RE: [RFC PATCH v7 14/16] scripts: add boot policy generation program

Roberto Sassu
2021-11-03T16:43:20Z

> From: deven.desai@linux.microsoft.com
> [mailto:deven.desai@linux.microsoft.com]
> From: Deven Bowers <deven.desai@linux.microsoft.com>
>
> Enables an IPE policy to be enforced from kernel start, enabling access
> control based on trust from kernel startup. This is accomplished by
> transforming an IPE policy indicated by CONFIG_IPE_BOOT_POLICY into a
> c-string literal that is parsed at kernel startup as an unsigned policy.
>
> Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>
> ---
>
> Relevant changes since v6:
> * Move patch 01/12 to [14/16] of the series
>
> ---
> MAINTAINERS | 1 +
> scripts/Makefile | 1 +
> scripts/ipe/Makefile | 2 +
> scripts/ipe/polgen/.gitignore | 1 +
> scripts/ipe/polgen/Makefile | 6 ++
> scripts/ipe/polgen/polgen.c | 145 ++++++++++++++++++++++++++++++++++
> security/ipe/.gitignore | 1 +
> security/ipe/Kconfig | 10 +++
> security/ipe/Makefile | 13 +++
> security/ipe/ctx.c | 18 +++++
> 10 files changed, 198 insertions(+)
> create mode 100644 scripts/ipe/Makefile
> create mode 100644 scripts/ipe/polgen/.gitignore
> create mode 100644 scripts/ipe/polgen/Makefile
> create mode 100644 scripts/ipe/polgen/polgen.c
> create mode 100644 security/ipe/.gitignore
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f1e76f791d47..a84ca781199b 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -9283,6 +9283,7 @@ INTEGRITY POLICY ENFORCEMENT (IPE)
> M: Deven Bowers <deven.desai@linux.microsoft.com>
> M: Fan Wu <wufan@linux.microsoft.com>
> S: Supported
> +F: scripts/ipe/
> F: security/ipe/
>
> INTEL 810/815 FRAMEBUFFER DRIVER
> diff --git a/scripts/Makefile b/scripts/Makefile
> index 9adb6d247818..a31da6d57a36 100644
> --- a/scripts/Makefile
> +++ b/scripts/Makefile
> @@ -41,6 +41,7 @@ targets += module.lds
> subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
> subdir-$(CONFIG_MODVERSIONS) += genksyms
> subdir-$(CONFIG_SECURITY_SELINUX) += selinux
> +subdir-$(CONFIG_SECURITY_IPE) += ipe
>
> # Let clean descend into subdirs
> subdir- += basic dtc gdb kconfig mod
> diff --git a/scripts/ipe/Makefile b/scripts/ipe/Makefile
> new file mode 100644
> index 000000000000..e87553fbb8d6
> --- /dev/null
> +++ b/scripts/ipe/Makefile
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +subdir-y := polgen
> diff --git a/scripts/ipe/polgen/.gitignore b/scripts/ipe/polgen/.gitignore
> new file mode 100644
> index 000000000000..80f32f25d200
> --- /dev/null
> +++ b/scripts/ipe/polgen/.gitignore
> @@ -0,0 +1 @@
> +polgen
> diff --git a/scripts/ipe/polgen/Makefile b/scripts/ipe/polgen/Makefile
> new file mode 100644
> index 000000000000..066060c22b4a
> --- /dev/null
> +++ b/scripts/ipe/polgen/Makefile
> @@ -0,0 +1,6 @@
> +# SPDX-License-Identifier: GPL-2.0
> +hostprogs-always-y := polgen
> +HOST_EXTRACFLAGS += \
> + -I$(srctree)/include \
> + -I$(srctree)/include/uapi \
> +
> diff --git a/scripts/ipe/polgen/polgen.c b/scripts/ipe/polgen/polgen.c
