Re: [PATCH v20 03/20] ipe: add evaluation loop

["Serge E. Hallyn" <serge@hallyn.com>]

On Fri, Aug 02, 2024 at 11:08:17PM -0700, Fan Wu wrote:
> From: Deven Bowers <deven.desai@linux.microsoft.com>
> 
> Introduce a core evaluation function in IPE that will be triggered by
> various security hooks (e.g., mmap, bprm_check, kexec). This function
> systematically assesses actions against the defined IPE policy, by
> iterating over rules specific to the action being taken. This critical
> addition enables IPE to enforce its security policies effectively,
> ensuring that actions intercepted by these hooks are scrutinized for policy
> compliance before they are allowed to proceed.
> 
> Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>
> Signed-off-by: Fan Wu <wufan@linux.microsoft.com>

(started at this longer than I care to admit)

Reviewed-by: Serge Hallyn <serge@hallyn.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
> 
> v12:
> + Correct an rcu_read_unlock usage
> + Add a WARN to unknown op during evaluation
> 
> v13:
> + No changes
> 
> v14:
> + No changes
> 
> v15:
> + No changes
> 
> v16:
> + No changes
> 
> v17:
> + Add years to license header
> + Fix code and documentation style issues
> 
> v18:
> + No changes
> 
> v19:
> + No changes
> 
> v20:
> + No changes
> ---
>  security/ipe/Makefile |   1 +
>  security/ipe/eval.c   | 102 ++++++++++++++++++++++++++++++++++++++++++
>  security/ipe/eval.h   |  24 ++++++++++
>  3 files changed, 127 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 3093de1afd3e..4cc17eb92060 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..f6a681ca49f6
> --- /dev/null
> +++ b/security/ipe/eval.c
> @@ -0,0 +1,102 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2020-2024 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 rule property.
> + * @ctx: Supplies a pointer to the context to be evaluated.
> + * @p: Supplies a pointer to the property to be evaluated.
> + *
> + * This is a placeholder. The actual function will be introduced in the
> + * latter commits.
> + *
> + * 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 evaluations happen against the IPE policy.
> + *
> + * Return:
> + * * %0		- Success
> + * * %-EACCES	- @ctx did not pass evaluation
> + */
> +int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)
> +{
> +	const struct ipe_op_table *rules = NULL;
> +	const struct ipe_rule *rule = NULL;
> +	struct ipe_policy *pol = NULL;
> +	struct ipe_prop *prop = NULL;
> +	enum ipe_action_type action;
> +	bool match = false;
> +
> +	rcu_read_lock();
> +
> +	pol = rcu_dereference(ipe_active_policy);
> +	if (!pol) {
> +		rcu_read_unlock();
> +		return 0;
> +	}
> +
> +	if (ctx->op == IPE_OP_INVALID) {
> +		if (pol->parsed->global_default_action == IPE_ACTION_DENY) {
> +			rcu_read_unlock();
> +			return -EACCES;
> +		}
> +		if (pol->parsed->global_default_action == IPE_ACTION_INVALID)
> +			WARN(1, "no default rule set for unknown op, ALLOW it");
> +		rcu_read_unlock();
> +		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 = 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..b137f2107852
> --- /dev/null
> +++ b/security/ipe/eval.h
> @@ -0,0 +1,24 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2020-2024 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 */
> -- 
> 2.44.0