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Subject[PATCH v2 1/5 RFC] added ima hook for buffer, being enabled as a policy
Date
From: Prakhar Srivastava <prsriva02@gmail.com>

Signed-off-by: Prakhar Srivastava <prsriva@microsoft.com>
---
Currently for soft reboot(kexec_file_load) the kernel file and
signature is measured by IMA. The cmdline args used to load the kernel
is not measured.
The boot aggregate that gets calculated will have no change since the
EFI loader has not been triggered.
Adding the kexec cmdline args measure and kernel version will add some
attestable criteria.

This adds a new ima hook ima_buffer_check and a policy entry BUFFER_CHECK.
This enables buffer has measurements into ima log

Documentation/ABI/testing/ima_policy | 1 +
include/linux/ima.h | 13 +++-
security/integrity/ima/ima.h | 1 +
security/integrity/ima/ima_main.c | 95 ++++++++++++++++++++++++++++
security/integrity/ima/ima_policy.c | 14 +++-
5 files changed, 122 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index bb0f9a135e21..676088c7ab26 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -28,6 +28,7 @@ Description:
base: func:= [BPRM_CHECK][MMAP_CHECK][FILE_CHECK][MODULE_CHECK]
[FIRMWARE_CHECK]
[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
+ [BUFFER_CHECK]
mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
[[^]MAY_EXEC]
fsmagic:= hex value
diff --git a/include/linux/ima.h b/include/linux/ima.h
index 7f6952f8d6aa..733d0cb9dedc 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -14,6 +14,12 @@
#include <linux/kexec.h>
struct linux_binprm;

+enum __buffer_id {
+ KERNEL_VERSION,
+ KEXEC_CMDLINE,
+ MAX_BUFFER_ID = KEXEC_CMDLINE
+} buffer_id;
+
#ifdef CONFIG_IMA
extern int ima_bprm_check(struct linux_binprm *bprm);
extern int ima_file_check(struct file *file, int mask, int opened);
@@ -23,7 +29,7 @@ extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
enum kernel_read_file_id id);
extern void ima_post_path_mknod(struct dentry *dentry);
-
+extern void ima_buffer_check(const void *buff, int size, enum buffer_id id);
#ifdef CONFIG_IMA_KEXEC
extern void ima_add_kexec_buffer(struct kimage *image);
#endif
@@ -65,6 +71,11 @@ static inline void ima_post_path_mknod(struct dentry *dentry)
return;
}

+static inline void ima_buffer_check(const void *buff, int size,
+ enum buffer_id id)
+{
+ return;
+}
#endif /* CONFIG_IMA */

#ifndef CONFIG_IMA_KEXEC
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index b563fbd4d122..b71f2f6f7421 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -181,6 +181,7 @@ enum ima_hooks {
FIRMWARE_CHECK,
KEXEC_KERNEL_CHECK,
KEXEC_INITRAMFS_CHECK,
+ BUFFER_CHECK,
POLICY_CHECK,
MAX_CHECK
};
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 2aebb7984437..6408cadaadbb 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -155,6 +155,84 @@ void ima_file_free(struct file *file)
ima_check_last_writer(iint, inode, file);
}

