Re: [PATCH V2 1/1] IMA event log trimming

[steven chen <chenste@linux.microsoft.com>]

On 12/10/2025 3:53 PM, steven chen wrote:
> This patch is for trimming N entries of the IMA event logs. It will also
> cleaning the hash table if ima_flush_htable is set.
>
> It provides a userspace interface ima_trim_log that can be used to input
> number N to let kernel to trim N entries of IMA event logs. When read
> this interface, it returns number of entries trimmed last time.
>
> Signed-off-by: steven chen <chenste@linux.microsoft.com>
> ---
>   .../admin-guide/kernel-parameters.txt         |   4 +
>   security/integrity/ima/ima.h                  |   2 +
>   security/integrity/ima/ima_fs.c               | 175 +++++++++++++++++-
>   security/integrity/ima/ima_queue.c            |  64 +++++++
>   4 files changed, 241 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index e92c0056e4e0..cd1a1d0bf0e2 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2197,6 +2197,10 @@
>   			Use the canonical format for the binary runtime
>   			measurements, instead of host native format.
>   
> +	ima_flush_htable  [IMA]
> +			Flush the measurement list hash table when trim all
> +			or a part of it for deletion.
> +
>   	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 e3d71d8d56e3..ab0e30ee25ea 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -246,8 +246,10 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
>   
>   #ifdef CONFIG_IMA_KEXEC
>   void ima_measure_kexec_event(const char *event_name);
> +long ima_purge_event_log(long number_logs);
>   #else
>   static inline void ima_measure_kexec_event(const char *event_name) {}
> +static inline long ima_purge_event_log(long number_logs) { return 0; }
>   #endif
>   
>   /*
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index 87045b09f120..410f7d03c43f 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -21,6 +21,9 @@
>   #include <linux/rcupdate.h>
>   #include <linux/parser.h>
>   #include <linux/vmalloc.h>
> +#include <linux/ktime.h>
> +#include <linux/timekeeping.h>
> +#include <linux/ima.h>
>   
>   #include "ima.h"
>   
> @@ -38,6 +41,14 @@ __setup("ima_canonical_fmt", default_canonical_fmt_setup);
>   
>   static int valid_policy = 1;
>   
> +#define IMA_LOG_TRIM_REQ_LENGTH 11
> +#define IMA_LOG_TRIM_EVENT_LEN 256
> +
> +static long trimcount;
> +/* mutex protects atomicity of trimming measurement list requests */
> +static DEFINE_MUTEX(ima_measure_lock);
> +static long ima_measure_users;
> +
>   static ssize_t ima_show_htable_value(char __user *buf, size_t count,
>   				     loff_t *ppos, atomic_long_t *val)
>   {
> @@ -202,16 +213,65 @@ static const struct seq_operations ima_measurments_seqops = {
>   	.show = ima_measurements_show
>   };
>   
> +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;
> +
> +	mutex_lock(&ima_measure_lock);
> +	if ((write && ima_measure_users != 0) ||
> +	    (!write && ima_measure_users < 0)) {
> +		mutex_unlock(&ima_measure_lock);
> +		return -EBUSY;
> +	}
> +
> +	ret = seq_open(file, seq_ops);
> +	if (ret < 0) {
> +		mutex_unlock(&ima_measure_lock);
> +		return ret;
> +	}
> +
> +	if (write)
> +		ima_measure_users--;
> +	else
> +		ima_measure_users++;
> +
> +	mutex_unlock(&ima_measure_lock);
> +	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;
> +
> +	mutex_lock(&ima_measure_lock);
> +	ret = seq_release(inode, file);
> +	if (!ret) {
> +		if (write)
> +			ima_measure_users++;
> +		else
> +			ima_measure_users--;
> +	}
> +
> +	mutex_unlock(&ima_measure_lock);
> +	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)
> @@ -279,14 +339,111 @@ 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 void ima_measure_trim_event(const long number_logs)
> +{
> +	char ima_log_trim_event[IMA_LOG_TRIM_EVENT_LEN];
> +	struct timespec64 ts;
> +	u64 time_ns;
> +	int n;
> +
> +	ktime_get_real_ts64(&ts);
> +	time_ns = (u64)ts.tv_sec * 1000000000ULL + ts.tv_nsec;
> +	n = scnprintf(ima_log_trim_event, IMA_LOG_TRIM_EVENT_LEN,
> +		      "time=%llu; log trim this time=%lu;",
> +		       time_ns, number_logs);
> +
> +	ima_measure_critical_data("ima_log_trim", "trim ima event logs", ima_log_trim_event, n, false, NULL, 0);
> +}
> +
> +static int ima_log_trim_open(struct inode *inode, struct file *file)
> +{
> +	bool write = !!(file->f_mode & FMODE_WRITE);
> +
> +	if (!write && capable(CAP_SYS_ADMIN))
> +		return 0;
> +	else if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +
