[RFC PATCH v9 02/16] ipe: add policy parser

[Fan Wu]

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

IPE's interpretation of the what the user trusts is accomplished through
its policy. IPE's design is to not provide support for a single trust
provider, but to support multiple providers to enable the end-user to
choose the best one to seek their needs.

This requires the policy to be rather flexible and modular so that
integrity providers, like fs-verity, dm-verity, dm-integrity, or
some other system, can plug into the policy with minimal code changes.

Signed-off-by: Deven Bowers <deven.desai at linux.microsoft.com>
Signed-off-by: Fan Wu <wufan at 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 policy load and activation audit event to 03/12
  + Fix a potential panic when a policy failed to load.
  + use pr_warn for a failure to parse instead of an
    audit record
  + Remove comments from headers
  + Add lockdep assertions to ipe_update_active_policy and
    ipe_activate_policy
  + Fix up warnings with checkpatch --strict
  + Use file_ns_capable for CAP_MAC_ADMIN for securityfs
    nodes.
  + Use memdup_user instead of kzalloc+simple_write_to_buffer.
  + Remove strict_parse command line parameter, as it is added
    by the sysctl command line.
  + Prefix extern variables with ipe_

v4:
  + Remove securityfs to reverse-dependency
  + Add SHA1 reverse dependency.
  + Add versioning scheme for IPE properties, and associated
    interface to query the versioning scheme.
  + Cause a parser to always return an error on unknown syntax.
  + Remove strict_parse option
  + Change active_policy interface from sysctl, to securityfs,
    and change scheme.

v5:
  + Cause an error if a default action is not defined for each
    operaiton.
  + Minor function renames

v6:
  + No changes

v7:
  + Further split parser and userspace interface into two
    separate commits, for easier review.

  + Refactor policy parser to make code cleaner via introducing a
    more modular design, for easier extension of policy, and
    easier review.

v8:
  + remove unnecessary pr_info emission on parser loading

  + add explicit newline to the pr_err emitted when a parser
    fails to load.

v9:
  + switch to match table to parse policy

  + remove quote syntax and KERNEL_READ operation
---
 security/ipe/Makefile        |   2 +
 security/ipe/policy.c        |  99 +++++++
 security/ipe/policy.h        |  77 ++++++
 security/ipe/policy_parser.c | 515 +++++++++++++++++++++++++++++++++++
 security/ipe/policy_parser.h |  11 +
 5 files changed, 704 insertions(+)
 create mode 100644 security/ipe/policy.c
 create mode 100644 security/ipe/policy.h
 create mode 100644 security/ipe/policy_parser.c
 create mode 100644 security/ipe/policy_parser.h

