[RFC PATCH v11 03/19] ipe: add evaluation loop

Fan Wu
2023-10-04T22:09:55Z

From: Deven Bowers <deven.desai@linux.microsoft.com>

IPE must have a centralized function to evaluate incoming callers
against IPE's policy. This iteration of the policy for against the rules
for that specific caller is known as the evaluation loop.

Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>
Signed-off-by: Fan Wu <wufan@linux.microsoft.com>

---
v2:
+ Split evaluation loop, access control hooks, and evaluation loop from policy parser and userspace interface to pass mailing list character limit

v3:
+ Move ipe_load_properties to patch 04.
+ Remove useless 0-initializations Prefix extern variables with ipe_
+ Remove kernel module parameters, as these are exposed through sysctls.
+ Add more prose to the IPE base config option help text.
+ Use GFP_KERNEL for audit_log_start.
+ Remove unnecessary caching system.
+ Remove comments from headers
+ Use rcu_access_pointer for rcu-pointer null check
+ Remove usage of reqprot; use prot only.
+Move policy load and activation audit event to 03/12

v4:
+ Remove sysctls in favor of securityfs nodes
+ Re-add kernel module parameters, as these are now exposed through securityfs.
+ Refactor property audit loop to a separate function.

v5:
+ fix minor grammatical errors
+ do not group rule by curly-brace in audit record,
+ reconstruct the exact rule.

v6:
+ No changes

v7:
+ Further split lsm creation into a separate commit from the evaluation loop and audit system, for easier review.
+ Propagating changes to support the new ipe_context structure in the evaluation loop.

v8:
+ Remove ipe_hook enumeration; hooks can be correlated via syscall record.

v9:
+ Remove ipe_context related code and simplify the evaluation loop.

v10:
+ Split eval part and boot_verified part

v11:
+ Fix code style issues
---
security/ipe/Makefile | 1 +
security/ipe/eval.c | 96 +++++++++++++++++++++++++++++++++++++++++++
security/ipe/eval.h | 24 +++++++++++
3 files changed, 121 insertions(+)
create mode 100644 security/ipe/eval.c
create mode 100644 security/ipe/eval.h

diff --git a/security/ipe/Makefile b/security/ipe/Makefile
index c09aec4904f2..57fe922cf1fc 100644
--- a/security/ipe/Makefile
+++ b/security/ipe/Makefile
@@ -6,6 +6,7 @@
#

obj-$(CONFIG_SECURITY_IPE) += \
+ eval.o \
ipe.o \
policy.o \
policy_parser.o \
diff --git a/security/ipe/eval.c b/security/ipe/eval.c
new file mode 100644
index 000000000000..5533c359bbeb
--- /dev/null
+++ b/security/ipe/eval.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include <linux/fs.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/file.h>
+#include <linux/sched.h>
+#include <linux/rcupdate.h>
+
+#include "ipe.h"
+#include "eval.h"
+#include "policy.h"
+
+struct ipe_policy __rcu *ipe_active_policy;
+
+/**
+ * evaluate_property - Analyze @ctx against a property.
+ * @ctx: Supplies a pointer to the context to be evaluated.
+ * @p: Supplies a pointer to the property to be evaluated.
+ *
+ * Return:
+ * * true - The current @ctx match the @p
+ * * false - The current @ctx doesn't match the @p
+ */
+static bool evaluate_property(const struct ipe_eval_ctx *const ctx,
+ struct ipe_prop *p)
+{
+ return false;
+}
+
+/**
+ * ipe_evaluate_event - Analyze @ctx against the current active policy.
+ * @ctx: Supplies a pointer to the context to be evaluated.
+ *
+ * This is the loop where all policy evaluation happens against IPE policy.
+ *
+ * Return:
+ * * 0 - OK
+ * * -EACCES - @ctx did not pass evaluation.
+ * * !0 - Error
+ */
+int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)
+{
+ bool match = false;
+ enum ipe_action_type action;
+ struct ipe_policy *pol = NULL;
+ const struct ipe_rule *rule = NULL;
+ const struct ipe_op_table *rules = NULL;
+ struct ipe_prop *prop = NULL;
+
+ rcu_read_lock();
+
+ pol = rcu_dereference(ipe_active_policy);
+ if (!pol) {
+ rcu_read_unlock();
+ return 0;
+ }
+
+ if (ctx->op == IPE_OP_INVALID) {
+ rcu_read_unlock();
+ if (pol->parsed->global_default_action == IPE_ACTION_DENY)
+ return -EACCES;
+ return 0;
+ }
+
+ rules = &pol->parsed->rules[ctx->op];
+
+ list_for_each_entry(rule, &rules->rules, next) {
+ match = true;
+
+ list_for_each_entry(prop, &rule->props, next) {
+ match = match && evaluate_property(ctx, prop);
+ if (!match)
+ break;
+ }
+
+ if (match)
+ break;
+ }
+
+ if (match)
+ action = rule->action;
+ else if (rules->default_action != IPE_ACTION_INVALID)
+ action = rules->default_action;
+ else
+ action = pol->parsed->global_default_action;
+
+ rcu_read_unlock();
+ if (action == IPE_ACTION_DENY)
+ return -EACCES;
+
+ return 0;
+}
diff --git a/security/ipe/eval.h b/security/ipe/eval.h
new file mode 100644
index 000000000000..6b434515968f
--- /dev/null
+++ b/security/ipe/eval.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#ifndef _IPE_EVAL_H
+#define _IPE_EVAL_H
+
+#include <linux/file.h>
+#include <linux/types.h>
+
+#include "policy.h"
+
+extern struct ipe_policy __rcu *ipe_active_policy;
+
+struct ipe_eval_ctx {
+ enum ipe_op_type op;
+
+ const struct file *file;
+};
+
+int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx);
+
+#endif /* _IPE_EVAL_H */
--
2.25.1