR(dentry);
 
 		if (algo == HASH_ALGO__LAST)
 			snprintf(file_name, sizeof(file_name),
-				 "binary_runtime_measurements_tpm_alg_%x",
-				 ima_tpm_chip->allocated_banks[i].alg_id);
+				 "binary_runtime_measurements_tpm_alg_%x%s",
+				 ima_tpm_chip->allocated_banks[i].alg_id,
+				 file_suffix);
 		else
 			snprintf(file_name, sizeof(file_name),
-				 "binary_runtime_measurements_%s",
-				 hash_algo_name[algo]);
-		dentry = securityfs_create_file(file_name, S_IRUSR | S_IRGRP,
+				 "binary_runtime_measurements_%s%s",
+				 hash_algo_name[algo], file_suffix);
+
+		dentry = securityfs_create_file(file_name, permissions,
 						ima_dir, (void *)(uintptr_t)i,
-						&ima_measurements_ops);
+						binary_ops);
 		if (IS_ERR(dentry))
 			return PTR_ERR(dentry);
 	}
@@ -503,6 +619,23 @@ static int __init create_securityfs_measurement_lists(void)
 	return 0;
 }
 
+static int __init create_securityfs_staging_links(void)
+{
+	struct dentry *dentry;
+
+	dentry = securityfs_create_symlink("binary_runtime_measurements_staged",
+		ima_dir, "binary_runtime_measurements_sha1_staged", NULL);
+	if (IS_ERR(dentry))
+		return PTR_ERR(dentry);
+
+	dentry = securityfs_create_symlink("ascii_runtime_measurements_staged",
+		ima_dir, "ascii_runtime_measurements_sha1_staged", NULL);
+	if (IS_ERR(dentry))
+		return PTR_ERR(dentry);
+
+	return 0;
+}
+
 /*
  * ima_open_policy: sequentialize access to the policy file
  */
@@ -595,7 +728,13 @@ int __init ima_fs_init(void)
 		goto out;
 	}
 
-	ret = create_securityfs_measurement_lists();
+	ret = create_securityfs_measurement_lists(false);
+	if (ret == 0 && IS_ENABLED(CONFIG_IMA_STAGING)) {
+		ret = create_securityfs_measurement_lists(true);
+		if (ret == 0)
+			ret = create_securityfs_staging_links();
+	}
+
 	if (ret != 0)
 		goto out;
 
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index d7d0fb639d99..d5503dd5cc9b 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -42,8 +42,8 @@ void ima_measure_kexec_event(const char *event_name)
 	long len;
 	int n;
 
-	buf_size = ima_get_binary_runtime_size(BINARY);
-	len = atomic_long_read(&ima_num_entries[BINARY]);
+	buf_size = ima_get_binary_runtime_size(BINARY_FULL);
+	len = atomic_long_read(&ima_num_entries[BINARY_FULL]);
 
 	n = scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
 		      "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;"
@@ -106,13 +106,26 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
 
 	memset(&khdr, 0, sizeof(khdr));
 	khdr.version = 1;
-	/* This is an append-only list, no need to hold the RCU read lock */
-	list_for_each_entry_rcu(qe, &ima_measurements, later, true) {
+	/* It can race with ima_queue_stage() and ima_queue_delete_staged(). */
+	mutex_lock(&ima_extend_list_mutex);
+
+	list_for_each_entry_rcu(qe, &ima_measurements_staged, later,
+				lockdep_is_held(&ima_extend_list_mutex)) {
 		ret = ima_dump_measurement(&khdr, qe);
 		if (ret < 0)
 			break;
 	}
 
+	list_for_each_entry_rcu(qe, &ima_measurements, later,
+				lockdep_is_held(&ima_extend_list_mutex)) {
+		if (!ret)
+			ret = ima_dump_measurement(&khdr, qe);
+		if (ret < 0)
+			break;
+	}
+
+	mutex_unlock(&ima_extend_list_mutex);
+
 	/*
 	 * fill in reserved space with some buffer details
 	 * (eg. version, buffer size, number of measurements)
@@ -167,6 +180,7 @@ void ima_add_kexec_buffer(struct kimage *image)
 		extra_memory = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;
 
 	binary_runtime_size = ima_get_binary_runtime_size(BINARY) +
+			      ima_get_binary_runtime_size(BINARY_STAGED) +
 			      extra_memory;
 
 	if (binary_runtime_size >= ULONG_MAX - PAGE_SIZE)
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index b6d10dceb669..50519ed837d4 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -26,6 +26,7 @@
 static struct tpm_digest *digests;
 
 LIST_HEAD(ima_measurements);	/* list of all measurements */
+LIST_HEAD(ima_measurements_staged); /* list of staged measurements */
 #ifdef CONFIG_IMA_KEXEC
 static unsigned long binary_runtime_size[BINARY__LAST];
 #else
@@ -45,11 +46,11 @@ atomic_long_t ima_num_violations = ATOMIC_LONG_INIT(0);
 /* key: inode (before secure-hashing a file) */
 struct hlist_head __rcu *ima_htable;
 
-/* mutex protects atomicity of extending measurement list
+/* mutex protects atomicity of extending and staging measurement list
  * and extending the TPM PCR aggregate. Since tpm_extend can take
  * long (and the tpm driver uses a mutex), we can't use the spinlock.
  */
-static DEFINE_MUTEX(ima_extend_list_mutex);
+DEFINE_MUTEX(ima_extend_list_mutex);
 
 /*
  * Used internally by the kernel to suspend measurements.
@@ -174,12 +175,16 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
 				lockdep_is_held(&ima_extend_list_mutex));
 
 	atomic_long_inc(&ima_num_entries[BINARY]);
+	atomic_long_inc(&ima_num_entries[BINARY_FULL]);
+
 	if (update_htable) {
 		key = ima_hash_key(entry->digests[ima_hash_algo_idx].digest);
 		hlist_add_head_rcu(&qe->hnext, &htable[key]);
 	}
 
 	ima_update_binary_runtime_size(entry, BINARY);
+	ima_update_binary_runtime_size(entry, BINARY_FULL);
+
 	return 0;
 }
 
@@ -280,6 +285,94 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
 	return result;
 }
 
+int ima_queue_stage(void)
+{
+	int ret = 0;
+
+	mutex_lock(&ima_extend_list_mutex);
+	if (!list_empty(&ima_measurements_staged)) {
+		ret = -EEXIST;
+		goto out_unlock;
+	}
+
+	if (list_empty(&ima_measurements)) {
+		ret = -ENOENT;
+		goto out_unlock;
+	}
+
+	list_replace(&ima_measurements, &ima_measurements_staged);
+	INIT_LIST_HEAD(&ima_measurements);
+
+	atomic_long_set(&ima_num_entries[BINARY_STAGED],
+			atomic_long_read(&ima_num_entries[BINARY]));
+	atomic_long_set(&ima_num_entries[BINARY], 0);
+
+	if (IS_ENABLED(CONFIG_IMA_KEXEC)) {
+		binary_runtime_size[BINARY_STAGED] =
+					binary_runtime_size[BINARY];
+		binary_runtime_size[BINARY] = 0;
+	}
+out_unlock:
+	mutex_unlock(&ima_extend_list_mutex);
+	return ret;
+}
+
+static void ima_queue_delete(struct list_head *head);
+
+int ima_queue_staged_delete_all(void)
+{
+	LIST_HEAD(ima_measurements_trim);
+
+	mutex_lock(&ima_extend_list_mutex);
+	if (list_empty(&ima_measurements_staged)) {
+		mutex_unlock(&ima_extend_list_mutex);
+		return -ENOENT;
+	}
+
+	list_replace(&ima_measurements_staged, &ima_measurements_trim);
+	INIT_LIST_HEAD(&ima_measurements_staged);
+
+	atomic_long_set(&ima_num_entries[BINARY_STAGED], 0);
+
+	if (IS_ENABLED(CONFIG_IMA_KEXEC))
+		binary_runtime_size[BINARY_STAGED] = 0;
+
+	mutex_unlock(&ima_extend_list_mutex);
+
+	ima_queue_delete(&ima_measurements_trim);
+	return 0;
+}
+
+static void ima_queue_delete(struct list_head *head)
+{
+	struct ima_queue_entry *qe, *qe_tmp;
+	unsigned int i;
+
+	list_for_each_entry_safe(qe, qe_tmp, head, later) {
+		/*
+		 * Safe to free template_data here without synchronize_rcu()
+		 * because the only htable reader, ima_lookup_digest_entry(),
+		 * accesses only entry->digests, not template_data. If new
+		 * htable readers are added that access template_data, a
+		 * synchronize_rcu() is required here.
+		 */
+		for (i = 0; i < qe->entry->template_desc->num_fields; i++) {
+			kfree(qe->entry->template_data[i].data);
+			qe->entry->template_data[i].data = NULL;
+			qe->entry->template_data[i].len = 0;
+		}
+
+		list_del(&qe->later);
+
+		/* No leak if condition is false, referenced by ima_htable. */
+		if (IS_ENABLED(CONFIG_IMA_DISABLE_HTABLE)) {
+			kfree(qe->entry->digests);
+			kfree(qe->entry);
+			kfree(qe);
+		}
+	}
+}
+
 int ima_restore_measurement_entry(struct ima_template_entry *entry)
 {
 	int result = 0;
-- 
2.43.0

[PATCH v4 10/13] ima: Add support for flushing the hash table when staging measurements

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Introduce the new kernel option ima_flush_htable to decide whether or not
the digests of staged measurement entries are flushed from the hash table,
when they are deleted.

When the option is enabled, replace the old hash table with a new one,
by calling ima_alloc_replace_htable(), and completely delete the
measurements entries.

Note: This code derives from the Alt-IMA Huawei project, whose license is
      GPL-2.0 OR MIT.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 .../admin-guide/kernel-parameters.txt         |  4 +++
 security/integrity/ima/ima.h                  |  1 +
 security/integrity/ima/ima_queue.c            | 36 ++++++++++++++++---
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 89670c5e7c8e..a651a3864dcf 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2345,6 +2345,10 @@ Kernel parameters
 			Use the canonical format for the binary runtime
 			measurements, instead of host native format.
 
+	ima_flush_htable  [IMA]
+			Flush the IMA hash table when deleting all the
+			staged measurement entries.
+
 	ima_hash=	[IMA]
 			Format: { md5 | sha1 | rmd160 | sha256 | sha384
 				   | sha512 | ... }
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 65db152a0a24..699b735dec7d 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -340,6 +340,7 @@ extern atomic_long_t ima_num_entries[BINARY__LAST];
 extern atomic_long_t ima_num_violations;
 extern struct hlist_head __rcu *ima_htable;
 extern struct mutex ima_extend_list_mutex;
+extern bool ima_flush_htable;
 
 static inline unsigned int ima_hash_key(u8 *digest)
 {
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 50519ed837d4..f5c18acfbc43 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -22,6 +22,20 @@
 
 #define AUDIT_CAUSE_LEN_MAX 32
 
+bool ima_flush_htable;
+
+static int __init ima_flush_htable_setup(char *str)
+{
+	if (IS_ENABLED(CONFIG_IMA_DISABLE_HTABLE)) {
+		pr_warn("Hash table not enabled, ignoring request to flush\n");
+		return 1;
+	}
+
+	ima_flush_htable = true;
+	return 1;
+}
+__setup("ima_flush_htable", ima_flush_htable_setup);
+
 /* pre-allocated array of tpm_digest structures to extend a PCR */
 static struct tpm_digest *digests;
 
@@ -317,10 +331,11 @@ int ima_queue_stage(void)
 	return ret;
 }
 
-static void ima_queue_delete(struct list_head *head);
+static void ima_queue_delete(struct list_head *head, bool flush_htable);
 
 int ima_queue_staged_delete_all(void)
 {
+	struct hlist_head *old_queue = NULL;
 	LIST_HEAD(ima_measurements_trim);
 
 	mutex_lock(&ima_extend_list_mutex);
@@ -337,13 +352,26 @@ int ima_queue_staged_delete_all(void)
 	if (IS_ENABLED(CONFIG_IMA_KEXEC))
 		binary_runtime_size[BINARY_STAGED] = 0;
 
+	if (ima_flush_htable) {
+		old_queue = ima_alloc_replace_htable();
+		if (IS_ERR(old_queue)) {
+			mutex_unlock(&ima_extend_list_mutex);
+			return PTR_ERR(old_queue);
+		}
+	}
+
 	mutex_unlock(&ima_extend_list_mutex);
 
-	ima_queue_delete(&ima_measurements_trim);
+	if (ima_flush_htable) {
+		synchronize_rcu();
+		kfree(old_queue);
+	}
+
+	ima_queue_delete(&ima_measurements_trim, ima_flush_htable);
 	return 0;
 }
 
-static void ima_queue_delete(struct list_head *head)
+static void ima_queue_delete(struct list_head *head, bool flush_htable)
 {
 	struct ima_queue_entry *qe, *qe_tmp;
 	unsigned int i;
@@ -365,7 +393,7 @@ static void ima_queue_delete(struct list_head *head)
 		list_del(&qe->later);
 
 		/* No leak if condition is false, referenced by ima_htable. */
-		if (IS_ENABLED(CONFIG_IMA_DISABLE_HTABLE)) {
+		if (IS_ENABLED(CONFIG_IMA_DISABLE_HTABLE) || flush_htable) {
 			kfree(qe->entry->digests);
 			kfree(qe->entry);
 			kfree(qe);
-- 
2.43.0

[PATCH v4 11/13] ima: Support staging and deleting N measurements entries

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Add support for sending a value N between 1 and ULONG_MAX to the staging
interface. This value represents the number of measurements that should be
deleted from the current measurements list.