diff --git a/security/ipe/Makefile b/security/ipe/Makefile
index 571648579991..16bbe80991f1 100644
--- a/security/ipe/Makefile
+++ b/security/ipe/Makefile
@@ -8,3 +8,5 @@
 obj-$(CONFIG_SECURITY_IPE) += \
 	hooks.o \
 	ipe.o \
+	policy.o \
+	policy_parser.o \
diff --git a/security/ipe/policy.c b/security/ipe/policy.c
new file mode 100644
index 000000000000..e446f4b84152
--- /dev/null
+++ b/security/ipe/policy.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include "ipe.h"
+#include "policy.h"
+#include "policy_parser.h"
+#include "digest.h"
+
+#include <linux/verification.h>
+
+/**
+ * ipe_free_policy - Deallocate a given IPE policy.
+ * @p: Supplies the policy to free.
+ *
+ * Safe to call on IS_ERR/NULL.
+ */
+void ipe_free_policy(struct ipe_policy *p)
+{
+	if (IS_ERR_OR_NULL(p))
+		return;
+
+	free_parsed_policy(p->parsed);
+	if (!p->pkcs7)
+		kfree(p->text);
+	kfree(p->pkcs7);
+	kfree(p);
+}
+
+static int set_pkcs7_data(void *ctx, const void *data, size_t len,
+			  size_t asn1hdrlen)
+{
+	struct ipe_policy *p = ctx;
+
+	p->text = (const char *)data;
+	p->textlen = len;
+
+	return 0;
+}
+
+/**
+ * ipe_new_policy - Allocate and parse an ipe_policy structure.
+ *
+ * @text: Supplies a pointer to the plain-text policy to parse.
+ * @textlen: Supplies the length of @text.
+ * @pkcs7: Supplies a pointer to a pkcs7-signed IPE policy.
+ * @pkcs7len: Supplies the length of @pkcs7.
+ *
+ * @text/@textlen Should be NULL/0 if @pkcs7/@pkcs7len is set.
+ *
+ * The result will still need to be associated with a context via
+ * ipe_add_policy.
+ *
+ * Return:
+ * * !IS_ERR	- Success
+ * * -EBADMSG	- Policy is invalid
+ * * -ENOMEM	- Out of memory
+ */
+struct ipe_policy *ipe_new_policy(const char *text, size_t textlen,
+				  const char *pkcs7, size_t pkcs7len)
+{
+	int rc = 0;
+	struct ipe_policy *new = NULL;
+
+	new = kzalloc(sizeof(*new), GFP_KERNEL);
+	if (!new)
+		return ERR_PTR(-ENOMEM);
+
+	if (!text) {
+		new->pkcs7len = pkcs7len;
+		new->pkcs7 = kmemdup(pkcs7, pkcs7len, GFP_KERNEL);
+		if (!new->pkcs7) {
+			rc = -ENOMEM;
+			goto err;
+		}
+
+		rc = verify_pkcs7_signature(NULL, 0, new->pkcs7, pkcs7len, NULL,
+					    VERIFYING_UNSPECIFIED_SIGNATURE,
+					    set_pkcs7_data, new);
+		if (rc)
+			goto err;
+	} else {
+		new->textlen = textlen;
+		new->text = kstrdup(text, GFP_KERNEL);
+		if (!new->text) {
+			rc = -ENOMEM;
+			goto err;
+		}
+	}
+
+	rc = parse_policy(new);
+	if (rc)
+		goto err;
+
+	return new;
+err:
+	return ERR_PTR(rc);
+}
diff --git a/security/ipe/policy.h b/security/ipe/policy.h
new file mode 100644
index 000000000000..6af2d9a811ec
--- /dev/null
+++ b/security/ipe/policy.h
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+#ifndef IPE_POLICY_H
+#define IPE_POLICY_H
+
+#include <linux/list.h>
+#include <linux/types.h>
+
+enum ipe_op_type {
+	ipe_op_exec = 0,
+	ipe_op_firmware,
+	ipe_op_kernel_module,
+	ipe_op_kexec_image,
+	ipe_op_kexec_initramfs,
+	ipe_op_ima_policy,
+	ipe_op_ima_x509,
+	ipe_op_max
+};
+
+enum ipe_action_type {
+	ipe_action_allow = 0,
+	ipe_action_deny,
+	ipe_action_max
+};
+
+enum ipe_prop_type {
+	ipe_prop_max
+};
+
+struct ipe_prop {
+	struct list_head next;
+	enum ipe_prop_type type;
+	void *value;
+};
+
+struct ipe_rule {
+	enum ipe_op_type op;
+	enum ipe_action_type action;
+	struct list_head props;
+	struct list_head next;
+};
+
+struct ipe_op_table {
+	struct list_head rules;
+	enum ipe_action_type default_action;
+};
+
+struct ipe_parsed_policy {
+	const char *name;
+	struct {
+		u16 major;
+		u16 minor;
+		u16 rev;
+	} version;
+
+	enum ipe_action_type global_default_action;
+
+	struct ipe_op_table rules[ipe_op_max];
+};
+
+struct ipe_policy {
+	const char     *pkcs7;
+	size_t		pkcs7len;
+
+	const char     *text;
+	size_t		textlen;
+
