common/rollback: Add support for rollback protection

Implement actual rollback protection. First, we add a new field
in the version structure, which is an incrementing integer
(we'll start by shipping images with version 0, and gradually
increase the number as required). This allows us to release
new versions of the EC without necessarily bumping the rollback
protection.

For the rollback protection block itself, it contains 2 sub-blocks
of equal size (normally, 2k), that are individually erasable.
The rollback code looks at both, and takes the most restrictive one
to determine the desired rollback minimum version. The blocks
are also allowed to be erased (full of 1's), in which case the
rollback minimum version is assumed to be 0.

We also add an FMAP entry, in case we later decide to allow the
signer to increment the rollback version.

Also note that, like any version_data struct change, this change
breaks compatibility between old and new RO/RW.

Follow-up code will take care of auto-updating the rollback block
as required, and properly manage block protection.

BRANCH=none
BUG=b:35586219
TEST=Flash hammer
     rollbackinfo => 1 version 0 block, 1 empty block, RW verifies
           correctly.
     rollbackupdate 0; rollbackinfo => No change
     rollbackupdate 1; reboot => RO refuses to jump to RW
     rollbackupdate 2, 3, 4; rollbackinfo => Writes alternate
           between the 2 blocks.
     rollbackupdate 2 => Refuses to downgrade version

Change-Id: Ia969afb481a93deb912b9153bdd95ace01ad8fa7
Reviewed-on: https://chromium-review.googlesource.com/452815
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

common/build.mk

@@ -78,6 +78,7 @@ common-$(CONFIG_PSTORE)+=pstore_commands.o
 common-$(CONFIG_PWM)+=pwm.o
 common-$(CONFIG_PWM_KBLIGHT)+=pwm_kblight.o
 common-$(CONFIG_RSA)+=rsa.o
+common-$(CONFIG_ROLLBACK)+=rollback.o
 common-$(CONFIG_RWSIG)+=rwsig.o
 common-$(CONFIG_MATH_UTIL)+=math_util.o
 common-$(CONFIG_SHA1)+= sha1.o

common/firmware_image.S

@@ -7,6 +7,7 @@
  */
 
 #include "config.h"
+#include "rollback.h"
 
 #define FW_FILE(builddir,proj,sect,suffix,ext) \
 	builddir##/##sect##/##proj##.##sect##suffix##.flat##ext
@@ -29,6 +30,13 @@
 .incbin STRINGIFY(FINAL_OUTDIR/key.vbpubk2)
 #endif
 
+#ifdef CONFIG_ROLLBACK
+/* Note: matches struct rollback_data in common/rollback.c. */
+.section .image.ROLLBACK, "a"
+.long CONFIG_ROLLBACK_VERSION
+.long CROS_EC_ROLLBACK_COOKIE
+#endif
+
 /* Shared objects library */
 #ifdef CONFIG_SHAREDLIB
 .section .image.libsharedobjs, "ax"

common/firmware_image.lds.S

@@ -33,6 +33,12 @@ SECTIONS
     } > FLASH =0xff
 #endif
 
+#ifdef CONFIG_ROLLBACK
+    .image.ROLLBACK : AT(CONFIG_PROGRAM_MEMORY_BASE + CONFIG_ROLLBACK_OFF) {
+        *(.image.ROLLBACK)
+    } > FLASH =0xff
+#endif
+
 #ifdef CONFIG_SHAREDLIB
     .image.libsharedobjs : AT(CONFIG_PROGRAM_MEMORY_BASE + \
                               CONFIG_SHAREDLIB_MEM_OFF) {

common/fmap.c

@@ -63,11 +63,21 @@ struct fmap_area_header {
 } __packed;
 
 #ifdef CONFIG_RWSIG_TYPE_RWSIG
-#define NUM_EC_FMAP_AREAS 9
+#define NUM_EC_FMAP_AREAS_RWSIG 2
 #else
-#define NUM_EC_FMAP_AREAS 7
+#define NUM_EC_FMAP_AREAS_RWSIG 0
 #endif
 