This staging method allows the remote attestation agents to easily separate
the measurements that were verified (staged and deleted) from those that
weren't due to the race between taking a TPM quote and reading the
measurements list.

In order to minimize the locking time of ima_extend_list_mutex, deleting
N entries is realized by staging the entire current measurements list
(with the lock), by determining the N-th staged entry (without the lock),
and by splicing the entries in excess back to the current measurements list
(with the lock). Finally, the N entries are deleted (without the lock).

Flushing the hash table is not supported for N entries, since it would
require removing the N entries one by one from the hash table under the
ima_extend_list_mutex lock, which would increase the locking time.

The ima_extend_list_mutex lock is necessary in ima_dump_measurement_list()
because ima_queue_staged_delete_partial() uses __list_cut_position() to
modify ima_measurements_staged, for which no RCU-safe variant exists. For
the staging with prompt flavor alone, list_replace_rcu() could have been
used instead, but since both flavors share the same kexec serialization
path, the mutex is required regardless.

Link: https://github.com/linux-integrity/linux/issues/1
Suggested-by: Steven Chen <chenste@linux.microsoft.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/Kconfig     |  3 ++
 security/integrity/ima/ima.h       |  1 +
 security/integrity/ima/ima_fs.c    | 22 +++++++++-
 security/integrity/ima/ima_queue.c | 70 ++++++++++++++++++++++++++++++
 4 files changed, 95 insertions(+), 1 deletion(-)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index e714726f3384..6ddb4e77bff5 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -341,6 +341,9 @@ config IMA_STAGING
 	  It allows user space to stage the measurements list for deletion and
 	  to delete the staged measurements after confirmation.
 
+	  Or, alternatively, it allows user space to specify N measurements
+	  entries to be deleted.
+
 	  On kexec, staging is reverted and staged measurements are prepended
 	  to the current measurements list when measurements are copied to the
 	  secondary kernel.
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 699b735dec7d..de0693fce53c 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -319,6 +319,7 @@ struct ima_template_desc *lookup_template_desc(const char *name);
 bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
 int ima_queue_stage(void);
 int ima_queue_staged_delete_all(void);
+int ima_queue_staged_delete_partial(unsigned long req_value);
 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);
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 39d9128e9f22..eb3f343c1138 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -28,6 +28,7 @@
  * Requests:
  * 'A\n': stage the entire measurements list
  * 'D\n': delete all staged measurements
+ * '[1, ULONG_MAX]\n' delete N measurements entries
  */
 #define STAGED_REQ_LENGTH 21
 
@@ -319,6 +320,7 @@ static ssize_t ima_measurements_staged_write(struct file *file,
 					     size_t datalen, loff_t *ppos)
 {
 	char req[STAGED_REQ_LENGTH];
+	unsigned long req_value;
 	int ret;
 
 	if (*ppos > 0 || datalen < 2 || datalen > STAGED_REQ_LENGTH)
@@ -346,7 +348,25 @@ static ssize_t ima_measurements_staged_write(struct file *file,
 		ret = ima_queue_staged_delete_all();
 		break;
 	default:
-		ret = -EINVAL;
+		if (ima_flush_htable) {
+			pr_debug("Deleting staged N measurements not supported when flushing the hash table is requested\n");
+			return -EINVAL;
+		}
+
+		ret = kstrtoul(req, 10, &req_value);
+		if (ret < 0)
+			return ret;
+
+		if (req_value == 0) {
+			pr_debug("Must delete at least one entry\n");
+			return -EINVAL;
+		}
+
+		ret = ima_queue_stage();
+		if (ret < 0)
+			return ret;
+
+		ret = ima_queue_staged_delete_partial(req_value);
 	}
 
 	if (ret < 0)
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index f5c18acfbc43..4fb557d61a88 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -371,6 +371,76 @@ int ima_queue_staged_delete_all(void)
 	return 0;
 }
 
+int ima_queue_staged_delete_partial(unsigned long req_value)
+{
+	unsigned long req_value_copy = req_value;
+	unsigned long size_to_remove = 0, num_to_remove = 0;
+	struct list_head *cut_pos = NULL;
+	LIST_HEAD(ima_measurements_trim);
+	struct ima_queue_entry *qe;
+	int ret = 0;
+
+	/*
+	 * Safe walk (no concurrent write), not under ima_extend_list_mutex
+	 * for performance reasons.
+	 */
+	list_for_each_entry(qe, &ima_measurements_staged, later) {
+		size_to_remove += get_binary_runtime_size(qe->entry);
+		num_to_remove++;
+
+		if (--req_value_copy == 0) {
+			/* qe->later always points to a valid list entry. */
+			cut_pos = &qe->later;
+			break;
+		}
+	}
+
+	/* Nothing to remove, undoing staging. */
+	if (req_value_copy > 0) {
+		size_to_remove = 0;
+		num_to_remove = 0;
+		ret = -ENOENT;
+	}
+
+	mutex_lock(&ima_extend_list_mutex);
+	if (list_empty(&ima_measurements_staged)) {
+		mutex_unlock(&ima_extend_list_mutex);
+		return -ENOENT;
+	}
+
+	if (cut_pos != NULL)
+		/*
+		 * ima_dump_measurement_list() does not modify the list,
+		 * cut_pos remains the same even if it was computed before
+		 * the lock.
+		 */
+		__list_cut_position(&ima_measurements_trim,
+				    &ima_measurements_staged, cut_pos);
+
+	atomic_long_sub(num_to_remove, &ima_num_entries[BINARY_STAGED]);
+	atomic_long_add(atomic_long_read(&ima_num_entries[BINARY_STAGED]),
+			&ima_num_entries[BINARY]);
+	atomic_long_set(&ima_num_entries[BINARY_STAGED], 0);
+
+	if (IS_ENABLED(CONFIG_IMA_KEXEC)) {
+		binary_runtime_size[BINARY_STAGED] -= size_to_remove;
+		binary_runtime_size[BINARY] +=
+					binary_runtime_size[BINARY_STAGED];
+		binary_runtime_size[BINARY_STAGED] = 0;
+	}
+
+	/*
+	 * Splice (prepend) any remaining non-deleted staged entries to the
+	 * active list (RCU not needed, there cannot be concurrent readers).
+	 */
+	list_splice(&ima_measurements_staged, &ima_measurements);
+	INIT_LIST_HEAD(&ima_measurements_staged);
+	mutex_unlock(&ima_extend_list_mutex);
+
+	ima_queue_delete(&ima_measurements_trim, false);
+	return ret;
+}
+
 static void ima_queue_delete(struct list_head *head, bool flush_htable)
 {
 	struct ima_queue_entry *qe, *qe_tmp;
-- 
2.43.0

[PATCH v4 12/13] ima: Return error on deleting staged measurements after kexec

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Refuse to delete staged measurements (both with prompt and without) if
a kexec racing with the deletion already prepended staged measurements in
the kexec buffer. In this way, user space becomes aware that staged
measurements are going to appear in the secondary kernel, and thus they
don't have to be saved twice.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/ima/ima.h       |  1 +
 security/integrity/ima/ima_kexec.c |  3 +++
 security/integrity/ima/ima_queue.c | 17 +++++++++++++++++
 3 files changed, 21 insertions(+)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index de0693fce53c..0816b69f7c39 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -342,6 +342,7 @@ extern atomic_long_t ima_num_violations;
 extern struct hlist_head __rcu *ima_htable;
 extern struct mutex ima_extend_list_mutex;
 extern bool ima_flush_htable;
+extern bool ima_staged_measurements_prepended;
 
 static inline unsigned int ima_hash_key(u8 *digest)
 {
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index d5503dd5cc9b..25c8356be22a 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -116,6 +116,9 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
 			break;
 	}
 
+	if (!list_empty(&ima_measurements_staged))
+		ima_staged_measurements_prepended = true;
+
 	list_for_each_entry_rcu(qe, &ima_measurements, later,
 				lockdep_is_held(&ima_extend_list_mutex)) {
 		if (!ret)
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 4fb557d61a88..1918c8ea9abb 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -72,6 +72,13 @@ DEFINE_MUTEX(ima_extend_list_mutex);
  */
 static bool ima_measurements_suspended;
 
+/*
+ * Used to determine if staged measurements were prepended during kexec,
+ * so that an error can be sent to user space during deletion, and they don't
+ * store staged measurements twice.
+ */
+bool ima_staged_measurements_prepended;
+
 /* Callers must call synchronize_rcu() and free the hash table. */
 static struct hlist_head *ima_alloc_replace_htable(void)
 {
@@ -344,6 +351,11 @@ int ima_queue_staged_delete_all(void)
 		return -ENOENT;
 	}
 
+	if (ima_staged_measurements_prepended) {
+		mutex_unlock(&ima_extend_list_mutex);
+		return -ESTALE;
+	}
+
 	list_replace(&ima_measurements_staged, &ima_measurements_trim);
 	INIT_LIST_HEAD(&ima_measurements_staged);
 
@@ -408,6 +420,11 @@ int ima_queue_staged_delete_partial(unsigned long req_value)
 		return -ENOENT;
 	}
 
+	if (ima_staged_measurements_prepended) {
+		mutex_unlock(&ima_extend_list_mutex);
+		return -ESTALE;
+	}
+
 	if (cut_pos != NULL)
 		/*
 		 * ima_dump_measurement_list() does not modify the list,
-- 
2.43.0

[PATCH v4 13/13] doc: security: Add documentation of the IMA staging mechanism

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Add the documentation of the IMA staging mechanism in
Documentation/security/IMA-staging.rst.