+	struct ipe_parsed_policy *parsed;
+};
+
+struct ipe_policy *ipe_new_policy(const char *text, size_t textlen,
+				  const char *pkcs7, size_t pkcs7len);
+void ipe_free_policy(struct ipe_policy *pol);
+
+#endif /* IPE_POLICY_H */
diff --git a/security/ipe/policy_parser.c b/security/ipe/policy_parser.c
new file mode 100644
index 000000000000..c7ba0e865366
--- /dev/null
+++ b/security/ipe/policy_parser.c
@@ -0,0 +1,515 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include "policy.h"
+#include "policy_parser.h"
+#include "digest.h"
+
+#include <linux/parser.h>
+
+#define START_COMMENT	'#'
+
+/**
+ * new_parsed_policy - Allocate and initialize a parsed policy.
+ *
+ * Return:
+ * * !IS_ERR	- OK
+ * * -ENOMEM	- Out of memory
+ */
+static struct ipe_parsed_policy *new_parsed_policy(void)
+{
+	size_t i = 0;
+	struct ipe_parsed_policy *p = NULL;
+	struct ipe_op_table *t = NULL;
+
+	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (!p)
+		return ERR_PTR(-ENOMEM);
+
+	p->global_default_action = ipe_action_max;
+
+	for (i = 0; i < ARRAY_SIZE(p->rules); ++i) {
+		t = &p->rules[i];
+
+		t->default_action = ipe_action_max;
+		INIT_LIST_HEAD(&t->rules);
+	}
+
+	return p;
+}
+
+/**
+ * remove_comment - Truncate all chars following START_COMMENT in a string.
+ *
+ * @line: Supplies a poilcy line string for preprocessing.
+ */
+static void remove_comment(char *line)
+{
+	size_t i, len = 0;
+
+	len = strlen(line);
+	for (i = 0; i < len && line[i] != START_COMMENT; ++i)
+		;
+
+	line[i] = '\0';
+}
+
+/**
+ * remove_trailing_spaces - Truncate all trailing spaces in a string.
+ *
+ * @line: Supplies a poilcy line string for preprocessing.
+ */
+static void remove_trailing_spaces(char *line)
+{
+	size_t i, len = 0;
+
+	len = strlen(line);
+	for (i = len; i > 0 && (line[i - 1] == ' ' || line[i - 1] == '\t'); --i)
+		;
+
+	line[i] = '\0';
+}
+
+/**
+ * parse_version - Parse policy version.
+ * @ver: Supplies a version string to be parsed.
+ * @p: Supplies the partial parsed policy.
+ *
+ * Return:
+ * * 0	- OK
+ * * !0	- Standard errno
+ */
+static int parse_version(char *ver, struct ipe_parsed_policy *p)
+{
+	int rc = 0;
+	size_t sep_count = 0;
+	char *token;
+	u16 *const cv[] = { &p->version.major, &p->version.minor, &p->version.rev };
+
+	while ((token = strsep(&ver, ".")) != NULL) {
+		/* prevent overflow */
+		if (sep_count >= ARRAY_SIZE(cv)) {
+			rc = -EBADMSG;
+			goto err;
+		}
+
+		rc = kstrtou16(token, 10, cv[sep_count]);
+		if (rc)
+			goto err;
+
+		++sep_count;
+	}
+
+	/* prevent underflow */
+	if (sep_count != ARRAY_SIZE(cv))
+		rc = -EBADMSG;
+
+err:
+	return rc;
+}
+
+enum header_opt {
+	ipe_header_policy_name = 0,
+	ipe_header_policy_version,
+	ipe_header_max
+};
+
+static const match_table_t header_tokens = {
+	{ipe_header_policy_name,	"policy_name=%s"},
+	{ipe_header_policy_version,	"policy_version=%s"},
+	{ipe_header_max,		NULL}
+};
+
+/**
+ * parse_header - Parse policy header information.
+ * @line: Supplies header line to be parsed.
+ * @p: Supplies the partial parsed policy.
+ *
+ * Return:
+ * * 0	- OK
+ * * !0	- Standard errno
+ */
+static int parse_header(char *line, struct ipe_parsed_policy *p)
+{
+	int rc = 0;
+	char *t, *ver = NULL;
+	substring_t args[MAX_OPT_ARGS];
+	size_t idx = 0;
+
+	while ((t = strsep(&line, " \t")) != NULL) {
+		int token;
+
+		if (*t == '\0')
+			continue;
+		if (idx >= ipe_header_max) {
+			rc = -EBADMSG;
+			goto err;
+		}
+
+		token = match_token(t, header_tokens, args);
+		if (token != idx) {
+			rc = -EBADMSG;
+			goto err;
+		}
+
+		switch (token) {
+		case ipe_header_policy_name:
+			p->name = match_strdup(&args[0]);
+			if (!p->name)
+				rc = -ENOMEM;
+			break;
+		case ipe_header_policy_version:
+			ver = match_strdup(&args[0]);
+			if (!ver) {
+				rc = -ENOMEM;