> +	return _ima_measurements_open(inode, file, &ima_measurments_seqops);
> +}
> +
> +static ssize_t ima_log_trim_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
> +{
> +	char tmpbuf[IMA_LOG_TRIM_REQ_LENGTH];	/* greater than largest 'long' string value */
> +	ssize_t len;
> +
> +	len = scnprintf(tmpbuf, sizeof(tmpbuf), "%li\n", trimcount);
> +	return simple_read_from_buffer(buf, size, ppos, tmpbuf, len);
> +}
> +
> +static ssize_t ima_log_trim_write(struct file *file,
> +				  const char __user *buf, size_t datalen, loff_t *ppos)
> +{
> +	unsigned char req[IMA_LOG_TRIM_REQ_LENGTH];
> +	long count, n;
> +	int ret;
> +
> +	if (*ppos > 0 || datalen > IMA_LOG_TRIM_REQ_LENGTH || datalen < 2) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	n = (int)datalen;
> +
> +	ret = copy_from_user(req, buf, datalen);
> +	if (ret < 0)
> +		goto out;
> +
> +	count = 0;
> +	for (int i = 0; i < n; ++i) {
> +		if (req[i] < '0' || req[i] > '9') {
> +			ret = -EINVAL;
> +			goto out;
> +		}
> +		count = count * 10 + req[i] - '0';
> +	}
> +	ret = ima_purge_event_log(count);
> +
> +	if (ret < 0)
> +		goto out;
> +
> +	trimcount = ret;
> +
> +	if (trimcount > 0)
> +		ima_measure_trim_event(trimcount);
> +
> +	ret = datalen;
> +out:
> +	return ret;
> +}
> +
> +static int ima_log_trim_release(struct inode *inode, struct file *file)
> +{
> +	bool write = !!(file->f_mode & FMODE_WRITE);
> +	if (!write && capable(CAP_SYS_ADMIN))
> +		return 0;
> +	else if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +
> +	return ima_measurements_release(inode, file);
> +}
> +
> +static const struct file_operations ima_log_trim_ops = {
> +	.open = ima_log_trim_open,
> +	.read = ima_log_trim_read,
> +	.write = ima_log_trim_write,
> +	.llseek = generic_file_llseek,
> +	.release = ima_log_trim_release
>   };
>   
>   static ssize_t ima_read_policy(char *path)
> @@ -528,6 +685,16 @@ int __init ima_fs_init(void)
>   		goto out;
>   	}
>   
> +	dentry = securityfs_create_file("ima_trim_log",
> +					S_IRUSR | S_IRGRP | S_IWUSR | S_IWGRP,
> +					ima_dir, NULL, &ima_log_trim_ops);
> +	if (IS_ERR(dentry)) {
> +		ret = PTR_ERR(dentry);
> +		goto out;
> +	}
> +
> +	trimcount = 0;
> +
>   	dentry = securityfs_create_file("runtime_measurements_count",
>   				   S_IRUSR | S_IRGRP, ima_dir, NULL,
>   				   &ima_measurements_count_ops);
> diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
> index 590637e81ad1..77ab52469727 100644
> --- a/security/integrity/ima/ima_queue.c
> +++ b/security/integrity/ima/ima_queue.c
> @@ -22,6 +22,14 @@
>   
>   #define AUDIT_CAUSE_LEN_MAX 32
>   
> +bool ima_flush_htable;
> +static int __init ima_flush_htable_setup(char *str)
> +{
> +	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;
>   
> @@ -220,6 +228,62 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
>   	return result;
>   }
>   
> +/* Delete the IMA event logs */
> +long ima_purge_event_log(long number_logs)
> +{
> +	struct ima_queue_entry *qe, *qe_tmp;
> +	LIST_HEAD(ima_measurements_staged);
> +	unsigned int i;
> +	long cur = number_logs;
> +
> +	if (number_logs <= 0)
> +		return number_logs;
> +
> +	mutex_lock(&ima_extend_list_mutex);
> +
> +
> +	list_for_each_entry(qe, &ima_measurements, later) {
> +		if (--number_logs == 0)
> +			break;
> +	}
> +
> +	if (number_logs > 0) {
> +		mutex_unlock(&ima_extend_list_mutex);
> +		return -ENOENT;
> +	}
> +
> +	__list_cut_position(&ima_measurements_staged, &ima_measurements,
> +				    &qe->later);
> +	atomic_long_sub(cur, &ima_htable.len);
> +
> +	if (!IS_ENABLED(CONFIG_IMA_DISABLE_HTABLE) && ima_flush_htable) {
> +		list_for_each_entry(qe, &ima_measurements_staged, later)
> +			/* It can race with ima_lookup_digest_entry(). */
> +			hlist_del_rcu(&qe->hnext);
> +	}

If the h table can be staged during the locking period and deleted after 
unlocking, the time
the list is held will be reduced.

I will work on this, and any suggestions are greatly appreciated.

Thanks,

Steven

> +
> +	mutex_unlock(&ima_extend_list_mutex);
> +
> +
> +	list_for_each_entry_safe(qe, qe_tmp, &ima_measurements_staged, later) {
> +		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);
> +
> +		if (ima_flush_htable) {
> +			kfree(qe->entry->digests);
> +			kfree(qe->entry);
> +			kfree(qe);
> +		}
> +	}
> +
> +	return cur;
> +}
> +
>   int ima_restore_measurement_entry(struct ima_template_entry *entry)
>   {
>   	int result = 0;