[PATCH v16 02/20] ipe: add policy parser

Fan Wu
2024-03-28T20:17:28Z

From: Deven Bowers <deven.desai@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@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 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
operation.
+ 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

v10:
+ Fix memory leaks in parser
+ Fix typos and change code styles

v11:
+ Fix code style issues

v12:
+ Add __always_unused to an unused parameter
+ Simplify error case handling

v13:
+ No changes

v14:
+ No changes

v15:
+ No changes

v16:
+ No changes
---
security/ipe/Makefile | 2 +
security/ipe/policy.c | 101 ++++++++
security/ipe/policy.h | 83 ++++++
security/ipe/policy_parser.c | 487 +++++++++++++++++++++++++++++++++++
security/ipe/policy_parser.h | 11 +
5 files changed, 684 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 f7a80d0f18f8..c09aec4904f2 100644
--- a/security/ipe/Makefile
+++ b/security/ipe/Makefile
@@ -7,3 +7,5 @@

obj-$(CONFIG_SECURITY_IPE) += \
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..f22a576a6d68
--- /dev/null
+++ b/security/ipe/policy.c
@@ -0,0 +1,101 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include <linux/errno.h>
+#include <linux/verification.h>
+
+#include "ipe.h"
+#include "policy.h"
+#include "policy_parser.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);
+ /*
+ * p->text is allocated only when p->pkcs7 is not NULL
+ * otherwise it points to the plaintext data inside the pkcs7
+ */
+ 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 __always_unused)
+{
+ 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.
+ *
+ * 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:
+ ipe_free_policy(new);
+ return ERR_PTR(rc);
+}
diff --git a/security/ipe/policy.h b/security/ipe/policy.h
new file mode 100644
index 000000000000..fb906f41522b
--- /dev/null
+++ b/security/ipe/policy.h
@@ -0,0 +1,83 @@
+/* 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_POLICY,
+ IPE_OP_X509,
+ __IPE_OP_MAX,
+};
+
+#define IPE_OP_INVALID __IPE_OP_MAX
+
+enum ipe_action_type {
+ IPE_ACTION_ALLOW = 0,
+ IPE_ACTION_DENY,
+ __IPE_ACTION_MAX
+};
+
+#define IPE_ACTION_INVALID __IPE_ACTION_MAX
+
+enum ipe_prop_type {
+ __IPE_PROP_MAX
+};
+
+#define IPE_PROP_INVALID __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..612839b405f4
--- /dev/null
+++ b/security/ipe/policy_parser.c
@@ -0,0 +1,487 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/parser.h>
+#include <linux/types.h>
+#include <linux/ctype.h>
+
+#include "policy.h"
+#include "policy_parser.h"
+
+#define START_COMMENT '#'
+#define IPE_POLICY_DELIM " \t"
+#define IPE_LINE_DELIM "\n\r"
+
+/**
+ * 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_INVALID;
+
+ for (i = 0; i < ARRAY_SIZE(p->rules); ++i) {
+ t = &p->rules[i];
+
+ t->default_action = IPE_ACTION_INVALID;
+ INIT_LIST_HEAD(&t->rules);
+ }
+
+ return p;
+}
+
+/**
+ * remove_comment - Truncate all chars following START_COMMENT in a string.
+ *
+ * @line: Supplies a policy line string for preprocessing.
+ */
+static void remove_comment(char *line)
+{
+ line = strchr(line, START_COMMENT);
+
+ if (line)
+ *line = '\0';
+}
+
+/**
+ * remove_trailing_spaces - Truncate all trailing spaces in a string.
+ *
+ * @line: Supplies a policy line string for preprocessing.
+ *
+ * Return: The length of truncated string.
+ */
+static size_t remove_trailing_spaces(char *line)
+{
+ size_t i = 0;
+
+ i = strlen(line);
+ while (i > 0 && isspace(line[i - 1]))
+ i--;
+
+ line[i] = '\0';
+
+ return i;
+}
+
+/**
+ * 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))
+ return -EBADMSG;
+
+ rc = kstrtou16(token, 10, cv[sep_count]);
+ if (rc)
+ return rc;
+
+ ++sep_count;
+ }
+
+ /* prevent underflow */
+ if (sep_count != ARRAY_SIZE(cv))
+ return -EBADMSG;
+
+ return 0;
+}
+
+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, IPE_POLICY_DELIM)) != NULL) {
+ int token;
+
+ if (*t == '\0')
+ continue;
+ if (idx >= __IPE_HEADER_MAX) {
