[PATCH v4 09/13] ima: Add support for staging measurements with prompt
Roberto Sassu
roberto.sassu at huaweicloud.com
Fri Mar 27 16:45:36 UTC 2026
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 at 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 at linux.microsoft.com> (staging revert)
> > Signed-off-by: Roberto Sassu <roberto.sassu at 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;
>
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