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

Deven Bowers <deven.desai@xxxxxxxxxxxxxxxxxxx> · Thu, 4 Nov 2021 09:52:35 -0700

On 11/3/2021 9:53 AM, Roberto Sassu wrote:
From: Roberto Sassu [mailto:roberto.sassu@xxxxxxxxxx]
Sent: Wednesday, November 3, 2021 5:43 PM
From: deven.desai@xxxxxxxxxxxxxxxxxxx
[mailto:deven.desai@xxxxxxxxxxxxxxxxxxx]
From: Deven Bowers <deven.desai@xxxxxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxx>
---

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@xxxxxxxxxxxxxxxxxxx>
  M:	Fan Wu <wufan@xxxxxxxxxxxxxxxxxxx>
  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.
Actually you probably should just check that rc is not zero
and goto err.

Roberto

Yeah, I actually noticed these two mistakes myself fairly recently.

Changes will be applied in v8.

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.

That's my plan.

-Deven