> new file mode 100644
> index 000000000000..73cf13e743f7
> --- /dev/null
> +++ b/scripts/ipe/polgen/polgen.c
> @@ -0,0 +1,145 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) Microsoft Corporation. All rights reserved.
> + */
> +
> +#include <stdlib.h>
> +#include <stddef.h>
> +#include <stdio.h>
> +#include <unistd.h>
> +#include <errno.h>
> +
> +static void usage(const char *const name)
> +{
> + printf("Usage: %s OutputFile (PolicyFile)\n", name);
> + exit(EINVAL);
> +}
> +
> +static int policy_to_buffer(const char *pathname, char **buffer, size_t *size)
> +{
> + int rc = 0;
> + FILE *fd;
> + char *lbuf;
> + size_t fsize;
> + size_t read;
> +
> + fd = fopen(pathname, "r");
> + if (!fd) {
> + rc = errno;
> + goto out;
> + }
> +
> + fseek(fd, 0, SEEK_END);
> + fsize = ftell(fd);
> + rewind(fd);
> +
> + lbuf = malloc(fsize);
> + if (!lbuf) {
> + rc = ENOMEM;
> + goto out_close;
> + }
> +
> + read = fread((void *)lbuf, sizeof(*lbuf), fsize, fd);
> + if (read != fsize) {
> + rc = -1;
> + goto out_free;
> + }
> +
> + *buffer = lbuf;
> + *size = fsize;
> + fclose(fd);
> +
> + return rc;
> +
> +out_free:
> + free(lbuf);
> +out_close:
> + fclose(fd);
> +out:
> + return rc;
> +}
> +
> +static int write_boot_policy(const char *pathname, const char *buf, size_t size)
> +{
> + int rc = 0;
> + FILE *fd;
> + size_t i;
> +
> + fd = fopen(pathname, "w");
> + if (!fd) {
> + rc = errno;
> + goto err;
> + }
> +
> + fprintf(fd, "/* This file is automatically generated.");
> + fprintf(fd, " Do not edit. */\n");
> + fprintf(fd, "#include <stddef.h>\n");
> + fprintf(fd, "\nextern const char *const ipe_boot_policy;\n\n");
> + fprintf(fd, "const char *const ipe_boot_policy =\n");
> +
> + if (!buf || size == 0) {
> + fprintf(fd, "\tNULL;\n");
> + fclose(fd);
> + return 0;
> + }
> +
> + fprintf(fd, "\t\"");
> +
> + for (i = 0; i < size; ++i) {
> + switch (buf[i]) {
> + case '"':
> + fprintf(fd, "\\\"");
> + break;
> + case '\'':
> + fprintf(fd, "'");
> + break;
> + case '\n':
> + fprintf(fd, "\\n\"\n\t\"");
> + break;
> + case '\\':
> + fprintf(fd, "\\\\");
> + break;
> + case '\t':
> + fprintf(fd, "\\t");
> + break;
> + case '\?':
> + fprintf(fd, "\\?");
> + break;
> + default:
> + fprintf(fd, "%c", buf[i]);
> + }
> + }
> + fprintf(fd, "\";\n");
> + fclose(fd);
> +
> + return 0;
> +
> +err:
> + if (fd)
> + fclose(fd);
> + return rc;
> +}
> +
> +int main(int argc, const char *const argv[])
> +{
> + int rc = 0;
> + size_t len = 0;
> + char *policy = NULL;
> +
> + if (argc < 2)
> + usage(argv[0]);
> +
> + if (argc > 2) {
> + rc = policy_to_buffer(argv[2], &policy, &len);
> + if (rc != 0)
> + goto cleanup;
> + }
> +
> + rc = write_boot_policy(argv[1], policy, len);
> +cleanup:
> + if (policy)
> + free(policy);
> + if (rc != 0)
> + perror("An error occurred during policy conversion: ");
> + return rc;
> +}
> diff --git a/security/ipe/.gitignore b/security/ipe/.gitignore
> new file mode 100644
> index 000000000000..eca22ad5ed22
> --- /dev/null
> +++ b/security/ipe/.gitignore
> @@ -0,0 +1 @@
