[RFC PATCH v9 02/16] ipe: add policy parser
Roberto Sassu
roberto.sassu at huaweicloud.com
Tue Jan 31 10:53:27 UTC 2023
On Mon, 2023-01-30 at 14:57 -0800, Fan Wu wrote:
> 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;
> + }
Uhm, memory leak? Also below. I suggest to use kmemleak.
Roberto
> +
> + 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 */
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