Also add the missing Documentation/security/IMA-templates.rst file in
MAINTAINERS.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 Documentation/security/IMA-staging.rst | 159 +++++++++++++++++++++++++
 Documentation/security/index.rst       |   1 +
 MAINTAINERS                            |   2 +
 3 files changed, 162 insertions(+)
 create mode 100644 Documentation/security/IMA-staging.rst

diff --git a/Documentation/security/IMA-staging.rst b/Documentation/security/IMA-staging.rst
new file mode 100644
index 000000000000..d0c27c0435c0
--- /dev/null
+++ b/Documentation/security/IMA-staging.rst
@@ -0,0 +1,159 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==================================
+IMA Measurements Staging Mechanism
+==================================
+
+
+Introduction
+============
+
+The IMA measurements list is currently stored in the kernel memory. Memory
+occupation grows linearly with the number of entries, and can become a
+problem especially in environments with reduced resources.
+
+While there is an advantage in keeping the IMA measurements list in kernel
+memory, so that it is always available for reading from the securityfs
+interfaces, storing it elsewhere would make it possible to free precious
+memory for other kernel components.
+
+Storing the IMA measurements list outside the kernel does not introduce
+security issues, since its integrity is anyway protected by the TPM.
+
+Hence, the new IMA staging mechanism is introduced to allow user space
+to remove the desired portion of the measurements list from the kernel.
+
+
+Usage
+=====
+
+The IMA staging mechanism can be enabled from the kernel configuration with
+the CONFIG_IMA_STAGING option.
+
+If it is enabled, IMA duplicates the current measurements interfaces (both
+binary and ASCII), by adding the ``_staged`` file suffix. Unlike the
+existing counterparts, the ``_staged`` interfaces have write permission for
+the root user and group, and require the process to have CAP_SYS_ADMIN set.
+
+The staging mechanism supports two flavors.
+
+
+Staging with prompt
+~~~~~~~~~~~~~~~~~~~
+
+This staging process is achieved with the following steps.
+
+ 1. ``echo A > <_staged interface>``: the user requests IMA to stage the
+    entire measurements list;
+ 2. ``cat <_staged interface>``: the user reads the staged measurements;
+ 3. ``echo D > <_staged interface>`` : the user request IMA to delete
+    staged measurements.
+
+
+Staging and deleting
+~~~~~~~~~~~~~~~~~~~~
+
+This staging process is achieved with the following steps.
+
+ 1. ``cat <_non_staged interface>``: the user reads the current
+    measurements list and determines what the value N for staging should
+    be;
+ 2. ``echo N > <_staged interface>``: the user requests IMA to delete N
+    measurements from the current measurements list.
+
+
+Interface Access
+================
+
+In order to avoid the IMA measurements list be suddenly truncated by the
+staging mechanism during a read, or having multiple concurrent staging, a
+semaphore-like locking scheme has been implemented on all the measurements
+list interfaces.
+
+Multiple readers can access concurrently the non-staged interfaces, and
+they can be in mutual exclusion with one writer accessing the staged
+interfaces.
+
+If an illegal access occurs, the open to the measurements list interface is
+denied.
+
+
+Management of Staged Measurements
+=================================
+
+Since with the staging mechanism measurements entries are removed from the
+kernel, the user needs to save the staged ones in a storage and concatenate
+them together, so that it can present them to remote attestation agents as
+if staging was never done.
+
+Coordination is necessary in the case where there are multiple actors
+requesting measurements to be staged.
+
+In the staging with prompt case, the staging interface can be accessed only
+by one actor at time, so the others will get an error until the former
+closes it. Since the actors don't care about N, when they gain access to
+the interface, they will get all the staged measurements at the time of
+their request.
+
+In the case of staging and deleting, coordination is more important, since
+there is the risk that two actors unaware of each other compute the value N
+on the current measurements list and request IMA to stage N twice.
+
+
+Remote Attestation Agent Workflow
+=================================
+
+Users can choose the staging method they find more appropriate for their
+workflow.
+
+If, as an example, a remote attestation agent would like to present to the
+remote attestation server only the measurements that are required to
+verify the TPM quote, its workflow would be the following.
+
+With staging with prompt, the agent stages the current measurements list,
+reads and stores the measurements in a storage and immediately requests
+IMA to delete the staged measurements from kernel memory. Afterwards, it
+calculates N by replaying the PCR extend on the stored measurements until
+the calculated PCRs match the quoted PCRs. It then keeps the measurements
+in excess for the next attestation request.
+
+At the next attestation request, the agent performs the same steps above,
+and concatenates the new measurements to the ones in excess from the
+previous request. Also in this case, the agent replays the PCR extend until
+it matches the currently quoted PCRs, keeps the measurements in excess and
+presents the new N measurements entries to the remote attestation server.
+
+With the staging with deleting method, the agents reads the current
+measurements list, calculates N and requests IMA to delete only those. The
+measurements in excess are kept in the IMA measurements list and can be
+retrieved at the next remote attestation request.
+
+Kexec
+=====
+
+In the event a kexec() system call occurs between staging and deleting, the
+staged measurements entries are prepended to the current measurements lists,
+so that they are both available when the secondary kernel starts. In that
+case, IMA returns an error to the user when attempting to delete staged
+measurements to notify about their copy to the kexec buffer, so that the
+user does not store them twice.
+
+
+Hash table
+==========
+
+By default, the template digest of staged measurement entries are kept in
+kernel memory (only template data are freed), to be able to detect
+duplicate entries independently of staging.
+
+The new kernel option ``ima_flush_htable`` has been introduced to
+explicitly request a complete deletion of the staged measurements, for
+maximum kernel memory saving. If the option has been specified, duplicate
+entries are still avoided on entries of the current measurements list,
+but there can be duplicates between different groups of staged
+measurements.
+
+Flushing the hash table is supported only for the staging with prompt
+flavor. For the staging and deleting flavor, it would have been necessary
+to lock the hot path adding new measurements for the time needed to remove
+each staged measurement individually.
diff --git a/Documentation/security/index.rst b/Documentation/security/index.rst
index 3e0a7114a862..cec064dc1c83 100644
--- a/Documentation/security/index.rst
+++ b/Documentation/security/index.rst
@@ -8,6 +8,7 @@ Security Documentation
    credentials
    snp-tdx-threat-model
    IMA-templates
+   IMA-staging
    keys/index
    lsm
    lsm-development
diff --git a/MAINTAINERS b/MAINTAINERS
index 04823afa8b74..e78dfb4f4482 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12668,6 +12668,8 @@ R:	Eric Snowberg <eric.snowberg@oracle.com>
 L:	linux-integrity@vger.kernel.org
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git
+F:	Documentation/security/IMA-staging.rst
+F:	Documentation/security/IMA-templates.rst
 F:	include/linux/secure_boot.h
 F:	security/integrity/
 F:	security/integrity/ima/
-- 
2.43.0

Re: [PATCH v4 09/13] ima: Add support for staging measurements with prompt

[steven chen]

On 3/26/2026 10:30 AM, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.com>
>
> Introduce the ability of staging the IMA measurement list and deleting them
> with a prompt.
>
> Staging means moving the current content of the measurement list to a
> separate location, and allowing users to read and delete it. This causes
> the measurement list to be atomically truncated before new measurements can
> be added. Staging can be done only once at a time. In the event of kexec(),
> staging is reverted and staged entries will be carried over to the new
> kernel.
>
> Introduce ascii_runtime_measurements_<algo>_staged and
> binary_runtime_measurements_<algo>_staged interfaces to stage and delete
> the measurements. Use 'echo A > <IMA interface>' and
> 'echo D > <IMA interface>' to respectively stage and delete the entire
> measurements list. Locking of these interfaces is also mediated with a call
> to _ima_measurements_open() and with ima_measurements_release().
>
> Implement the staging functionality by introducing the new global
> measurements list ima_measurements_staged, and ima_queue_stage() and
> ima_queue_delete_staged_all() to respectively move measurements from the
> current measurements list to the staged one, and to move staged
> measurements to the ima_measurements_trim list for deletion. Introduce
> ima_queue_delete() to delete the measurements.
>
> Finally, introduce the BINARY_STAGED AND BINARY_FULL binary measurements
> list types, to maintain the counters and the binary size of staged
> measurements and the full measurements list (including entries that were
> staged). BINARY still represents the current binary measurements list.
>
> Use the binary size for the BINARY + BINARY_STAGED types in
> ima_add_kexec_buffer(), since both measurements list types are copied to
> the secondary kernel during kexec. Use BINARY_FULL in
> ima_measure_kexec_event(), to generate a critical data record.
>
> It should be noted that the BINARY_FULL counter is not passed through
> kexec. Thus, the number of entries included in the kexec critical data
> records refers to the entries since the previous kexec records.
>
> Note: This code derives from the Alt-IMA Huawei project, whose license is
>        GPL-2.0 OR MIT.
>
> Link: https://github.com/linux-integrity/linux/issues/1
> Suggested-by: Gregory Lumen <gregorylumen@linux.microsoft.com> (staging revert)
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
>   security/integrity/ima/Kconfig     |  13 +++
>   security/integrity/ima/ima.h       |   8 +-
>   security/integrity/ima/ima_fs.c    | 167 ++++++++++++++++++++++++++---
>   security/integrity/ima/ima_kexec.c |  22 +++-
>   security/integrity/ima/ima_queue.c |  97 ++++++++++++++++-
>   5 files changed, 286 insertions(+), 21 deletions(-)
>
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index 976e75f9b9ba..e714726f3384 100644
> --- a/security/integrity/ima/Kconfig
> +++ b/security/integrity/ima/Kconfig
> @@ -332,4 +332,17 @@ config IMA_KEXEC_EXTRA_MEMORY_KB
>   	  If set to the default value of 0, an extra half page of memory for those
>   	  additional measurements will be allocated.
>   
> +config IMA_STAGING
> +	bool "Support for staging the measurements list"
> +	default y
> +	help
> +	  Add support for staging the measurements list.
> +
> +	  It allows user space to stage the measurements list for deletion and
> +	  to delete the staged measurements after confirmation.
> +
> +	  On kexec, staging is reverted and staged measurements are prepended
> +	  to the current measurements list when measurements are copied to the
> +	  secondary kernel.
> +
>   endif
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 97b7d6024b5d..65db152a0a24 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -30,9 +30,11 @@ enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8, TPM_PCR10 = 10 };
>   
>   /*
>    * BINARY: current binary measurements list
> + * BINARY_STAGED: staged binary measurements list
> + * BINARY_FULL: binary measurements list since IMA init (lost after kexec)
>    */
>   enum binary_lists {
> -	BINARY, BINARY__LAST
> +	BINARY, BINARY_STAGED, BINARY_FULL, BINARY__LAST
>   };
>   
>   /* digest size for IMA, fits SHA1 or MD5 */
> @@ -125,6 +127,7 @@ struct ima_queue_entry {
>   	struct ima_template_entry *entry;
>   };
>   extern struct list_head ima_measurements;	/* list of all measurements */
> +extern struct list_head ima_measurements_staged; /* list of staged meas. */
>   
>   /* Some details preceding the binary serialized measurement list */
>   struct ima_kexec_hdr {
> @@ -314,6 +317,8 @@ struct ima_template_desc *ima_template_desc_current(void);
>   struct ima_template_desc *ima_template_desc_buf(void);
>   struct ima_template_desc *lookup_template_desc(const char *name);
>   bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
> +int ima_queue_stage(void);
> +int ima_queue_staged_delete_all(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);
> @@ -334,6 +339,7 @@ extern spinlock_t ima_queue_lock;
>   extern atomic_long_t ima_num_entries[BINARY__LAST];
>   extern atomic_long_t ima_num_violations;
>   extern struct hlist_head __rcu *ima_htable;
> +extern struct mutex ima_extend_list_mutex;
>   
>   static inline unsigned int ima_hash_key(u8 *digest)
>   {
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index 7709a4576322..39d9128e9f22 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -24,6 +24,13 @@
>   
>   #include "ima.h"
>   
> +/*
> + * Requests:
> + * 'A\n': stage the entire measurements list
> + * 'D\n': delete all staged measurements
> + */
> +#define STAGED_REQ_LENGTH 21
> +
>   static DEFINE_MUTEX(ima_write_mutex);
>   static DEFINE_MUTEX(ima_measure_mutex);
>   static long ima_measure_users;
> @@ -97,6 +104,11 @@ static void *ima_measurements_start(struct seq_file *m, loff_t *pos)
>   	return _ima_measurements_start(m, pos, &ima_measurements);
>   }
>   
> +static void *ima_measurements_staged_start(struct seq_file *m, loff_t *pos)
> +{
> +	return _ima_measurements_start(m, pos, &ima_measurements_staged);
> +}
> +
>   static void *_ima_measurements_next(struct seq_file *m, void *v, loff_t *pos,
>   				    struct list_head *head)
>   {
> @@ -118,6 +130,12 @@ static void *ima_measurements_next(struct seq_file *m, void *v, loff_t *pos)
>   	return _ima_measurements_next(m, v, pos, &ima_measurements);
>   }
>   
> +static void *ima_measurements_staged_next(struct seq_file *m, void *v,
> +					  loff_t *pos)
> +{
> +	return _ima_measurements_next(m, v, pos, &ima_measurements_staged);
> +}
> +
>   static void ima_measurements_stop(struct seq_file *m, void *v)
>   {
>   }
> @@ -283,6 +301,68 @@ static const struct file_operations ima_measurements_ops = {
>   	.release = ima_measurements_release,
>   };
>   
> +static const struct seq_operations ima_measurments_staged_seqops = {
> +	.start = ima_measurements_staged_start,
> +	.next = ima_measurements_staged_next,
> +	.stop = ima_measurements_stop,
> +	.show = ima_measurements_show
> +};
> +
> +static int ima_measurements_staged_open(struct inode *inode, struct file *file)
> +{
> +	return _ima_measurements_open(inode, file,
> +				      &ima_measurments_staged_seqops);
> +}
> +
> +static ssize_t ima_measurements_staged_write(struct file *file,
> +					     const char __user *buf,
> +					     size_t datalen, loff_t *ppos)
> +{
> +	char req[STAGED_REQ_LENGTH];
> +	int ret;
> +
> +	if (*ppos > 0 || datalen < 2 || datalen > STAGED_REQ_LENGTH)
> +		return -EINVAL;
> +
> +	if (copy_from_user(req, buf, datalen) != 0)
> +		return -EFAULT;
> +
> +	if (req[datalen - 1] != '\n')
> +		return -EINVAL;
> +
> +	req[datalen - 1] = '\0';
> +
> +	switch (req[0]) {
> +	case 'A':
> +		if (datalen != 2)
> +			return -EINVAL;
> +
> +		ret = ima_queue_stage();
> +		break;
> +	case 'D':
> +		if (datalen != 2)
> +			return -EINVAL;
> +
> +		ret = ima_queue_staged_delete_all();
> +		break;