> +boot-policy.c
> \ No newline at end of file
> diff --git a/security/ipe/Kconfig b/security/ipe/Kconfig
> index fcf82a8152ec..39df680b67a2 100644
> --- a/security/ipe/Kconfig
> +++ b/security/ipe/Kconfig
> @@ -20,6 +20,16 @@ menuconfig SECURITY_IPE
>
> if SECURITY_IPE
>
> +config IPE_BOOT_POLICY
> + string "Integrity policy to apply on system startup"
> + help
> + This option specifies a filepath to a IPE policy that is compiled
> + into the kernel. This policy will be enforced until a policy update
> + is deployed via the $securityfs/ipe/policies/$policy_name/active
> + interface.
> +
> + If unsure, leave blank.
> +
> choice
> prompt "Hash algorithm used in auditing policies"
> default IPE_AUDIT_HASH_SHA1
> diff --git a/security/ipe/Makefile b/security/ipe/Makefile
> index 1e7b2d7fcd9e..89fec670f954 100644
> --- a/security/ipe/Makefile
> +++ b/security/ipe/Makefile
> @@ -7,7 +7,18 @@
>
> ccflags-y := -I$(srctree)/security/ipe/modules
>
> +quiet_cmd_polgen = IPE_POL $(2)
> + cmd_polgen = scripts/ipe/polgen/polgen security/ipe/boot-policy.c $(2)
> +
> +$(eval $(call config_filename,IPE_BOOT_POLICY))
> +
> +targets += boot-policy.c
> +
> +$(obj)/boot-policy.c: scripts/ipe/polgen/polgen
> $(IPE_BOOT_POLICY_FILENAME) FORCE
> + $(call if_changed,polgen,$(IPE_BOOT_POLICY_FILENAME))
> +
> obj-$(CONFIG_SECURITY_IPE) += \
> + boot-policy.o \
> ctx.o \
> eval.o \
> fs.o \
> @@ -21,3 +32,5 @@ obj-$(CONFIG_SECURITY_IPE) += \
> policyfs.o \
>
> obj-$(CONFIG_AUDIT) += audit.o
> +
> +clean-files := boot-policy.c \
> diff --git a/security/ipe/ctx.c b/security/ipe/ctx.c
> index fc9b8e467bc9..879acf4ceac5 100644
> --- a/security/ipe/ctx.c
> +++ b/security/ipe/ctx.c
> @@ -15,6 +15,7 @@
> #include <linux/spinlock.h>
> #include <linux/moduleparam.h>
>
> +extern const char *const ipe_boot_policy;
> static bool success_audit;
> static bool enforce = true;
>
> @@ -329,6 +330,7 @@ void ipe_put_ctx(struct ipe_context *ctx)
> int __init ipe_init_ctx(void)
> {
> int rc = 0;
> + struct ipe_policy *p = NULL;
> struct ipe_context *lns = NULL;
>
> lns = create_ctx();
> @@ -342,10 +344,26 @@ int __init ipe_init_ctx(void)
> WRITE_ONCE(lns->enforce, enforce);
> spin_unlock(&lns->lock);
>
> + if (ipe_boot_policy) {
> + p = ipe_new_policy(ipe_boot_policy, strlen(ipe_boot_policy),
> + NULL, 0);
> + if (IS_ERR(p)) {
> + rc = PTR_ERR(lns);

This should be:

rc = PTR_ERR(p);

> + goto err;
> + }
> +
> + ipe_add_policy(lns, p);
> + rc = ipe_set_active_pol(p);
> + if (!rc)

Here you need to set a non-zero value, so that ipe_init()
does not enable the LSM.

I would set to 1 a new global variable, like ipe_lsm_enabled,
in ipe_init() just before security_add_hooks().

Then, I would add a check of this variable in ipe_init_securityfs()
to avoid the kernel panic.

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Zhong Ronghua

> + goto err;
> + }
> +
> rcu_assign_pointer(*ipe_tsk_ctx(current), lns);
> + ipe_put_policy(p);
>
> return 0;
> err:
> + ipe_put_policy(p);
> ipe_put_ctx(lns);
> return rc;
> }
> --
> 2.33.0