+#ifdef CONFIG_ROLLBACK
+#define NUM_EC_FMAP_AREAS_ROLLBACK 1
+#else
+#define NUM_EC_FMAP_AREAS_ROLLBACK 0
+#endif
+
+#define NUM_EC_FMAP_AREAS (7 + \
+			NUM_EC_FMAP_AREAS_RWSIG + \
+			NUM_EC_FMAP_AREAS_ROLLBACK)
+
 const struct _ec_fmap {
 	struct fmap_header header;
 	struct fmap_area_header area[NUM_EC_FMAP_AREAS];
@@ -178,6 +188,24 @@ const struct _ec_fmap {
 			.area_size = sizeof(current_image_data.version),
 			.area_flags = FMAP_AREA_STATIC,
 		},
+#ifdef CONFIG_ROLLBACK
+		{
+			/*
+			 * RW rollback version, 32-bit unsigned integer.
+			 * TODO: Get the relative offset of
+			 * __image_data_offset within our RW image to
+			 * accommodate image asymmetry.
+			 */
+			.area_name = "RW_RBVER",
+			.area_offset = CONFIG_EC_WRITABLE_STORAGE_OFF -
+				FMAP_REGION_START + CONFIG_RW_STORAGE_OFF +
+				RELATIVE_RO((uint32_t)__image_data_offset) +
+				offsetof(struct image_data, rollback_version),
+			.area_size = sizeof(
+				current_image_data.rollback_version),
+			.area_flags = FMAP_AREA_STATIC,
+		},
+#endif
 #ifdef CONFIG_RWSIG_TYPE_RWSIG
 		{
 			 /* RW image signature */

common/rollback.c

@@ -0,0 +1,179 @@
+/* Copyright 2017 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Rollback protection logic. */
+
+#include "common.h"
+#include "console.h"
+#include "flash.h"
+#include "rollback.h"
+#include "system.h"
+#include "util.h"
+
+/* Number of rollback regions */
+#define ROLLBACK_REGIONS 2
+
+/*
+ * Note: Do not change this structure without also updating
+ * common/firmware_image.S .image.ROLLBACK section.
+ */
+struct rollback_data {
+	int32_t rollback_min_version;
+	uint32_t cookie;
+};
+
+/* We need at least 2 erasable blocks in the rollback region. */
+BUILD_ASSERT(CONFIG_ROLLBACK_SIZE >= ROLLBACK_REGIONS*CONFIG_FLASH_ERASE_SIZE);
+BUILD_ASSERT(sizeof(struct rollback_data) <= CONFIG_FLASH_ERASE_SIZE);
+
+static uintptr_t get_rollback_offset(int region)
+{
+	return CONFIG_ROLLBACK_OFF + region * CONFIG_FLASH_ERASE_SIZE;
+}
+
+static int read_rollback(int region, struct rollback_data *data)
+{
+	uintptr_t offset;
+
+	offset = get_rollback_offset(region);
+
+	if (flash_read(offset, sizeof(*data), (char *)data))
+		return EC_ERROR_UNKNOWN;
+
+	return EC_SUCCESS;
+}
+
+/*
+ * Get the most recent rollback information.
+ *
+ * @rollback_min_version: Minimum version to accept for rollback protection,
+ *                        or 0 if no rollback information is present.
+ *
+ * Return most recent region index on success (>= 0, or 0 if no rollback
+ * region is valid), negative value on error.
+ */
+static int get_latest_rollback(int32_t *rollback_min_version)
+{
+	int region;
+	int min_region = 0;
+
+	*rollback_min_version = 0;
+
+	for (region = 0; region < ROLLBACK_REGIONS; region++) {
+		struct rollback_data data;
+
+		if (read_rollback(region, &data))
+			return -1;
+
+		/* Check if not initialized or invalid cookie. */
+		if (data.cookie != CROS_EC_ROLLBACK_COOKIE)
+			continue;
+
+		if (data.rollback_min_version > *rollback_min_version) {
+			min_region = region;
+			*rollback_min_version = data.rollback_min_version;
+		}
+	}
+
+	return min_region;
+}
+
+int32_t rollback_get_minimum_version(void)
+{
+	int32_t rollback_min_version;
+
+	if (get_latest_rollback(&rollback_min_version) < 0)
+		return -1;
+
+	return rollback_min_version;
+}
+
+int rollback_update(int32_t next_min_version)
+{
+	struct rollback_data data;
+	uintptr_t offset;
+	int region;
+	int32_t current_min_version;
+	int ret;
+
+	region = get_latest_rollback(&current_min_version);
+
+	if (region < 0)
+		return EC_ERROR_UNKNOWN;
+
+	/* Do not accept to decrement the value. */
+	if (next_min_version < current_min_version)
+		return EC_ERROR_INVAL;
+
+	/* No need to update if version is already correct. */
+	if (next_min_version == current_min_version)
+		return EC_SUCCESS;
+
+	/* Use the other region. */
+	region = (region + 1) % ROLLBACK_REGIONS;
+
+	offset = get_rollback_offset(region);
+
+	data.rollback_min_version = next_min_version;
+	data.cookie = CROS_EC_ROLLBACK_COOKIE;
+
+	if (system_unsafe_to_overwrite(offset, CONFIG_FLASH_ERASE_SIZE))
+		return EC_ERROR_ACCESS_DENIED;
+
+	ret = flash_erase(offset, CONFIG_FLASH_ERASE_SIZE);
+	if (ret)
+		return ret;
+
+	return flash_write(offset, sizeof(data), (char *)&data);
+}
+
+static int command_rollback_info(int argc, char **argv)
+{
+	int region, ret, min_region;
+	int32_t rollback_min_version;
+
+	min_region = get_latest_rollback(&rollback_min_version);
+
+	if (min_region < 0)
+		return EC_ERROR_UNKNOWN;
+
+	ccprintf("rollback minimum version: %d\n", rollback_min_version);
+
+	for (region = 0; region < ROLLBACK_REGIONS; region++) {
+		struct rollback_data data;
+
+		ret = read_rollback(region, &data);
+		if (ret)
+			return ret;
+
+		ccprintf("rollback %d: %08x %08x%s\n",
+			region, data.rollback_min_version, data.cookie,
+			min_region == region ? " *" : "");
+	}
+
+	return EC_SUCCESS;
+}
+DECLARE_SAFE_CONSOLE_COMMAND(rollbackinfo, command_rollback_info,
+			     NULL,
+			     "Print rollback info");
+
+static int command_rollback_update(int argc, char **argv)
+{
+	int32_t min_version;
+	char *e;
+
+	if (argc < 2)
+		return EC_ERROR_PARAM_COUNT;
+
+	min_version = strtoi(argv[1], &e, 0);
+
+	if (*e || min_version < 0)
+		return EC_ERROR_PARAM1;
+
+	return rollback_update(min_version);
+}
+DECLARE_CONSOLE_COMMAND(rollbackupdate, command_rollback_update,
+			"min_version",
+			"Update rollback info");