I think the following two steps may not work because of race condition:

step1: ret = ima_queue_stage(); //this will put all logs in active list into staged list;
step2: ret = ima_queue_staged_delete_all(); //this will delete all logs in staged list;

The following is the step of race condition:
     1. current active log list LA1;
     2. user agent read the TPM quote QA1 match list LA1;
     3. new event NewLog is added into active log list LA1+NewLog
     4. user agent call ima_queue_stage() and generated staged list
        including LA1+NewLog.
     5. user agent call ima_queue_staged_delete_all();
        The new log NewLog in step 3 is also deleted

Next time the attestation will fail if using the active log list in the 
kernel.

Thanks,

Steven

> +	default:
> +		ret = -EINVAL;
> +	}
> +
> +	if (ret < 0)
> +		return ret;
> +
> +	return datalen;
> +}
> +
> +static const struct file_operations ima_measurements_staged_ops = {
> +	.open = ima_measurements_staged_open,
> +	.read = seq_read,
> +	.write = ima_measurements_staged_write,
> +	.llseek = seq_lseek,
> +	.release = ima_measurements_release,
> +};
> +
>   void ima_print_digest(struct seq_file *m, u8 *digest, u32 size)
>   {
>   	u32 i;
> @@ -356,6 +436,28 @@ static const struct file_operations ima_ascii_measurements_ops = {
>   	.release = ima_measurements_release,
>   };
>   
> +static const struct seq_operations ima_ascii_measurements_staged_seqops = {
> +	.start = ima_measurements_staged_start,
> +	.next = ima_measurements_staged_next,
> +	.stop = ima_measurements_stop,
> +	.show = ima_ascii_measurements_show
> +};
> +
> +static int ima_ascii_measurements_staged_open(struct inode *inode,
> +					      struct file *file)
> +{
> +	return _ima_measurements_open(inode, file,
> +				      &ima_ascii_measurements_staged_seqops);
> +}
> +
> +static const struct file_operations ima_ascii_measurements_staged_ops = {
> +	.open = ima_ascii_measurements_staged_open,
> +	.read = seq_read,
> +	.write = ima_measurements_staged_write,
> +	.llseek = seq_lseek,
> +	.release = ima_measurements_release,
> +};
> +
>   static ssize_t ima_read_policy(char *path)
>   {
>   	void *data = NULL;
> @@ -459,10 +561,21 @@ static const struct seq_operations ima_policy_seqops = {
>   };
>   #endif
>   
> -static int __init create_securityfs_measurement_lists(void)
> +static int __init create_securityfs_measurement_lists(bool staging)
>   {
> +	const struct file_operations *ascii_ops = &ima_ascii_measurements_ops;
> +	const struct file_operations *binary_ops = &ima_measurements_ops;
> +	mode_t permissions = S_IRUSR | S_IRGRP;
> +	const char *file_suffix = "";
>   	int count = NR_BANKS(ima_tpm_chip);
>   
> +	if (staging) {
> +		ascii_ops = &ima_ascii_measurements_staged_ops;
> +		binary_ops = &ima_measurements_staged_ops;
> +		file_suffix = "_staged";
> +		permissions |= (S_IWUSR | S_IWGRP);
> +	}
> +
>   	if (ima_sha1_idx >= NR_BANKS(ima_tpm_chip))
>   		count++;
>   
> @@ -473,29 +586,32 @@ static int __init create_securityfs_measurement_lists(void)
>   
>   		if (algo == HASH_ALGO__LAST)
>   			snprintf(file_name, sizeof(file_name),
> -				 "ascii_runtime_measurements_tpm_alg_%x",
> -				 ima_tpm_chip->allocated_banks[i].alg_id);
> +				 "ascii_runtime_measurements_tpm_alg_%x%s",
> +				 ima_tpm_chip->allocated_banks[i].alg_id,
> +				 file_suffix);
>   		else
>   			snprintf(file_name, sizeof(file_name),
> -				 "ascii_runtime_measurements_%s",
> -				 hash_algo_name[algo]);
> -		dentry = securityfs_create_file(file_name, S_IRUSR | S_IRGRP,
> +				 "ascii_runtime_measurements_%s%s",
> +				 hash_algo_name[algo], file_suffix);
> +		dentry = securityfs_create_file(file_name, permissions,
>   						ima_dir, (void *)(uintptr_t)i,
> -						&ima_ascii_measurements_ops);
> +						ascii_ops);
>   		if (IS_ERR(dentry))
>   			return PTR_ERR(dentry);
>   
>   		if (algo == HASH_ALGO__LAST)
>   			snprintf(file_name, sizeof(file_name),
> -				 "binary_runtime_measurements_tpm_alg_%x",
> -				 ima_tpm_chip->allocated_banks[i].alg_id);
> +				 "binary_runtime_measurements_tpm_alg_%x%s",
> +				 ima_tpm_chip->allocated_banks[i].alg_id,
> +				 file_suffix);
>   		else
>   			snprintf(file_name, sizeof(file_name),
> -				 "binary_runtime_measurements_%s",
> -				 hash_algo_name[algo]);
> -		dentry = securityfs_create_file(file_name, S_IRUSR | S_IRGRP,
> +				 "binary_runtime_measurements_%s%s",
> +				 hash_algo_name[algo], file_suffix);
> +
> +		dentry = securityfs_create_file(file_name, permissions,
>   						ima_dir, (void *)(uintptr_t)i,
> -						&ima_measurements_ops);
> +						binary_ops);
>   		if (IS_ERR(dentry))
>   			return PTR_ERR(dentry);
>   	}
> @@ -503,6 +619,23 @@ static int __init create_securityfs_measurement_lists(void)
>   	return 0;
>   }
>   
> +static int __init create_securityfs_staging_links(void)
> +{
> +	struct dentry *dentry;
> +
> +	dentry = securityfs_create_symlink("binary_runtime_measurements_staged",
> +		ima_dir, "binary_runtime_measurements_sha1_staged", NULL);
> +	if (IS_ERR(dentry))
> +		return PTR_ERR(dentry);
> +
> +	dentry = securityfs_create_symlink("ascii_runtime_measurements_staged",
> +		ima_dir, "ascii_runtime_measurements_sha1_staged", NULL);
> +	if (IS_ERR(dentry))
> +		return PTR_ERR(dentry);
> +
> +	return 0;
> +}
> +
>   /*
>    * ima_open_policy: sequentialize access to the policy file
>    */
> @@ -595,7 +728,13 @@ int __init ima_fs_init(void)
>   		goto out;
>   	}
>   
> -	ret = create_securityfs_measurement_lists();
> +	ret = create_securityfs_measurement_lists(false);
> +	if (ret == 0 && IS_ENABLED(CONFIG_IMA_STAGING)) {
> +		ret = create_securityfs_measurement_lists(true);
> +		if (ret == 0)
> +			ret = create_securityfs_staging_links();
> +	}
> +
>   	if (ret != 0)
>   		goto out;
>   
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index d7d0fb639d99..d5503dd5cc9b 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -42,8 +42,8 @@ void ima_measure_kexec_event(const char *event_name)
>   	long len;
>   	int n;
>   
> -	buf_size = ima_get_binary_runtime_size(BINARY);
> -	len = atomic_long_read(&ima_num_entries[BINARY]);
> +	buf_size = ima_get_binary_runtime_size(BINARY_FULL);
> +	len = atomic_long_read(&ima_num_entries[BINARY_FULL]);
>   
>   	n = scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
>   		      "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;"
> @@ -106,13 +106,26 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>   
>   	memset(&khdr, 0, sizeof(khdr));
>   	khdr.version = 1;
> -	/* This is an append-only list, no need to hold the RCU read lock */
> -	list_for_each_entry_rcu(qe, &ima_measurements, later, true) {
> +	/* It can race with ima_queue_stage() and ima_queue_delete_staged(). */
> +	mutex_lock(&ima_extend_list_mutex);
> +
> +	list_for_each_entry_rcu(qe, &ima_measurements_staged, later,
> +				lockdep_is_held(&ima_extend_list_mutex)) {
>   		ret = ima_dump_measurement(&khdr, qe);
>   		if (ret < 0)
>   			break;
>   	}
>   
> +	list_for_each_entry_rcu(qe, &ima_measurements, later,
> +				lockdep_is_held(&ima_extend_list_mutex)) {
> +		if (!ret)
> +			ret = ima_dump_measurement(&khdr, qe);
> +		if (ret < 0)
> +			break;
> +	}
> +
> +	mutex_unlock(&ima_extend_list_mutex);
> +
>   	/*
>   	 * fill in reserved space with some buffer details
>   	 * (eg. version, buffer size, number of measurements)
> @@ -167,6 +180,7 @@ void ima_add_kexec_buffer(struct kimage *image)
>   		extra_memory = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;
>   
>   	binary_runtime_size = ima_get_binary_runtime_size(BINARY) +
> +			      ima_get_binary_runtime_size(BINARY_STAGED) +
>   			      extra_memory;
>   
>   	if (binary_runtime_size >= ULONG_MAX - PAGE_SIZE)
> diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
> index b6d10dceb669..50519ed837d4 100644
> --- a/security/integrity/ima/ima_queue.c
> +++ b/security/integrity/ima/ima_queue.c
> @@ -26,6 +26,7 @@
>   static struct tpm_digest *digests;
>   
>   LIST_HEAD(ima_measurements);	/* list of all measurements */
> +LIST_HEAD(ima_measurements_staged); /* list of staged measurements */
>   #ifdef CONFIG_IMA_KEXEC
>   static unsigned long binary_runtime_size[BINARY__LAST];
>   #else
> @@ -45,11 +46,11 @@ atomic_long_t ima_num_violations = ATOMIC_LONG_INIT(0);
>   /* key: inode (before secure-hashing a file) */
>   struct hlist_head __rcu *ima_htable;
>   
> -/* mutex protects atomicity of extending measurement list
> +/* mutex protects atomicity of extending and staging measurement list
>    * and extending the TPM PCR aggregate. Since tpm_extend can take
>    * long (and the tpm driver uses a mutex), we can't use the spinlock.
>    */
> -static DEFINE_MUTEX(ima_extend_list_mutex);
> +DEFINE_MUTEX(ima_extend_list_mutex);
>   
>   /*
>    * Used internally by the kernel to suspend measurements.
> @@ -174,12 +175,16 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
>   				lockdep_is_held(&ima_extend_list_mutex));
>   
>   	atomic_long_inc(&ima_num_entries[BINARY]);
> +	atomic_long_inc(&ima_num_entries[BINARY_FULL]);
> +
>   	if (update_htable) {
>   		key = ima_hash_key(entry->digests[ima_hash_algo_idx].digest);
>   		hlist_add_head_rcu(&qe->hnext, &htable[key]);
>   	}
>   
>   	ima_update_binary_runtime_size(entry, BINARY);
> +	ima_update_binary_runtime_size(entry, BINARY_FULL);
> +
>   	return 0;
>   }
>   
> @@ -280,6 +285,94 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
>   	return result;
>   }
>   
> +int ima_queue_stage(void)
> +{
> +	int ret = 0;
> +
> +	mutex_lock(&ima_extend_list_mutex);
> +	if (!list_empty(&ima_measurements_staged)) {
> +		ret = -EEXIST;
> +		goto out_unlock;
> +	}
> +
> +	if (list_empty(&ima_measurements)) {
> +		ret = -ENOENT;
> +		goto out_unlock;
> +	}
> +
> +	list_replace(&ima_measurements, &ima_measurements_staged);
> +	INIT_LIST_HEAD(&ima_measurements);
> +
> +	atomic_long_set(&ima_num_entries[BINARY_STAGED],
> +			atomic_long_read(&ima_num_entries[BINARY]));
> +	atomic_long_set(&ima_num_entries[BINARY], 0);
> +
> +	if (IS_ENABLED(CONFIG_IMA_KEXEC)) {
> +		binary_runtime_size[BINARY_STAGED] =
> +					binary_runtime_size[BINARY];
> +		binary_runtime_size[BINARY] = 0;
> +	}
> +out_unlock:
> +	mutex_unlock(&ima_extend_list_mutex);
> +	return ret;
> +}
> +
> +static void ima_queue_delete(struct list_head *head);
> +
> +int ima_queue_staged_delete_all(void)
> +{
> +	LIST_HEAD(ima_measurements_trim);
> +
> +	mutex_lock(&ima_extend_list_mutex);
> +	if (list_empty(&ima_measurements_staged)) {
> +		mutex_unlock(&ima_extend_list_mutex);
> +		return -ENOENT;
> +	}
> +
> +	list_replace(&ima_measurements_staged, &ima_measurements_trim);
> +	INIT_LIST_HEAD(&ima_measurements_staged);
> +
> +	atomic_long_set(&ima_num_entries[BINARY_STAGED], 0);
> +
> +	if (IS_ENABLED(CONFIG_IMA_KEXEC))
> +		binary_runtime_size[BINARY_STAGED] = 0;
> +
> +	mutex_unlock(&ima_extend_list_mutex);
> +
> +	ima_queue_delete(&ima_measurements_trim);
> +	return 0;
> +}
> +
> +static void ima_queue_delete(struct list_head *head)
> +{
> +	struct ima_queue_entry *qe, *qe_tmp;
> +	unsigned int i;
> +
> +	list_for_each_entry_safe(qe, qe_tmp, head, later) {
> +		/*
> +		 * Safe to free template_data here without synchronize_rcu()
> +		 * because the only htable reader, ima_lookup_digest_entry(),
> +		 * accesses only entry->digests, not template_data. If new
> +		 * htable readers are added that access template_data, a
> +		 * synchronize_rcu() is required here.
> +		 */
> +		for (i = 0; i < qe->entry->template_desc->num_fields; i++) {
> +			kfree(qe->entry->template_data[i].data);
> +			qe->entry->template_data[i].data = NULL;
> +			qe->entry->template_data[i].len = 0;
> +		}
> +
> +		list_del(&qe->later);
> +
> +		/* No leak if condition is false, referenced by ima_htable. */
> +		if (IS_ENABLED(CONFIG_IMA_DISABLE_HTABLE)) {
> +			kfree(qe->entry->digests);
> +			kfree(qe->entry);
> +			kfree(qe);
> +		}
> +	}
> +}
> +
>   int ima_restore_measurement_entry(struct ima_template_entry *entry)
>   {
>   	int result = 0;