+ rc = -EBADMSG;
+ goto out;
+ }
+
+ token = match_token(t, header_tokens, args);
+ if (token != idx) {
+ rc = -EBADMSG;
+ goto out;
+ }
+
+ 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 out;
+ ++idx;
+ }
+
+ if (idx != __IPE_HEADER_MAX)
+ rc = -EBADMSG;
+
+out:
+ kfree(ver);
+ return rc;
+}
+
+/**
+ * token_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 token_default(char *token)
+{
+ return !strcmp(token, "DEFAULT");
+}
+
+/**
+ * free_rule - Free the supplied ipe_rule struct.
+ * @r: Supplies the ipe_rule struct to be freed.
+ *
+ * Free a ipe_rule struct @r. Note @r must be removed from any lists before
+ * calling this function.
+ */
+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) {
+ list_del(&p->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_POLICY, "op=POLICY"},
+ {IPE_OP_X509, "op=X509_CERT"},
+ {IPE_OP_INVALID, NULL}
+};
+
+/**
+ * parse_operation - Parse the operation type given a token string.
+ * @t: Supplies the token string to be parsed.
+ *
+ * Return: The parsed operation 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_INVALID, 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);
+}
+
+/**
+ * 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
+ */
+static int parse_property(char *t, struct ipe_rule *r)
+{
+ return -EBADMSG;
+}
+
+/**
+ * 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_INVALID;
+ enum ipe_action_type action = IPE_ACTION_INVALID;
+ struct ipe_rule *r = NULL;
+ char *t;
+
+ r = kzalloc(sizeof(*r), GFP_KERNEL);
+ if (!r)
+ return -ENOMEM;
+
+ INIT_LIST_HEAD(&r->next);
+ INIT_LIST_HEAD(&r->props);
+
+ while (t = strsep(&line, IPE_POLICY_DELIM), line) {
+ if (*t == '\0')
+ continue;
+ if (first_token && token_default(t)) {
+ is_default_rule = true;
+ } else {
+ if (!op_parsed) {
+ op = parse_operation(t);
+ if (op == IPE_OP_INVALID)
+ 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_INVALID) {
+ rc = -EBADMSG;
+ goto err;
+ }
+
+ if (is_default_rule) {
+ if (!list_empty(&r->props)) {
+ rc = -EBADMSG;
+ } else if (op == IPE_OP_INVALID) {
+ if (p->global_default_action != IPE_ACTION_INVALID)
+ rc = -EBADMSG;
+ else
+ p->global_default_action = action;
+ } else {
+ if (p->rules[op].default_action != IPE_ACTION_INVALID)
+ rc = -EBADMSG;
+ else
+ p->rules[op].default_action = action;
+ }
+ } else if (op != IPE_OP_INVALID && action != IPE_ACTION_INVALID) {
+ r->op = op;
+ r->action = action;
+ } else {
+ rc = -EBADMSG;
+ }
+
+ if (rc)
+ goto err;
+ if (!is_default_rule)
+ list_add_tail(&r->next, &p->rules[op].rules);
+ else
+ free_rule(r);
+
+ return rc;
+err:
+ free_rule(r);
+ 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) {
+ list_del(&pp->next);
+ free_rule(pp);
+ }
+
+ kfree(p->name);
+ 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.
+ *
+ * A parsed policy can be in an invalid state for use (a default was
+ * undefined) by just parsing the policy.
+ *
+ * Return:
+ * * 0 - OK
+ * * -EBADMSG - Policy is invalid
+ */
+static int validate_policy(const struct ipe_parsed_policy *p)
+{
+ size_t i = 0;
+
+ if (p->global_default_action != IPE_ACTION_INVALID)
+ return 0;
+
+ for (i = 0; i < ARRAY_SIZE(p->rules); ++i) {
+ if (p->rules[i].default_action == IPE_ACTION_INVALID)
+ 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, IPE_LINE_DELIM)) != NULL) {
+ remove_comment(line);
+ len = remove_trailing_spaces(line);
+ if (!len)
+ continue;
+
+ if (!header_parsed) {
+ rc = parse_header(line, pp);
+ if (rc)
+ goto err;
+ header_parsed = true;
+ } else {
+ rc = parse_rule(line, pp);
+ if (rc)
+ goto err;
+ }
+ }
+
+ if (!header_parsed || validate_policy(pp)) {
+ rc = -EBADMSG;
+ goto err;
+ }
+
+ p->parsed = pp;
+
+out:
+ kfree(dup);
+ return rc;
+err:
+ free_parsed_policy(pp);
+ goto out;
+}
diff --git a/security/ipe/policy_parser.h b/security/ipe/policy_parser.h
new file mode 100644
index 000000000000..2b744103d06a
--- /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_H */
--
2.44.0