common/rwsig.c

@@ -9,6 +9,7 @@
 
 #include "console.h"
 #include "ec_commands.h"
+#include "rollback.h"
 #include "rsa.h"
 #include "sha256.h"
 #include "shared_mem.h"
@@ -16,6 +17,7 @@
 #include "usb_pd.h"
 #include "util.h"
 #include "vb21_struct.h"
+#include "version.h"
 
 /* Console output macros */
 #define CPRINTF(format, args...) cprintf(CC_SYSTEM, format, ## args)
@@ -63,6 +65,10 @@ void check_rw_signature(void)
 	const struct vb21_packed_key *vb21_key;
 	const struct vb21_signature *vb21_sig;
 #endif
+#ifdef CONFIG_ROLLBACK
+	int32_t rw_rollback_version;
+	int32_t min_rollback_version;
+#endif
 
 	/* Only the Read-Only firmware needs to do the signature check */
 	if (system_get_image_copy() != SYSTEM_IMAGE_RO)
@@ -74,6 +80,18 @@ void check_rw_signature(void)
 
 	CPRINTS("Verifying RW image...");
 
+#ifdef CONFIG_ROLLBACK
+	rw_rollback_version = system_get_rollback_version(SYSTEM_IMAGE_RW);
+	min_rollback_version = rollback_get_minimum_version();
+
+	if (rw_rollback_version < 0 || min_rollback_version < 0 ||
+	    rw_rollback_version < min_rollback_version) {
+		CPRINTS("Rollback error (%d < %d)",
+			rw_rollback_version, min_rollback_version);
+		return;
+	}
+#endif
+
 	/* Large buffer for RSA computation : could be re-use afterwards... */
 	res = shared_mem_acquire(3 * RSANUMBYTES, (char **)&rsa_workbuf);
 	if (res) {

common/system.c

@@ -617,6 +617,15 @@ const char *system_get_version(enum system_image_copy_t copy)
 	return data ? data->version : "";
 }
 
