[RFC PATCH 1/1] image: add anti rollback protection for FIT Images

Thirupathaiah Annapureddy
2020-09-01T20:48:15Z

Anti rollback protection is required when there is a need to retire
previous versions of FIT images due to security flaws in them.
Currently U-Boot Verified boot does not have rollback protection to
protect against known security flaws.

This change adds anti-rollback protection for FIT images.

Signed-off-by: Thirupathaiah Annapureddy <thiruan@linux.microsoft.com>
---
Kconfig | 9 +++++
common/image-fit-sig.c | 79 ++++++++++++++++++++++++++++++++++++++++++
common/image-fit.c | 24 +++++++++++++
include/image.h | 23 ++++++++++++
4 files changed, 135 insertions(+)

diff --git a/Kconfig b/Kconfig
index 883e3f71d0..3959a6592c 100644
--- a/Kconfig
+++ b/Kconfig
@@ -533,6 +533,15 @@ config FIT_CIPHER
Enable the feature of data ciphering/unciphering in the tool mkimage
and in the u-boot support of the FIT image.

+config FIT_ARBP
+ bool "Enable Anti rollback version check for FIT images"
+ depends on FIT_SIGNATURE
+ default n
+ help
+ Enable this to activate anti-rollback protection. This is required
+ when a platform needs to retire previous versions of FIT images due to
+ security flaws in in them.
+
config FIT_VERBOSE
bool "Show verbose messages when FIT images fail"
help
diff --git a/common/image-fit-sig.c b/common/image-fit-sig.c
index cc1967109e..5103508894 100644
--- a/common/image-fit-sig.c
+++ b/common/image-fit-sig.c
@@ -78,6 +78,35 @@ struct image_region *fit_region_make_list(const void *fit,
return region;
}

+#if !defined(USE_HOSTCC)
+static int fit_image_verify_arbvn(const void *fit, int image_noffset)
+{
+ uint8_t type;
+ uint32_t image_arbvn;
+ uint32_t plat_arbvn = 0;
+ int ret;
+
+ ret = fit_image_get_arbvn(fit, image_noffset, &image_arbvn);
+ if (ret)
+ return 0;
+
+ ret = fit_image_get_type(fit, image_noffset, &type);
+ if (ret)
+ return 0;
+
+ ret = board_get_arbvn(type, &plat_arbvn);
+
+ if (image_arbvn < plat_arbvn) {
+ return -EPERM;
+ } else if (image_arbvn > plat_arbvn) {
+ ret = board_set_arbvn(type, image_arbvn);
+ return ret;
+ }
+
+ return 0;
+}
+#endif
+
static int fit_image_setup_verify(struct image_sign_info *info,
const void *fit, int noffset,
int required_keynode, char **err_msgp)
@@ -181,6 +210,14 @@ static int fit_image_verify_sig(const void *fit, int image_noffset,
goto error;
}

+#if !defined(USE_HOSTCC)
+ if (IMAGE_ENABLE_ARBP && verified) {
+ ret = fit_image_verify_arbvn(fit, image_noffset);
+ if (ret)
+ verified = 0;
+ }
+#endif
+
return verified ? 0 : -EPERM;

error:
@@ -370,6 +407,40 @@ static int fit_config_check_sig(const void *fit, int noffset,
return 0;
}

+#if !defined(USE_HOSTCC)
+static int fit_config_verify_arbvn(const void *fit, int conf_noffset,
+ int sig_offset)
+{
+ static const char default_list[] = FIT_KERNEL_PROP "\0"
+ FIT_FDT_PROP;
+ int ret, len;
+ const char *prop, *iname, *end;
+ int image_noffset;
+
+ /* If there is "sign-images" property, use that */
+ prop = fdt_getprop(fit, sig_offset, "sign-images", &len);
+ if (!prop) {
+ prop = default_list;
+ len = sizeof(default_list);
+ }
+
+ /* Locate the images */
+ end = prop + len;
+ for (iname = prop; iname < end; iname += strlen(iname) + 1) {
+ image_noffset = fit_conf_get_prop_node(fit, conf_noffset,
+ iname);
+ if (image_noffset < 0)
+ return -ENOENT;
+
+ ret = fit_image_verify_arbvn(fit, image_noffset);
+ if (ret)
+ return ret;
+ }
+
+ return 0;
+}
+#endif
+
static int fit_config_verify_sig(const void *fit, int conf_noffset,
const void *sig_blob, int sig_offset)
{
@@ -401,6 +472,14 @@ static int fit_config_verify_sig(const void *fit, int conf_noffset,
goto error;
}

