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From cf469ab0783da6783f89a8e31c213f19fdf38dba Mon Sep 17 00:00:00 2001
From: Simon Glass <sjg@chromium.org>
Date: Mon, 15 Feb 2021 17:08:10 -0700
Subject: [PATCH] image: Add an option to do a full check of the FIT
Some strange modifications of the FIT can introduce security risks. Add an
option to check it thoroughly, using libfdt's fdt_check_full() function.
Enable this by default if signature verification is enabled.
CVE-2021-27097
Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Bruce Monroe <bruce.monroe@intel.com>
Reported-by: Arie Haenel <arie.haenel@intel.com>
Reported-by: Julien Lenoir <julien.lenoir@intel.com>
---
Kconfig | 19 ++++++++++++
common/image-fit.c | 20 ++++++++++++-
include/linux/libfdt.h | 2 ++
lib/libfdt/fdt_ro.c | 65 ++++++++++++++++++++++++++++++++++++++++++
4 files changed, 105 insertions(+), 1 deletion(-)
diff --git a/Kconfig b/Kconfig
index b62bcdbccf1e..0165ca33c5d1 100644
--- a/Kconfig
+++ b/Kconfig
@@ -318,11 +318,21 @@ config FIT_ENABLE_SHA512_SUPPORT
SHA512 checksum is a 512-bit (64-byte) hash value used to check that
the image contents have not been corrupted.
+config FIT_FULL_CHECK
+ bool "Do a full check of the FIT before using it"
+ default y
+ help
+ Enable this do a full check of the FIT to make sure it is valid. This
+ helps to protect against carefully crafted FITs which take advantage
+ of bugs or omissions in the code. This includes a bad structure,
+ multiple root nodes and the like.
+
config FIT_SIGNATURE
bool "Enable signature verification of FIT uImages"
depends on DM
select HASH
select RSA
+ select FIT_FULL_CHECK
help
This option enables signature verification of FIT uImages,
using a hash signed and verified using RSA. If
@@ -398,6 +408,14 @@ config SPL_FIT_PRINT
help
Support printing the content of the fitImage in a verbose manner in SPL.
+config SPL_FIT_FULL_CHECK
+ bool "Do a full check of the FIT before using it"
+ help
+ Enable this do a full check of the FIT to make sure it is valid. This
+ helps to protect against carefully crafted FITs which take advantage
+ of bugs or omissions in the code. This includes a bad structure,
+ multiple root nodes and the like.
+
config SPL_FIT_SIGNATURE
bool "Enable signature verification of FIT firmware within SPL"
depends on SPL_DM
@@ -405,6 +423,7 @@ config SPL_FIT_SIGNATURE
select SPL_CRYPTO_SUPPORT
select SPL_HASH_SUPPORT
select SPL_RSA
+ select SPL_FIT_FULL_CHECK
config SPL_LOAD_FIT
bool "Enable SPL loading U-Boot as a FIT"
diff --git a/common/image-fit.c b/common/image-fit.c
index 124d8895cffd..b1926d8b53f8 100644
--- a/common/image-fit.c
+++ b/common/image-fit.c
@@ -15,7 +15,6 @@
#include <time.h>
#else
#include <linux/compiler.h>
-#include <linux/kconfig.h>
#include <common.h>
#include <errno.h>
#include <mapmem.h>
@@ -26,12 +25,15 @@ DECLARE_GLOBAL_DATA_PTR;
#include <image.h>
#include <bootstage.h>
+#include <linux/kconfig.h>
#include <u-boot/crc.h>
#include <u-boot/md5.h>
#include <u-boot/sha1.h>
#include <u-boot/sha256.h>
#include <u-boot/sha512.h>
+#define log_debug(fmt, args...) debug(fmt, ##args)
+
/*****************************************************************************/
/* New uImage format routines */
/*****************************************************************************/
@@ -1487,6 +1489,22 @@ int fit_check_format(const void *fit, ulong size)
return -ENODATA;
}
}
+
+ if (CONFIG_IS_ENABLED(FIT_FULL_CHECK)) {
+ /*
+ * If we are not given the size, make do wtih calculating it.
+ * This is not as secure, so we should consider a flag to
+ * control this.
+ */
+ if (size == IMAGE_SIZE_INVAL)
+ size = fdt_totalsize(fit);
+ ret = fdt_check_full(fit, size);
+
+ if (ret) {
+ log_debug("FIT check error %d\n", ret);
+ return -EINVAL;
+ }
+ }
/* mandatory subimages parent '/images' node */
if (fdt_path_offset(fit, FIT_IMAGES_PATH) < 0) {
diff --git a/include/linux/libfdt.h b/include/linux/libfdt.h
index eeb2344971f3..29c997ada398 100644
--- a/include/linux/libfdt.h
+++ b/include/linux/libfdt.h
@@ -305,6 +305,8 @@ int fdt_next_region(const void *fdt,
*/
int fdt_add_alias_regions(const void *fdt, struct fdt_region *region, int count,
int max_regions, struct fdt_region_state *info);
+
+int fdt_check_full(const void *fdt, size_t bufsize);
#endif /* SWIG */
extern struct fdt_header *working_fdt; /* Pointer to the working fdt */
diff --git a/lib/libfdt/fdt_ro.c b/lib/libfdt/fdt_ro.c
index b6ca4e0b0c30..dfbeb2c21a85 100644
--- a/lib/libfdt/fdt_ro.c
+++ b/lib/libfdt/fdt_ro.c
@@ -680,3 +680,68 @@ int fdt_node_offset_by_compatible(const void *fdt, int startoffset,
return offset; /* error from fdt_next_node() */
}
+
+#define INT_MAX ((int)(~0U>>1))
+
+int fdt_check_full(const void *fdt, size_t bufsize)
+{
+ int err;
+ int num_memrsv;
+ int offset, nextoffset = 0;
+ uint32_t tag;
+ unsigned depth = 0;
+ const void *prop;
+ const char *propname;
+
+ if (bufsize < FDT_V1_SIZE)
+ return -FDT_ERR_TRUNCATED;
+ err = fdt_check_header(fdt);
+ if (err != 0)
+ return err;
+ if (bufsize < fdt_totalsize(fdt))
+ return -FDT_ERR_TRUNCATED;
+
+ num_memrsv = fdt_num_mem_rsv(fdt);
+ if (num_memrsv < 0)
+ return num_memrsv;
+
+ while (1) {
+ offset = nextoffset;
+ tag = fdt_next_tag(fdt, offset, &nextoffset);
+
+ if (nextoffset < 0)
+ return nextoffset;
+
+ switch (tag) {
+ case FDT_NOP:
+ break;
+
+ case FDT_END:
+ if (depth != 0)
+ return -FDT_ERR_BADSTRUCTURE;
+ return 0;
+
+ case FDT_BEGIN_NODE:
+ depth++;
+ if (depth > INT_MAX)
+ return -FDT_ERR_BADSTRUCTURE;
+ break;
+
+ case FDT_END_NODE:
+ if (depth == 0)
+ return -FDT_ERR_BADSTRUCTURE;
+ depth--;
+ break;
+
+ case FDT_PROP:
+ prop = fdt_getprop_by_offset(fdt, offset, &propname,
+ &err);
+ if (!prop)
+ return err;
+ break;
+
+ default:
+ return -FDT_ERR_INTERNAL;
+ }
+ }
+}
--
2.17.1
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