+				break;
+			}
+			rc = parse_version(ver, p);
+			break;
+		default:
+			rc = -EBADMSG;
+		}
+		if (rc)
+			goto err;
+		++idx;
+	}
+
+	if (idx != ipe_header_max) {
+		rc = -EBADMSG;
+		goto err;
+	}
+	goto out;
+
+err:
+	kfree(p->name);
+	p->name = NULL;
+out:
+	kfree(ver);
+	return rc;
+}
+
+/**
+ * is_default - Determine if the given token is "DEFAULT".
+ * @token: Supplies the token string to be compared.
+ *
+ * Return:
+ * * 0	- The token is not "DEFAULT"
+ * * !0	- The token is "DEFAULT"
+ */
+static bool is_default(char *token)
+{
+	return !strcmp(token, "DEFAULT");
+}
+
+/**
+ * free_rule - Free the supplied ipe_rule struct.
+ * @r: Supplies the ipe_rule struct to be freed.
+ */
+static void free_rule(struct ipe_rule *r)
+{
+	struct ipe_prop *p, *t;
+
+	if (IS_ERR_OR_NULL(r))
+		return;
+
+	list_for_each_entry_safe(p, t, &r->props, next) {
+		kfree(p);
+	}
+
+	kfree(r);
+}
+
+static const match_table_t operation_tokens = {
+	{ipe_op_exec,			"op=EXECUTE"},
+	{ipe_op_firmware,		"op=FIRMWARE"},
+	{ipe_op_kernel_module,		"op=KMODULE"},
+	{ipe_op_kexec_image,		"op=KEXEC_IMAGE"},
+	{ipe_op_kexec_initramfs,	"op=KEXEC_INITRAMFS"},
+	{ipe_op_ima_policy,		"op=IMA_POLICY"},
+	{ipe_op_ima_x509,		"op=IMA_X509_CERT"},
+	{ipe_op_max,			NULL}
+};
+
+/**
+ * parse_operation - Parse the opeartion type given a token string.
+ * @t: Supplies the token string to be parsed.
+ *
+ * Return: The parsed opeartion type.
+ */
+static enum ipe_op_type parse_operation(char *t)
+{
+	substring_t args[MAX_OPT_ARGS];
+
+	return match_token(t, operation_tokens, args);
+}
+
+static const match_table_t action_tokens = {
+	{ipe_action_allow,	"action=ALLOW"},
+	{ipe_action_deny,	"action=DENY"},
+	{ipe_action_max,	NULL}
+};
+
+/**
+ * parse_action - Parse the action type given a token string.
+ * @t: Supplies the token string to be parsed.
+ *
+ * Return: The parsed action type.
+ */
+static enum ipe_action_type parse_action(char *t)
+{
+	substring_t args[MAX_OPT_ARGS];
+
+	return match_token(t, action_tokens, args);
+}
+
+static const match_table_t property_tokens = {
+	{ipe_prop_max,					NULL}
+};
+
+/**
+ * parse_property - Parse the property type given a token string.
+ * @t: Supplies the token string to be parsed.
+ * @r: Supplies the ipe_rule the parsed property will be associated with.
+ *
+ * Return:
+ * * !IS_ERR	- OK
+ * * -ENOMEM	- Out of memory
+ * * -EBADMSG	- The supplied token cannot be parsed
+ */
+int parse_property(char *t, struct ipe_rule *r)
+{
+	substring_t args[MAX_OPT_ARGS];
+	struct ipe_prop *p = NULL;
+	int rc = 0;
+	int token;
+	char *dup = NULL;
+
+	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (!p) {
+		rc = -ENOMEM;
+		goto err;
+	}
+
+	token = match_token(t, property_tokens, args);
+
+	switch (token) {
+	case ipe_prop_max:
+	default:
+		rc = -EBADMSG;
+		break;
+	}
+	list_add_tail(&p->next, &r->props);
+
+err:
+	kfree(dup);
+	return rc;
+}
+
+/**
+ * parse_rule - parse a policy rule line.
+ * @line: Supplies rule line to be parsed.
+ * @p: Supplies the partial parsed policy.
+ *
+ * Return:
+ * * !IS_ERR	- OK
+ * * -ENOMEM	- Out of memory
+ * * -EBADMSG	- Policy syntax error
+ */
+static int parse_rule(char *line, struct ipe_parsed_policy *p)
+{
+	int rc = 0;
+	bool first_token = true, is_default_rule = false;
+	bool op_parsed = false;
+	enum ipe_op_type op = ipe_op_max;
+	enum ipe_action_type action = ipe_action_max;
+	struct ipe_rule *r = NULL;
+	char *t;
+
+	r = kzalloc(sizeof(*r), GFP_KERNEL);
+	if (!r) {
+		rc = -ENOMEM;
+		goto err;
+	}
+
+	INIT_LIST_HEAD(&r->next);
+	INIT_LIST_HEAD(&r->props);
+
+	while (t = strsep(&line, " \t"), line) {
+		if (*t == '\0')
+			continue;
+		if (first_token && is_default(t)) {
+			is_default_rule = true;
+		} else {
+			if (!op_parsed) {
+				op = parse_operation(t);