Re: [PATCH v4 11/13] ima: Support staging and deleting N measurements entries

[steven chen]

On 3/26/2026 10:30 AM, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.com>
>
> Add support for sending a value N between 1 and ULONG_MAX to the staging
> interface. This value represents the number of measurements that should be
> deleted from the current measurements list.
>
> This staging method allows the remote attestation agents to easily separate
> the measurements that were verified (staged and deleted) from those that
> weren't due to the race between taking a TPM quote and reading the
> measurements list.
>
> In order to minimize the locking time of ima_extend_list_mutex, deleting
> N entries is realized by staging the entire current measurements list
> (with the lock), by determining the N-th staged entry (without the lock),
> and by splicing the entries in excess back to the current measurements list
> (with the lock). Finally, the N entries are deleted (without the lock).
>
> Flushing the hash table is not supported for N entries, since it would
> require removing the N entries one by one from the hash table under the
> ima_extend_list_mutex lock, which would increase the locking time.
>
> The ima_extend_list_mutex lock is necessary in ima_dump_measurement_list()
> because ima_queue_staged_delete_partial() uses __list_cut_position() to
> modify ima_measurements_staged, for which no RCU-safe variant exists. For
> the staging with prompt flavor alone, list_replace_rcu() could have been
> used instead, but since both flavors share the same kexec serialization
> path, the mutex is required regardless.
>
> Link: https://github.com/linux-integrity/linux/issues/1
> Suggested-by: Steven Chen <chenste@linux.microsoft.com>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
>   security/integrity/ima/Kconfig     |  3 ++
>   security/integrity/ima/ima.h       |  1 +
>   security/integrity/ima/ima_fs.c    | 22 +++++++++-
>   security/integrity/ima/ima_queue.c | 70 ++++++++++++++++++++++++++++++
>   4 files changed, 95 insertions(+), 1 deletion(-)
>
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index e714726f3384..6ddb4e77bff5 100644
> --- a/security/integrity/ima/Kconfig
> +++ b/security/integrity/ima/Kconfig
> @@ -341,6 +341,9 @@ config IMA_STAGING
>   	  It allows user space to stage the measurements list for deletion and
>   	  to delete the staged measurements after confirmation.
>   
> +	  Or, alternatively, it allows user space to specify N measurements
> +	  entries to be deleted.
> +
>   	  On kexec, staging is reverted and staged measurements are prepended
>   	  to the current measurements list when measurements are copied to the
>   	  secondary kernel.
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 699b735dec7d..de0693fce53c 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -319,6 +319,7 @@ struct ima_template_desc *lookup_template_desc(const char *name);
>   bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
>   int ima_queue_stage(void);
>   int ima_queue_staged_delete_all(void);
> +int ima_queue_staged_delete_partial(unsigned long req_value);
>   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);
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index 39d9128e9f22..eb3f343c1138 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -28,6 +28,7 @@
>    * Requests:
>    * 'A\n': stage the entire measurements list
>    * 'D\n': delete all staged measurements
> + * '[1, ULONG_MAX]\n' delete N measurements entries
>    */
>   #define STAGED_REQ_LENGTH 21
>   
> @@ -319,6 +320,7 @@ static ssize_t ima_measurements_staged_write(struct file *file,
>   					     size_t datalen, loff_t *ppos)
>   {
>   	char req[STAGED_REQ_LENGTH];
> +	unsigned long req_value;
>   	int ret;
>   
>   	if (*ppos > 0 || datalen < 2 || datalen > STAGED_REQ_LENGTH)
> @@ -346,7 +348,25 @@ static ssize_t ima_measurements_staged_write(struct file *file,
>   		ret = ima_queue_staged_delete_all();
>   		break;
>   	default:
> -		ret = -EINVAL;
> +		if (ima_flush_htable) {
> +			pr_debug("Deleting staged N measurements not supported when flushing the hash table is requested\n");
> +			return -EINVAL;
> +		}
> +
> +		ret = kstrtoul(req, 10, &req_value);
> +		if (ret < 0)
> +			return ret;
> +
> +		if (req_value == 0) {
> +			pr_debug("Must delete at least one entry\n");
> +			return -EINVAL;
> +		}
> +
> +		ret = ima_queue_stage();
> +		if (ret < 0)
> +			return ret;
> +
> +		ret = ima_queue_staged_delete_partial(req_value);
The default processing is "Trim N" idea plus performance improvement.

Here do everything in one time. And this is what I said in v3.

[PATCH v3 1/3] ima: Remove ima_h_table structure 
<https://lore.kernel.org/linux-integrity/c61aeaa79929a98cb3a6d30835972891fac3570f.camel@linux.ibm.com/T/#t>


The important two parts of trimming is "trim N" and performance improvement.

The performance improvement include two parts:
     hash table staging
     active log list staging

And I think "Trim N" plus performance improvement is the right direction 
to go.
Lots of code for two steps "stage and trim" "stage" part can be removed.

Also race condition may happen if not holding the list all time in user 
space
during attestation period: from stage, read list, attestation and trimming.

So in order to improve the above user space lock time, "Trim T:N" can be 
used
not to hold list long in user space during attestation.

For Trim T:N, T represent total log trimmed since system boot up. Please 
refer to
https://lore.kernel.org/linux-integrity/20260205235849.7086-1-chenste@linux.microsoft.com/T/#t

Thanks,

Steven
>   	}
>   
>   	if (ret < 0)
> diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
> index f5c18acfbc43..4fb557d61a88 100644
> --- a/security/integrity/ima/ima_queue.c
> +++ b/security/integrity/ima/ima_queue.c
> @@ -371,6 +371,76 @@ int ima_queue_staged_delete_all(void)
>   	return 0;
>   }
>   
> +int ima_queue_staged_delete_partial(unsigned long req_value)
> +{
> +	unsigned long req_value_copy = req_value;
> +	unsigned long size_to_remove = 0, num_to_remove = 0;
> +	struct list_head *cut_pos = NULL;
> +	LIST_HEAD(ima_measurements_trim);
> +	struct ima_queue_entry *qe;
> +	int ret = 0;
> +
> +	/*
> +	 * Safe walk (no concurrent write), not under ima_extend_list_mutex
> +	 * for performance reasons.
> +	 */
> +	list_for_each_entry(qe, &ima_measurements_staged, later) {
> +		size_to_remove += get_binary_runtime_size(qe->entry);
> +		num_to_remove++;
> +
> +		if (--req_value_copy == 0) {
> +			/* qe->later always points to a valid list entry. */
> +			cut_pos = &qe->later;
> +			break;
> +		}
> +	}
> +
> +	/* Nothing to remove, undoing staging. */
> +	if (req_value_copy > 0) {
> +		size_to_remove = 0;
> +		num_to_remove = 0;
> +		ret = -ENOENT;
> +	}
> +
> +	mutex_lock(&ima_extend_list_mutex);
> +	if (list_empty(&ima_measurements_staged)) {
> +		mutex_unlock(&ima_extend_list_mutex);
> +		return -ENOENT;
> +	}
> +
> +	if (cut_pos != NULL)
> +		/*
> +		 * ima_dump_measurement_list() does not modify the list,
> +		 * cut_pos remains the same even if it was computed before
> +		 * the lock.
> +		 */
> +		__list_cut_position(&ima_measurements_trim,
> +				    &ima_measurements_staged, cut_pos);
> +
> +	atomic_long_sub(num_to_remove, &ima_num_entries[BINARY_STAGED]);
> +	atomic_long_add(atomic_long_read(&ima_num_entries[BINARY_STAGED]),
> +			&ima_num_entries[BINARY]);
> +	atomic_long_set(&ima_num_entries[BINARY_STAGED], 0);
> +
> +	if (IS_ENABLED(CONFIG_IMA_KEXEC)) {
> +		binary_runtime_size[BINARY_STAGED] -= size_to_remove;
> +		binary_runtime_size[BINARY] +=
> +					binary_runtime_size[BINARY_STAGED];
> +		binary_runtime_size[BINARY_STAGED] = 0;
> +	}
> +
> +	/*
> +	 * Splice (prepend) any remaining non-deleted staged entries to the
> +	 * active list (RCU not needed, there cannot be concurrent readers).
> +	 */
> +	list_splice(&ima_measurements_staged, &ima_measurements);
> +	INIT_LIST_HEAD(&ima_measurements_staged);
> +	mutex_unlock(&ima_extend_list_mutex);
> +
> +	ima_queue_delete(&ima_measurements_trim, false);
> +	return ret;
> +}
> +
>   static void ima_queue_delete(struct list_head *head, bool flush_htable)
>   {
>   	struct ima_queue_entry *qe, *qe_tmp;