+#ifdef CONFIG_ROLLBACK
+int32_t system_get_rollback_version(enum system_image_copy_t copy)
+{
+	const struct image_data *data = system_get_image_data(copy);
+
+	return data ? data->rollback_version : -1;
+}
+#endif
+
 int system_get_image_used(enum system_image_copy_t copy)
 {
 	const struct image_data *data = system_get_image_data(copy);

common/version.c

@@ -7,9 +7,13 @@
 
 #include <stdint.h>
 #include "common.h"
+#include "compile_time_macros.h"
 #include "ec_version.h"
 #include "version.h"
 
+BUILD_ASSERT(CONFIG_ROLLBACK_VERSION >= 0);
+BUILD_ASSERT(CONFIG_ROLLBACK_VERSION <= INT32_MAX);
+
 const struct image_data __keep current_image_data
 	__attribute__((section(".rodata.ver"))) = {
 	.cookie1 = CROS_EC_IMAGE_DATA_COOKIE1,
@@ -17,6 +21,7 @@ const struct image_data __keep current_image_data
 #ifndef TEST_BUILD
 	.size = (const uintptr_t)&__image_size,
 #endif
+	.rollback_version = CONFIG_ROLLBACK_VERSION,
 	.cookie2 = CROS_EC_IMAGE_DATA_COOKIE2,
 };
 

include/config.h

@@ -1131,6 +1131,17 @@
 #undef CONFIG_ROLLBACK_OFF
 #undef CONFIG_ROLLBACK_SIZE
 
+/*
+ * Current rollback version. Meaningless for RO (but provides the minimum value
+ * that will be written to the rollback protection at flash time).
+ *
+ * For RW, rollback version included in version structure, used by RO to
+ * determine if the RW image is recent enough and can be jumped to.
+ *
+ * Valid values are >= 0, <= INT32_MAX (positive, 32-bit signed integer).
+ */
+#define CONFIG_ROLLBACK_VERSION 0
+
 /*
  * Board Image ec.bin contains a RO firmware.  If not defined, the image will
  * only contain the RW firmware. The RO firmware comes from another board.

include/rollback.h

@@ -0,0 +1,32 @@
+/* Copyright 2017 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef __CROS_EC_ROLLBACK_H
+#define __CROS_EC_ROLLBACK_H
+
+#define CROS_EC_ROLLBACK_COOKIE 0x0b112233
+
+#ifndef __ASSEMBLER__
+
+/**
+ * Get minimum version set by rollback protection blocks.
+ *
+ * @return Minimum rollback version, 0 if neither block is initialized,
+ * negative value on error.
+ */
+int rollback_get_minimum_version(void);
+
+/**
+ * Update rollback protection block to the version passed as parameter.
+ *
+ * @param next_min_version	Minimum version to write in rollback block.
+ *
+ * @return EC_SUCCESS on success, EC_ERROR_* on error.
+ */
+int rollback_update(int32_t next_min_version);
+
+#endif
+
+#endif  /* __CROS_EC_ROLLBACK_H */

include/system.h

@@ -193,6 +193,15 @@ int system_get_image_used(enum system_image_copy_t copy);
  */
 int system_run_image_copy(enum system_image_copy_t copy);
 
+/**
+ * Get the rollback version for an image
+ *
+ * @param copy		Image copy to get version from, or SYSTEM_IMAGE_UNKNOWN
+ *			to get the version for the currently running image.
+ * @return The rollback version, negative value on error.
+ */
+int32_t system_get_rollback_version(enum system_image_copy_t copy);
+
 /**
  * Get the version string for an image
  *

include/version.h

@@ -11,12 +11,13 @@
 #include "common.h"
 
 #define CROS_EC_IMAGE_DATA_COOKIE1 0xce778899
-#define CROS_EC_IMAGE_DATA_COOKIE2 0xceaabbcc
+#define CROS_EC_IMAGE_DATA_COOKIE2 0xceaabbdd
 
 struct image_data {
 	uint32_t cookie1;
 	char version[32];
 	uint32_t size;
+	int32_t rollback_version;
 	uint32_t cookie2;
 } __packed;