+/*
+ * process_buffer_measurement - Measure the buffer passed to ima log.
+ * (Instead of using the file hash the buffer hash is used).
+ * @buff - The buffer that needs to be added to the log
+ * @size - size of buffer(in bytes)
+ * @id - buffer id, this is differentiator for the various buffers
+ * that can be measured.
+ *
+ * The buffer passed is added to the ima logs.
+ * If the sig template is used, then the sig field contains the buffer.
+ *
+ * On success return 0.
+ * On error cases surface errors from ima calls.
+ */
+static int process_buffer_measurement(const void *buff, int size,
+ enum buffer_id id)
+{
+ int ret = -EINVAL;
+ struct ima_template_entry *entry = NULL;
+ struct integrity_iint_cache tmp_iint, *iint = &tmp_iint;
+ struct ima_event_data event_data = {iint, NULL, NULL,
+ NULL, 0, NULL};
+ struct {
+ struct ima_digest_data hdr;
+ char digest[IMA_MAX_DIGEST_SIZE];
+ } hash;
+ char *name = NULL;
+ int violation = 0;
+ int pcr = CONFIG_IMA_MEASURE_PCR_IDX;
+
+ if (!buff || size == 0)
+ goto err_out;
+
+ if (ima_get_action(NULL, 0, BUFFER_CHECK, &pcr) != IMA_MEASURE)
+ goto err_out;
+
+ switch (buffer_id) {
+ case KERNEL_VERSION:
+ name = "Kernel-version";
+ break;
+ case KEXEC_CMDLINE:
+ name = "Kexec-cmdline";
+ break;
+ default:
+ goto err_out;
+ }
+
+ memset(iint, 0, sizeof(*iint));
+ memset(&hash, 0, sizeof(hash));
+
+ event_data.filename = name;
+
+ iint->ima_hash = &hash.hdr;
+ iint->ima_hash->algo = ima_hash_algo;
+ iint->ima_hash->length = hash_digest_size[ima_hash_algo];
+
+ ret = ima_calc_buffer_hash(buff, size, iint->ima_hash);
+ if (ret < 0)
+ goto err_out;
+
+ ret = ima_alloc_init_template(&event_data, &entry);
+ if (ret < 0)
+ goto err_out;
+
+ ret = ima_store_template(entry, violation, NULL,
+ buff, pcr);
+ if (ret < 0) {
+ ima_free_template_entry(entry);
+ goto err_out;
+ }
+
+ return 0;
+
+err_out:
+ pr_err("Error in adding buffer measure: %d\n", ret);
+ return ret;
+}
+
static int process_measurement(struct file *file, char *buf, loff_t size,
int mask, enum ima_hooks func, int opened)
{
@@ -370,6 +448,23 @@ int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
return 0;
}

+/**
+ * ima_buffer_check - based on policy, collect & store buffer measurement
+ * @buf: pointer to buffer
+ * @size: size of buffer
+ * @buffer_id: caller identifier
+ *
+ * Buffers can only be measured, not appraised. The buffer identifier
+ * is used as the measurement list entry name (eg. boot_cmdline).
+ */
+void ima_buffer_check(const void *buf, int size, enum buffer_id id)
+{
+ if (buf && size != 0)
+ process_buffer_measurement(buf, size, id);
+
+ return;
+}
+
static int read_idmap[READING_MAX_ID] = {
[READING_FIRMWARE] = FIRMWARE_CHECK,
[READING_MODULE] = MODULE_CHECK,
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 3ab1067db624..cefe1a188f31 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -231,6 +231,12 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
const struct cred *cred = current_cred();
int i;

+ // Incase of BUFFER_CHECK, Inode is NULL
+ if (!inode) {
+ if ((rule->flags & IMA_FUNC) && (rule->func == func))
+ return true;
+ return false;
+ }
if ((rule->flags & IMA_FUNC) &&
(rule->func != func && func != POST_SETATTR))
return false;
@@ -665,6 +671,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
else if (strcmp(args[0].from, "KEXEC_INITRAMFS_CHECK")
== 0)
entry->func = KEXEC_INITRAMFS_CHECK;
+ else if (strcmp(args[0].from, "BUFFER_CHECK") == 0)
+ entry->func = BUFFER_CHECK;
else if (strcmp(args[0].from, "POLICY_CHECK") == 0)
entry->func = POLICY_CHECK;
else
@@ -944,7 +952,7 @@ enum {
func_file = 0, func_mmap, func_bprm,
func_module, func_firmware, func_post,
func_kexec_kernel, func_kexec_initramfs,
- func_policy
+ func_buffer, func_policy
};

static char *func_tokens[] = {
@@ -956,6 +964,7 @@ static char *func_tokens[] = {
"POST_SETATTR",
"KEXEC_KERNEL_CHECK",
"KEXEC_INITRAMFS_CHECK",
+ "BUFFER_CHECK",
"POLICY_CHECK"
};

@@ -1027,6 +1036,9 @@ static void policy_func_show(struct seq_file *m, enum ima_hooks func)
case KEXEC_INITRAMFS_CHECK:
seq_printf(m, pt(Opt_func), ft(func_kexec_initramfs));
break;
+ case BUFFER_CHECK:
+ seq_printf(m, pt(Opt_func), ft(func_buffer));
+ break;
case POLICY_CHECK:
seq_printf(m, pt(Opt_func), ft(func_policy));
break;
--
2.17.1
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