Re: [PATCH v4 09/13] ima: Add support for staging measurements with prompt

[Roberto Sassu]

On Thu, 2026-03-26 at 15:44 -0700, steven chen wrote:
> On 3/26/2026 10:30 AM, Roberto Sassu wrote:
> > From: Roberto Sassu <roberto.sassu@huawei.com>
> > 
> > Introduce the ability of staging the IMA measurement list and deleting them
> > with a prompt.
> > 
> > Staging means moving the current content of the measurement list to a
> > separate location, and allowing users to read and delete it. This causes
> > the measurement list to be atomically truncated before new measurements can
> > be added. Staging can be done only once at a time. In the event of kexec(),
> > staging is reverted and staged entries will be carried over to the new
> > kernel.
> > 
> > Introduce ascii_runtime_measurements_<algo>_staged and
> > binary_runtime_measurements_<algo>_staged interfaces to stage and delete
> > the measurements. Use 'echo A > <IMA interface>' and
> > 'echo D > <IMA interface>' to respectively stage and delete the entire
> > measurements list. Locking of these interfaces is also mediated with a call
> > to _ima_measurements_open() and with ima_measurements_release().
> > 
> > Implement the staging functionality by introducing the new global
> > measurements list ima_measurements_staged, and ima_queue_stage() and
> > ima_queue_delete_staged_all() to respectively move measurements from the
> > current measurements list to the staged one, and to move staged
> > measurements to the ima_measurements_trim list for deletion. Introduce
> > ima_queue_delete() to delete the measurements.
> > 
> > Finally, introduce the BINARY_STAGED AND BINARY_FULL binary measurements
> > list types, to maintain the counters and the binary size of staged
> > measurements and the full measurements list (including entries that were
> > staged). BINARY still represents the current binary measurements list.
> > 
> > Use the binary size for the BINARY + BINARY_STAGED types in
> > ima_add_kexec_buffer(), since both measurements list types are copied to
> > the secondary kernel during kexec. Use BINARY_FULL in
> > ima_measure_kexec_event(), to generate a critical data record.
> > 
> > It should be noted that the BINARY_FULL counter is not passed through
> > kexec. Thus, the number of entries included in the kexec critical data
> > records refers to the entries since the previous kexec records.
> > 
> > Note: This code derives from the Alt-IMA Huawei project, whose license is
> >        GPL-2.0 OR MIT.
> > 
> > Link: https://github.com/linux-integrity/linux/issues/1
> > Suggested-by: Gregory Lumen <gregorylumen@linux.microsoft.com> (staging revert)
> > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > ---
> >   security/integrity/ima/Kconfig     |  13 +++
> >   security/integrity/ima/ima.h       |   8 +-
> >   security/integrity/ima/ima_fs.c    | 167 ++++++++++++++++++++++++++---
> >   security/integrity/ima/ima_kexec.c |  22 +++-
> >   security/integrity/ima/ima_queue.c |  97 ++++++++++++++++-
> >   5 files changed, 286 insertions(+), 21 deletions(-)
> > 
> > diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> > index 976e75f9b9ba..e714726f3384 100644
> > --- a/security/integrity/ima/Kconfig
> > +++ b/security/integrity/ima/Kconfig
> > @@ -332,4 +332,17 @@ config IMA_KEXEC_EXTRA_MEMORY_KB
> >   	  If set to the default value of 0, an extra half page of memory for those
> >   	  additional measurements will be allocated.
> >   
> > +config IMA_STAGING
> > +	bool "Support for staging the measurements list"
> > +	default y
> > +	help
> > +	  Add support for staging the measurements list.
> > +
> > +	  It allows user space to stage the measurements list for deletion and
> > +	  to delete the staged measurements after confirmation.
> > +
> > +	  On kexec, staging is reverted and staged measurements are prepended
> > +	  to the current measurements list when measurements are copied to the
> > +	  secondary kernel.
> > +
> >   endif
> > diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> > index 97b7d6024b5d..65db152a0a24 100644
> > --- a/security/integrity/ima/ima.h
> > +++ b/security/integrity/ima/ima.h
> > @@ -30,9 +30,11 @@ enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8, TPM_PCR10 = 10 };
> >   
> >   /*
> >    * BINARY: current binary measurements list
> > + * BINARY_STAGED: staged binary measurements list
> > + * BINARY_FULL: binary measurements list since IMA init (lost after kexec)
> >    */
> >   enum binary_lists {
> > -	BINARY, BINARY__LAST
> > +	BINARY, BINARY_STAGED, BINARY_FULL, BINARY__LAST
> >   };
> >   
> >   /* digest size for IMA, fits SHA1 or MD5 */
> > @@ -125,6 +127,7 @@ struct ima_queue_entry {
> >   	struct ima_template_entry *entry;
> >   };
> >   extern struct list_head ima_measurements;	/* list of all measurements */
> > +extern struct list_head ima_measurements_staged; /* list of staged meas. */
> >   
> >   /* Some details preceding the binary serialized measurement list */
> >   struct ima_kexec_hdr {
> > @@ -314,6 +317,8 @@ struct ima_template_desc *ima_template_desc_current(void);
> >   struct ima_template_desc *ima_template_desc_buf(void);
> >   struct ima_template_desc *lookup_template_desc(const char *name);
> >   bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
> > +int ima_queue_stage(void);
> > +int ima_queue_staged_delete_all(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);
> > @@ -334,6 +339,7 @@ extern spinlock_t ima_queue_lock;
> >   extern atomic_long_t ima_num_entries[BINARY__LAST];
> >   extern atomic_long_t ima_num_violations;
> >   extern struct hlist_head __rcu *ima_htable;
> > +extern struct mutex ima_extend_list_mutex;
> >   
> >   static inline unsigned int ima_hash_key(u8 *digest)
> >   {
> > diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> > index 7709a4576322..39d9128e9f22 100644
> > --- a/security/integrity/ima/ima_fs.c
> > +++ b/security/integrity/ima/ima_fs.c
> > @@ -24,6 +24,13 @@
> >   
> >   #include "ima.h"
> >   
> > +/*
> > + * Requests:
> > + * 'A\n': stage the entire measurements list
> > + * 'D\n': delete all staged measurements
> > + */
> > +#define STAGED_REQ_LENGTH 21
> > +
> >   static DEFINE_MUTEX(ima_write_mutex);
> >   static DEFINE_MUTEX(ima_measure_mutex);
> >   static long ima_measure_users;
> > @@ -97,6 +104,11 @@ static void *ima_measurements_start(struct seq_file *m, loff_t *pos)
> >   	return _ima_measurements_start(m, pos, &ima_measurements);
> >   }
> >   
> > +static void *ima_measurements_staged_start(struct seq_file *m, loff_t *pos)
> > +{
> > +	return _ima_measurements_start(m, pos, &ima_measurements_staged);
> > +}
> > +
> >   static void *_ima_measurements_next(struct seq_file *m, void *v, loff_t *pos,
> >   				    struct list_head *head)
> >   {
> > @@ -118,6 +130,12 @@ static void *ima_measurements_next(struct seq_file *m, void *v, loff_t *pos)
> >   	return _ima_measurements_next(m, v, pos, &ima_measurements);
> >   }
> >   
> > +static void *ima_measurements_staged_next(struct seq_file *m, void *v,
> > +					  loff_t *pos)
> > +{
> > +	return _ima_measurements_next(m, v, pos, &ima_measurements_staged);
> > +}
> > +
> >   static void ima_measurements_stop(struct seq_file *m, void *v)
> >   {
> >   }
> > @@ -283,6 +301,68 @@ static const struct file_operations ima_measurements_ops = {
> >   	.release = ima_measurements_release,
> >   };
> >   
> > +static const struct seq_operations ima_measurments_staged_seqops = {
> > +	.start = ima_measurements_staged_start,
> > +	.next = ima_measurements_staged_next,
> > +	.stop = ima_measurements_stop,
> > +	.show = ima_measurements_show
> > +};
> > +
> > +static int ima_measurements_staged_open(struct inode *inode, struct file *file)
> > +{
> > +	return _ima_measurements_open(inode, file,
> > +				      &ima_measurments_staged_seqops);
> > +}
> > +
> > +static ssize_t ima_measurements_staged_write(struct file *file,
> > +					     const char __user *buf,
> > +					     size_t datalen, loff_t *ppos)
> > +{
> > +	char req[STAGED_REQ_LENGTH];
> > +	int ret;
> > +
> > +	if (*ppos > 0 || datalen < 2 || datalen > STAGED_REQ_LENGTH)
> > +		return -EINVAL;
> > +
> > +	if (copy_from_user(req, buf, datalen) != 0)
> > +		return -EFAULT;
> > +
> > +	if (req[datalen - 1] != '\n')
> > +		return -EINVAL;
> > +
> > +	req[datalen - 1] = '\0';
> > +
> > +	switch (req[0]) {
> > +	case 'A':
> > +		if (datalen != 2)
> > +			return -EINVAL;
> > +
> > +		ret = ima_queue_stage();
> > +		break;
> > +	case 'D':
> > +		if (datalen != 2)
> > +			return -EINVAL;
> > +
> > +		ret = ima_queue_staged_delete_all();
> > +		break;
> 
> I think the following two steps may not work because of race condition:
> 
> step1: ret = ima_queue_stage(); //this will put all logs in active list into staged list;
> step2: ret = ima_queue_staged_delete_all(); //this will delete all logs in staged list;
> 
> The following is the step of race condition:
>      1. current active log list LA1;
>      2. user agent read the TPM quote QA1 match list LA1;
>      3. new event NewLog is added into active log list LA1+NewLog
>      4. user agent call ima_queue_stage() and generated staged list
>         including LA1+NewLog.
>      5. user agent call ima_queue_staged_delete_all();
>         The new log NewLog in step 3 is also deleted

Please refer to the documentation patch which explains the intended
workflow of this approach (Remote Attestation Agent Workflow).