+#if !defined(USE_HOSTCC)
+ if (IMAGE_ENABLE_ARBP && verified) {
+ ret = fit_config_verify_arbvn(fit, conf_noffset, noffset);
+ if (ret)
+ verified = 0;
+ }
+#endif
+
if (verified)
return 0;

diff --git a/common/image-fit.c b/common/image-fit.c
index d54eff9033..97029853b9 100644
--- a/common/image-fit.c
+++ b/common/image-fit.c
@@ -1025,6 +1025,30 @@ int fit_image_get_data_and_size(const void *fit, int noffset,
return ret;
}

+/**
+ * Get 'arbvn' property from a given image node.
+ *
+ * @fit: pointer to the FIT image header
+ * @noffset: component image node offset
+ * @arbvn: holds the arbvn property value
+ *
+ * returns:
+ * 0, on success
+ * -ENOENT if the property could not be found
+ */
+int fit_image_get_arbvn(const void *fit, int noffset, uint32_t *arbvn)
+{
+ const fdt32_t *val;
+
+ val = fdt_getprop(fit, noffset, FIT_ARBVN_PROP, NULL);
+ if (!val)
+ return -ENOENT;
+
+ *arbvn = fdt32_to_cpu(*val);
+
+ return 0;
+}
+
/**
* fit_image_hash_get_algo - get hash algorithm name
* @fit: pointer to the FIT format image header
diff --git a/include/image.h b/include/image.h
index 9a5a87dbf8..72a963cf27 100644
--- a/include/image.h
+++ b/include/image.h
@@ -1005,6 +1005,7 @@ int booti_setup(ulong image, ulong *relocated_addr, ulong *size,
#define FIT_COMP_PROP "compression"
#define FIT_ENTRY_PROP "entry"
#define FIT_LOAD_PROP "load"
+#define FIT_ARBVN_PROP "arbvn"

/* configuration node */
#define FIT_KERNEL_PROP "kernel"
@@ -1085,6 +1086,7 @@ int fit_image_get_data_size_unciphered(const void *fit, int noffset,
size_t *data_size);
int fit_image_get_data_and_size(const void *fit, int noffset,
const void **data, size_t *size);
+int fit_image_get_arbvn(const void *fit, int noffset, uint32_t *arbvn);

int fit_image_hash_get_algo(const void *fit, int noffset, char **algo);
int fit_image_hash_get_value(const void *fit, int noffset, uint8_t **value,
@@ -1186,6 +1188,7 @@ int calculate_hash(const void *data, int data_len, const char *algo,
* device
*/
#if defined(USE_HOSTCC)
+# define IMAGE_ENABLE_ARBP 0
# if defined(CONFIG_FIT_SIGNATURE)
# define IMAGE_ENABLE_SIGN 1
# define IMAGE_ENABLE_VERIFY 1
@@ -1200,6 +1203,7 @@ int calculate_hash(const void *data, int data_len, const char *algo,
# define IMAGE_ENABLE_SIGN 0
# define IMAGE_ENABLE_VERIFY CONFIG_IS_ENABLED(RSA_VERIFY)
# define FIT_IMAGE_ENABLE_VERIFY CONFIG_IS_ENABLED(FIT_SIGNATURE)
+# define IMAGE_ENABLE_ARBP CONFIG_IS_ENABLED(FIT_ARBP)
#endif

#if IMAGE_ENABLE_FIT
@@ -1544,6 +1548,25 @@ int board_fit_config_name_match(const char *name);
void board_fit_image_post_process(void **p_image, size_t *p_size);
#endif /* CONFIG_SPL_FIT_IMAGE_POST_PROCESS */

+#if defined(CONFIG_FIT_ARBP)
+/**
+ * board_get_arbvn() - get the arbvn stored in the platform secure storage.
+ *
+ * @ih_type: image type
+ * @arbvn: pointer to the arbvn
+ * @return 0 if upon successful retrieval, non-zero upon failure.
+ */
+int board_get_arbvn(uint8_t ih_type, uint32_t *arbvn);
+/**
+ * board_set_arbvn() - set the arbvn stored in the platform secure storage.
+ *
+ * @ih_type: image type
+ * @arbvn: new arbvn value to store in the platform secure storage.
+ * @return 0 if stored successfully, non-zero upon failure.
+ */
+int board_set_arbvn(uint8_t ih_type, uint32_t arbvn);
+#endif /* CONFIG_FIT_ARBP */
+
#define FDT_ERROR ((ulong)(-1))

ulong fdt_getprop_u32(const void *fdt, int node, const char *prop);
--
2.25.2