+				if (op == ipe_op_max)
+					rc = -EBADMSG;
+				else
+					op_parsed = true;
+			} else {
+				rc = parse_property(t, r);
+			}
+		}
+
+		if (rc)
+			goto err;
+		first_token = false;
+	}
+
+	action = parse_action(t);
+	if (action == ipe_action_max) {
+		rc = -EBADMSG;
+		goto err;
+	}
+
+	if (is_default_rule) {
+		if (op == ipe_op_max) {
+			if (p->global_default_action != ipe_action_max)
+				rc = -EBADMSG;
+			else
+				p->global_default_action = action;
+		} else {
+			if (p->rules[op].default_action != ipe_action_max)
+				rc = -EBADMSG;
+			else
+				p->rules[op].default_action = action;
+		}
+		free_rule(r);
+	} else if (op != ipe_op_max && action != ipe_action_max) {
+		r->op = op;
+		r->action = action;
+		list_add_tail(&r->next, &p->rules[op].rules);
+	} else {
+		rc = -EBADMSG;
+	}
+
+	if (rc)
+		goto err;
+
+	goto out;
+
+err:
+	free_rule(r);
+out:
+	return rc;
+}
+
+/**
+ * free_parsed_policy - free a parsed policy structure.
+ * @p: Supplies the parsed policy.
+ */
+void free_parsed_policy(struct ipe_parsed_policy *p)
+{
+	size_t i = 0;
+	struct ipe_rule *pp, *t;
+
+	if (IS_ERR_OR_NULL(p))
+		return;
+
+	for (i = 0; i < ARRAY_SIZE(p->rules); ++i)
+		list_for_each_entry_safe(pp, t, &p->rules[i].rules, next)
+			free_rule(pp);
+
+	kfree(p);
+}
+
+/**
+ * validate_policy - validate a parsed policy.
+ * @p: Supplies the fully parsed policy.
+ *
+ * Given a policy structure that was just parsed, validate that all
+ * necessary fields are present, initialized correctly, and all lines
+ * parsed are have been consumed.
+ *
+ * A parsed policy can be an invalid state for use (a default was
+ * undefined, a header was undefined) by just parsing the policy.
+ *
+ * Return:
+ * * 0		- OK
+ * * -EBADMSG	- Policy is invalid
+ */
+static int validate_policy(const struct ipe_parsed_policy *p)
+{
+	int i = 0;
+
+	if (p->global_default_action != ipe_action_max)
+		return 0;
+
+	for (i = 0; i < ARRAY_SIZE(p->rules); ++i) {
+		if (p->rules[i].default_action == ipe_action_max)
+			return -EBADMSG;
+	}
+
+	return 0;
+}
+
+/**
+ * parse_policy - Given a string, parse the string into an IPE policy.
+ * @p: partially filled ipe_policy structure to populate with the result.
+ *     it must have text and textlen set.
+ *
+ * Return:
+ * * 0		- OK
+ * * -EBADMSG	- Policy is invalid
+ * * -ENOMEM	- Out of Memory
+ */
+int parse_policy(struct ipe_policy *p)
+{
+	int rc = 0;
+	size_t len;
+	char *policy = NULL, *dup = NULL;
+	char *line = NULL;
+	bool header_parsed = false;
+	struct ipe_parsed_policy *pp = NULL;
+
+	if (!p->textlen)
+		return -EBADMSG;
+
+	policy = kmemdup_nul(p->text, p->textlen, GFP_KERNEL);
+	if (!policy)
+		return -ENOMEM;
+	dup = policy;
+
+	pp = new_parsed_policy();
+	if (IS_ERR(pp)) {
+		rc = PTR_ERR(pp);
+		goto out;
+	}
+
+	while ((line = strsep(&policy, "\n\r")) != NULL) {
+		remove_comment(line);
+		remove_trailing_spaces(line);
+		len = strlen(line);
+		if (!len)
+			continue;
+
+		if (!header_parsed) {
+			rc = parse_header(line, pp);
+			if (rc)
+				goto err;
+			header_parsed = true;
+			continue;
+		}
+
+		rc = parse_rule(line, pp);
+		if (rc)
+			goto err;
+	}
+
+	if (!header_parsed || validate_policy(pp)) {
+		rc = -EBADMSG;
+		goto err;
+	}
+
+	p->parsed = pp;
+
+	goto out;
+err:
+	free_parsed_policy(pp);
+out:
+	kfree(dup);
+
+	return rc;
+}
diff --git a/security/ipe/policy_parser.h b/security/ipe/policy_parser.h
new file mode 100644
index 000000000000..699ca58a5a32
--- /dev/null
+++ b/security/ipe/policy_parser.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+#ifndef IPE_POLICY_PARSER_H
+#define IPE_POLICY_PARSER_H
+
+int parse_policy(struct ipe_policy *p);
+void free_parsed_policy(struct ipe_parsed_policy *p);
+
+#endif /* IPE_POLICY_PARSER */
-- 
2.39.0