Roberto

> Next time the attestation will fail if using the active log list in the 
> kernel.
> 
> Thanks,
> 
> Steven
> 
> > +	default:
> > +		ret = -EINVAL;
> > +	}
> > +
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	return datalen;
> > +}
> > +
> > +static const struct file_operations ima_measurements_staged_ops = {
> > +	.open = ima_measurements_staged_open,
> > +	.read = seq_read,
> > +	.write = ima_measurements_staged_write,
> > +	.llseek = seq_lseek,
> > +	.release = ima_measurements_release,
> > +};
> > +
> >   void ima_print_digest(struct seq_file *m, u8 *digest, u32 size)
> >   {
> >   	u32 i;
> > @@ -356,6 +436,28 @@ static const struct file_operations ima_ascii_measurements_ops = {
> >   	.release = ima_measurements_release,
> >   };
> >   
> > +static const struct seq_operations ima_ascii_measurements_staged_seqops = {
> > +	.start = ima_measurements_staged_start,
> > +	.next = ima_measurements_staged_next,
> > +	.stop = ima_measurements_stop,
> > +	.show = ima_ascii_measurements_show
> > +};
> > +
> > +static int ima_ascii_measurements_staged_open(struct inode *inode,
> > +					      struct file *file)
> > +{
> > +	return _ima_measurements_open(inode, file,
> > +				      &ima_ascii_measurements_staged_seqops);
> > +}
> > +
> > +static const struct file_operations ima_ascii_measurements_staged_ops = {
> > +	.open = ima_ascii_measurements_staged_open,
> > +	.read = seq_read,
> > +	.write = ima_measurements_staged_write,
> > +	.llseek = seq_lseek,
> > +	.release = ima_measurements_release,
> > +};
> > +
> >   static ssize_t ima_read_policy(char *path)
> >   {
> >   	void *data = NULL;
> > @@ -459,10 +561,21 @@ static const struct seq_operations ima_policy_seqops = {
> >   };
> >   #endif
> >   
> > -static int __init create_securityfs_measurement_lists(void)
> > +static int __init create_securityfs_measurement_lists(bool staging)
> >   {
> > +	const struct file_operations *ascii_ops = &ima_ascii_measurements_ops;
> > +	const struct file_operations *binary_ops = &ima_measurements_ops;
> > +	mode_t permissions = S_IRUSR | S_IRGRP;
> > +	const char *file_suffix = "";
> >   	int count = NR_BANKS(ima_tpm_chip);
> >   
> > +	if (staging) {
> > +		ascii_ops = &ima_ascii_measurements_staged_ops;
> > +		binary_ops = &ima_measurements_staged_ops;
> > +		file_suffix = "_staged";
> > +		permissions |= (S_IWUSR | S_IWGRP);
> > +	}
> > +
> >   	if (ima_sha1_idx >= NR_BANKS(ima_tpm_chip))
> >   		count++;
> >   
> > @@ -473,29 +586,32 @@ static int __init create_securityfs_measurement_lists(void)
> >   
> >   		if (algo == HASH_ALGO__LAST)
> >   			snprintf(file_name, sizeof(file_name),
> > -				 "ascii_runtime_measurements_tpm_alg_%x",
> > -				 ima_tpm_chip->allocated_banks[i].alg_id);
> > +				 "ascii_runtime_measurements_tpm_alg_%x%s",
> > +				 ima_tpm_chip->allocated_banks[i].alg_id,
> > +				 file_suffix);
> >   		else
> >   			snprintf(file_name, sizeof(file_name),
> > -				 "ascii_runtime_measurements_%s",
> > -				 hash_algo_name[algo]);
> > -		dentry = securityfs_create_file(file_name, S_IRUSR | S_IRGRP,
> > +				 "ascii_runtime_measurements_%s%s",
> > +				 hash_algo_name[algo], file_suffix);
> > +		dentry = securityfs_create_file(file_name, permissions,
> >   						ima_dir, (void *)(uintptr_t)i,
> > -						&ima_ascii_measurements_ops);
> > +						ascii_ops);
> >   		if (IS_ERR(dentry))
> >   			return PTR_ERR(dentry);
> >   
> >   		if (algo == HASH_ALGO__LAST)
> >   			snprintf(file_name, sizeof(file_name),
> > -				 "binary_runtime_measurements_tpm_alg_%x",
> > -				 ima_tpm_chip->allocated_banks[i].alg_id);
> > +				 "binary_runtime_measurements_tpm_alg_%x%s",
> > +				 ima_tpm_chip->allocated_banks[i].alg_id,
> > +				 file_suffix);
> >   		else
> >   			snprintf(file_name, sizeof(file_name),
> > -				 "binary_runtime_measurements_%s",
> > -				 hash_algo_name[algo]);
> > -		dentry = securityfs_create_file(file_name, S_IRUSR | S_IRGRP,
> > +				 "binary_runtime_measurements_%s%s",
> > +				 hash_algo_name[algo], file_suffix);
> > +
> > +		dentry = securityfs_create_file(file_name, permissions,
> >   						ima_dir, (void *)(uintptr_t)i,
> > -						&ima_measurements_ops);
> > +						binary_ops);
> >   		if (IS_ERR(dentry))
> >   			return PTR_ERR(dentry);
> >   	}
> > @@ -503,6 +619,23 @@ static int __init create_securityfs_measurement_lists(void)
> >   	return 0;
> >   }
> >   
> > +static int __init create_securityfs_staging_links(void)
> > +{
> > +	struct dentry *dentry;
> > +
> > +	dentry = securityfs_create_symlink("binary_runtime_measurements_staged",
> > +		ima_dir, "binary_runtime_measurements_sha1_staged", NULL);
> > +	if (IS_ERR(dentry))
> > +		return PTR_ERR(dentry);
> > +
> > +	dentry = securityfs_create_symlink("ascii_runtime_measurements_staged",
> > +		ima_dir, "ascii_runtime_measurements_sha1_staged", NULL);
> > +	if (IS_ERR(dentry))
> > +		return PTR_ERR(dentry);
> > +
> > +	return 0;
> > +}
> > +
> >   /*
> >    * ima_open_policy: sequentialize access to the policy file
> >    */
> > @@ -595,7 +728,13 @@ int __init ima_fs_init(void)
> >   		goto out;
> >   	}
> >   
> > -	ret = create_securityfs_measurement_lists();
> > +	ret = create_securityfs_measurement_lists(false);
> > +	if (ret == 0 && IS_ENABLED(CONFIG_IMA_STAGING)) {
> > +		ret = create_securityfs_measurement_lists(true);
> > +		if (ret == 0)
> > +			ret = create_securityfs_staging_links();
> > +	}
> > +
> >   	if (ret != 0)
> >   		goto out;
> >   
> > diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> > index d7d0fb639d99..d5503dd5cc9b 100644
> > --- a/security/integrity/ima/ima_kexec.c
> > +++ b/security/integrity/ima/ima_kexec.c
> > @@ -42,8 +42,8 @@ void ima_measure_kexec_event(const char *event_name)
> >   	long len;
> >   	int n;
> >   
> > -	buf_size = ima_get_binary_runtime_size(BINARY);
> > -	len = atomic_long_read(&ima_num_entries[BINARY]);
> > +	buf_size = ima_get_binary_runtime_size(BINARY_FULL);
> > +	len = atomic_long_read(&ima_num_entries[BINARY_FULL]);
> >   
> >   	n = scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
> >   		      "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;"
> > @@ -106,13 +106,26 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
> >   
> >   	memset(&khdr, 0, sizeof(khdr));
> >   	khdr.version = 1;
> > -	/* This is an append-only list, no need to hold the RCU read lock */
> > -	list_for_each_entry_rcu(qe, &ima_measurements, later, true) {
> > +	/* It can race with ima_queue_stage() and ima_queue_delete_staged(). */
> > +	mutex_lock(&ima_extend_list_mutex);
> > +
> > +	list_for_each_entry_rcu(qe, &ima_measurements_staged, later,
> > +				lockdep_is_held(&ima_extend_list_mutex)) {
> >   		ret = ima_dump_measurement(&khdr, qe);
> >   		if (ret < 0)
> >   			break;
> >   	}
> >   
> > +	list_for_each_entry_rcu(qe, &ima_measurements, later,
> > +				lockdep_is_held(&ima_extend_list_mutex)) {
> > +		if (!ret)
> > +			ret = ima_dump_measurement(&khdr, qe);
> > +		if (ret < 0)
> > +			break;
> > +	}
> > +
> > +	mutex_unlock(&ima_extend_list_mutex);
> > +
> >   	/*
> >   	 * fill in reserved space with some buffer details
> >   	 * (eg. version, buffer size, number of measurements)
> > @@ -167,6 +180,7 @@ void ima_add_kexec_buffer(struct kimage *image)
> >   		extra_memory = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;
> >   
> >   	binary_runtime_size = ima_get_binary_runtime_size(BINARY) +
> > +			      ima_get_binary_runtime_size(BINARY_STAGED) +
> >   			      extra_memory;
> >   
> >   	if (binary_runtime_size >= ULONG_MAX - PAGE_SIZE)
> > diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
> > index b6d10dceb669..50519ed837d4 100644
> > --- a/security/integrity/ima/ima_queue.c
> > +++ b/security/integrity/ima/ima_queue.c
> > @@ -26,6 +26,7 @@
> >   static struct tpm_digest *digests;
> >   
> >   LIST_HEAD(ima_measurements);	/* list of all measurements */
> > +LIST_HEAD(ima_measurements_staged); /* list of staged measurements */
> >   #ifdef CONFIG_IMA_KEXEC
> >   static unsigned long binary_runtime_size[BINARY__LAST];
> >   #else
> > @@ -45,11 +46,11 @@ atomic_long_t ima_num_violations = ATOMIC_LONG_INIT(0);
> >   /* key: inode (before secure-hashing a file) */
> >   struct hlist_head __rcu *ima_htable;
> >   
> > -/* mutex protects atomicity of extending measurement list
> > +/* mutex protects atomicity of extending and staging measurement list
> >    * and extending the TPM PCR aggregate. Since tpm_extend can take
> >    * long (and the tpm driver uses a mutex), we can't use the spinlock.
> >    */
> > -static DEFINE_MUTEX(ima_extend_list_mutex);
> > +DEFINE_MUTEX(ima_extend_list_mutex);
> >   
> >   /*
> >    * Used internally by the kernel to suspend measurements.
> > @@ -174,12 +175,16 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
> >   				lockdep_is_held(&ima_extend_list_mutex));
> >   
> >   	atomic_long_inc(&ima_num_entries[BINARY]);
> > +	atomic_long_inc(&ima_num_entries[BINARY_FULL]);
> > +
> >   	if (update_htable) {
> >   		key = ima_hash_key(entry->digests[ima_hash_algo_idx].digest);
> >   		hlist_add_head_rcu(&qe->hnext, &htable[key]);
> >   	}
> >   
> >   	ima_update_binary_runtime_size(entry, BINARY);
> > +	ima_update_binary_runtime_size(entry, BINARY_FULL);
> > +
> >   	return 0;
> >   }
> >   
> > @@ -280,6 +285,94 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
> >   	return result;
> >   }
> >   
> > +int ima_queue_stage(void)
> > +{
> > +	int ret = 0;
> > +
> > +	mutex_lock(&ima_extend_list_mutex);
> > +	if (!list_empty(&ima_measurements_staged)) {
> > +		ret = -EEXIST;
> > +		goto out_unlock;
> > +	}
> > +
> > +	if (list_empty(&ima_measurements)) {
> > +		ret = -ENOENT;
> > +		goto out_unlock;
> > +	}
> > +
> > +	list_replace(&ima_measurements, &ima_measurements_staged);
> > +	INIT_LIST_HEAD(&ima_measurements);
> > +
> > +	atomic_long_set(&ima_num_entries[BINARY_STAGED],
> > +			atomic_long_read(&ima_num_entries[BINARY]));
> > +	atomic_long_set(&ima_num_entries[BINARY], 0);
> > +
> > +	if (IS_ENABLED(CONFIG_IMA_KEXEC)) {
> > +		binary_runtime_size[BINARY_STAGED] =
> > +					binary_runtime_size[BINARY];
> > +		binary_runtime_size[BINARY] = 0;
> > +	}
> > +out_unlock:
> > +	mutex_unlock(&ima_extend_list_mutex);
> > +	return ret;
> > +}
> > +
> > +static void ima_queue_delete(struct list_head *head);
> > +
> > +int ima_queue_staged_delete_all(void)
> > +{
> > +	LIST_HEAD(ima_measurements_trim);
> > +
> > +	mutex_lock(&ima_extend_list_mutex);
> > +	if (list_empty(&ima_measurements_staged)) {
> > +		mutex_unlock(&ima_extend_list_mutex);
> > +		return -ENOENT;
> > +	}
> > +
> > +	list_replace(&ima_measurements_staged, &ima_measurements_trim);
> > +	INIT_LIST_HEAD(&ima_measurements_staged);
> > +
> > +	atomic_long_set(&ima_num_entries[BINARY_STAGED], 0);
> > +
> > +	if (IS_ENABLED(CONFIG_IMA_KEXEC))
> > +		binary_runtime_size[BINARY_STAGED] = 0;
> > +
> > +	mutex_unlock(&ima_extend_list_mutex);
> > +
> > +	ima_queue_delete(&ima_measurements_trim);
> > +	return 0;
> > +}
> > +
> > +static void ima_queue_delete(struct list_head *head)
> > +{
> > +	struct ima_queue_entry *qe, *qe_tmp;
> > +	unsigned int i;
> > +
> > +	list_for_each_entry_safe(qe, qe_tmp, head, later) {
> > +		/*
> > +		 * Safe to free template_data here without synchronize_rcu()
> > +		 * because the only htable reader, ima_lookup_digest_entry(),
> > +		 * accesses only entry->digests, not template_data. If new
> > +		 * htable readers are added that access template_data, a
> > +		 * synchronize_rcu() is required here.
> > +		 */
> > +		for (i = 0; i < qe->entry->template_desc->num_fields; i++) {
> > +			kfree(qe->entry->template_data[i].data);
> > +			qe->entry->template_data[i].data = NULL;
> > +			qe->entry->template_data[i].len = 0;
> > +		}
> > +
> > +		list_del(&qe->later);
> > +
> > +		/* No leak if condition is false, referenced by ima_htable. */
> > +		if (IS_ENABLED(CONFIG_IMA_DISABLE_HTABLE)) {
> > +			kfree(qe->entry->digests);
> > +			kfree(qe->entry);
> > +			kfree(qe);
> > +		}
> > +	}
> > +}
> > +
> >   int ima_restore_measurement_entry(struct ima_template_entry *entry)
> >   {
> >   	int result = 0;
> 

Re: [PATCH v4 11/13] ima: Support staging and deleting N measurements entries

[Roberto Sassu]

On Thu, 2026-03-26 at 16:19 -0700, steven chen wrote:
> On 3/26/2026 10:30 AM, Roberto Sassu wrote:
> > From: Roberto Sassu <roberto.sassu@huawei.com>
> > 
> > Add support for sending a value N between 1 and ULONG_MAX to the staging
> > interface. This value represents the number of measurements that should be
> > deleted from the current measurements list.
> > 
> > This staging method allows the remote attestation agents to easily separate
> > the measurements that were verified (staged and deleted) from those that
> > weren't due to the race between taking a TPM quote and reading the
> > measurements list.
> > 
> > In order to minimize the locking time of ima_extend_list_mutex, deleting
> > N entries is realized by staging the entire current measurements list
> > (with the lock), by determining the N-th staged entry (without the lock),
> > and by splicing the entries in excess back to the current measurements list
> > (with the lock). Finally, the N entries are deleted (without the lock).
> > 
> > Flushing the hash table is not supported for N entries, since it would
> > require removing the N entries one by one from the hash table under the
> > ima_extend_list_mutex lock, which would increase the locking time.
> > 
> > The ima_extend_list_mutex lock is necessary in ima_dump_measurement_list()
> > because ima_queue_staged_delete_partial() uses __list_cut_position() to
> > modify ima_measurements_staged, for which no RCU-safe variant exists. For
> > the staging with prompt flavor alone, list_replace_rcu() could have been
> > used instead, but since both flavors share the same kexec serialization
> > path, the mutex is required regardless.
> > 
> > Link: https://github.com/linux-integrity/linux/issues/1
> > Suggested-by: Steven Chen <chenste@linux.microsoft.com>
> > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > ---
> >   security/integrity/ima/Kconfig     |  3 ++
> >   security/integrity/ima/ima.h       |  1 +
> >   security/integrity/ima/ima_fs.c    | 22 +++++++++-
> >   security/integrity/ima/ima_queue.c | 70 ++++++++++++++++++++++++++++++
> >   4 files changed, 95 insertions(+), 1 deletion(-)
> > 
> > diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> > index e714726f3384..6ddb4e77bff5 100644
> > --- a/security/integrity/ima/Kconfig
> > +++ b/security/integrity/ima/Kconfig
> > @@ -341,6 +341,9 @@ config IMA_STAGING
> >   	  It allows user space to stage the measurements list for deletion and
> >   	  to delete the staged measurements after confirmation.
> >   
> > +	  Or, alternatively, it allows user space to specify N measurements
> > +	  entries to be deleted.
> > +
> >   	  On kexec, staging is reverted and staged measurements are prepended
> >   	  to the current measurements list when measurements are copied to the
> >   	  secondary kernel.
> > diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> > index 699b735dec7d..de0693fce53c 100644
> > --- a/security/integrity/ima/ima.h
> > +++ b/security/integrity/ima/ima.h
> > @@ -319,6 +319,7 @@ struct ima_template_desc *lookup_template_desc(const char *name);
> >   bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
> >   int ima_queue_stage(void);
> >   int ima_queue_staged_delete_all(void);
> > +int ima_queue_staged_delete_partial(unsigned long req_value);
> >   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);
> > diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> > index 39d9128e9f22..eb3f343c1138 100644
> > --- a/security/integrity/ima/ima_fs.c
> > +++ b/security/integrity/ima/ima_fs.c
> > @@ -28,6 +28,7 @@
> >    * Requests:
> >    * 'A\n': stage the entire measurements list
> >    * 'D\n': delete all staged measurements
> > + * '[1, ULONG_MAX]\n' delete N measurements entries
> >    */
> >   #define STAGED_REQ_LENGTH 21
> >   
> > @@ -319,6 +320,7 @@ static ssize_t ima_measurements_staged_write(struct file *file,
> >   					     size_t datalen, loff_t *ppos)
> >   {
> >   	char req[STAGED_REQ_LENGTH];
> > +	unsigned long req_value;
> >   	int ret;
> >   
> >   	if (*ppos > 0 || datalen < 2 || datalen > STAGED_REQ_LENGTH)
> > @@ -346,7 +348,25 @@ static ssize_t ima_measurements_staged_write(struct file *file,
> >   		ret = ima_queue_staged_delete_all();
> >   		break;
> >   	default:
> > -		ret = -EINVAL;
> > +		if (ima_flush_htable) {
> > +			pr_debug("Deleting staged N measurements not supported when flushing the hash table is requested\n");
> > +			return -EINVAL;
> > +		}
> > +
> > +		ret = kstrtoul(req, 10, &req_value);
> > +		if (ret < 0)
> > +			return ret;
> > +
> > +		if (req_value == 0) {
> > +			pr_debug("Must delete at least one entry\n");
> > +			return -EINVAL;
> > +		}
> > +
> > +		ret = ima_queue_stage();
> > +		if (ret < 0)
> > +			return ret;
> > +
> > +		ret = ima_queue_staged_delete_partial(req_value);
> The default processing is "Trim N" idea plus performance improvement.
> 
> Here do everything in one time. And this is what I said in v3.
> 
> [PATCH v3 1/3] ima: Remove ima_h_table structure 
> <https://lore.kernel.org/linux-integrity/c61aeaa79929a98cb3a6d30835972891fac3570f.camel@linux.ibm.com/T/#t>

In your approach you do:

lock ima_extend_measure_list_mutex
scan entries until N
cut list staged -> trim
unlock ima_extend_measure_list_mutex


In my approach I do:
lock ima_extend_measure_list_mutex
list replace active -> staged
unlock ima_extend_measure_list_mutex

scan entries until N

lock ima_extend_measure_list_mutex
cut list staged -> trim
splice staged ->active
unlock ima_extend_measure_list_mutex

So, I guess if you refer to less user space locking time, you mean one
lock/unlock and one list replace + list splice less in your solution.

In exchange, you propose to hold the lock in the kernel while scanning
N. I think it is a significant increase of kernel locking time vs a
negligible increase of user space locking time (in the kernel, all
processes need to wait for the ima_extend_measure_list_mutex to be
released, in user space it is just the agent waiting).

Roberto

> The important two parts of trimming is "trim N" and performance improvement.
> 
> The performance improvement include two parts:
>      hash table staging
>      active log list staging
> 
> And I think "Trim N" plus performance improvement is the right direction 
> to go.
> Lots of code for two steps "stage and trim" "stage" part can be removed.
> 
> Also race condition may happen if not holding the list all time in user 
> space
> during attestation period: from stage, read list, attestation and trimming.
> 
> So in order to improve the above user space lock time, "Trim T:N" can be 
> used
> not to hold list long in user space during attestation.
> 
> For Trim T:N, T represent total log trimmed since system boot up. Please 
> refer to
> https://lore.kernel.org/linux-integrity/20260205235849.7086-1-chenste@linux.microsoft.com/T/#t
> 
> Thanks,
> 
> Steven
> >   	}
> >   
> >   	if (ret < 0)
> > diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
> > index f5c18acfbc43..4fb557d61a88 100644
> > --- a/security/integrity/ima/ima_queue.c
> > +++ b/security/integrity/ima/ima_queue.c
> > @@ -371,6 +371,76 @@ int ima_queue_staged_delete_all(void)
> >   	return 0;
> >   }
> >   
> > +int ima_queue_staged_delete_partial(unsigned long req_value)
> > +{
> > +	unsigned long req_value_copy = req_value;
> > +	unsigned long size_to_remove = 0, num_to_remove = 0;
> > +	struct list_head *cut_pos = NULL;
> > +	LIST_HEAD(ima_measurements_trim);
> > +	struct ima_queue_entry *qe;
> > +	int ret = 0;
> > +
> > +	/*
> > +	 * Safe walk (no concurrent write), not under ima_extend_list_mutex
> > +	 * for performance reasons.
> > +	 */
> > +	list_for_each_entry(qe, &ima_measurements_staged, later) {
> > +		size_to_remove += get_binary_runtime_size(qe->entry);
> > +		num_to_remove++;
> > +
> > +		if (--req_value_copy == 0) {
> > +			/* qe->later always points to a valid list entry. */
> > +			cut_pos = &qe->later;
> > +			break;
> > +		}
> > +	}
> > +
> > +	/* Nothing to remove, undoing staging. */
> > +	if (req_value_copy > 0) {
> > +		size_to_remove = 0;
> > +		num_to_remove = 0;
> > +		ret = -ENOENT;
> > +	}
> > +
> > +	mutex_lock(&ima_extend_list_mutex);
> > +	if (list_empty(&ima_measurements_staged)) {
> > +		mutex_unlock(&ima_extend_list_mutex);
> > +		return -ENOENT;
> > +	}
> > +
> > +	if (cut_pos != NULL)
> > +		/*
> > +		 * ima_dump_measurement_list() does not modify the list,
> > +		 * cut_pos remains the same even if it was computed before
> > +		 * the lock.
> > +		 */
> > +		__list_cut_position(&ima_measurements_trim,
> > +				    &ima_measurements_staged, cut_pos);
> > +
> > +	atomic_long_sub(num_to_remove, &ima_num_entries[BINARY_STAGED]);
> > +	atomic_long_add(atomic_long_read(&ima_num_entries[BINARY_STAGED]),
> > +			&ima_num_entries[BINARY]);
> > +	atomic_long_set(&ima_num_entries[BINARY_STAGED], 0);
> > +
> > +	if (IS_ENABLED(CONFIG_IMA_KEXEC)) {
> > +		binary_runtime_size[BINARY_STAGED] -= size_to_remove;
> > +		binary_runtime_size[BINARY] +=
> > +					binary_runtime_size[BINARY_STAGED];
> > +		binary_runtime_size[BINARY_STAGED] = 0;
> > +	}
> > +
> > +	/*
> > +	 * Splice (prepend) any remaining non-deleted staged entries to the
> > +	 * active list (RCU not needed, there cannot be concurrent readers).
> > +	 */
> > +	list_splice(&ima_measurements_staged, &ima_measurements);
> > +	INIT_LIST_HEAD(&ima_measurements_staged);
> > +	mutex_unlock(&ima_extend_list_mutex);
> > +
> > +	ima_queue_delete(&ima_measurements_trim, false);
> > +	return ret;
> > +}
> > +
> >   static void ima_queue_delete(struct list_head *head, bool flush_htable)
> >   {
> >   	struct ima_queue_entry *qe, *qe_tmp;
>