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From df6bfa8d2d429addea3dfd9d1bfb3933b4adb7e7 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 | 19 +++++++++++++
include/libfdt.h | 1 +
lib/libfdt/fdt_ro.c | 65 +++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 104 insertions(+)
diff --git a/Kconfig b/Kconfig
index d6439d01ca60..1c1267fee079 100644
--- a/Kconfig
+++ b/Kconfig
@@ -222,11 +222,21 @@ config FIT_VERBOSE
bool "Display verbose messages on FIT boot"
depends on FIT
+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 FIT
depends on DM
select RSA
+ select FIT_FULL_CHECK
help
This option enables signature verification of FIT uImages,
using a hash signed and verified using RSA. If
@@ -240,11 +250,20 @@ config FIT_SIGNATURE
format support in this case, enable it using
CONFIG_IMAGE_FORMAT_LEGACY.
+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_FIT
depends on SPL_DM
select SPL_RSA
+ select SPL_FIT_FULL_CHECK
config FIT_BEST_MATCH
bool "Select the best match for the kernel device tree"
diff --git a/common/image-fit.c b/common/image-fit.c
index 34bbc8645205..78db32e89f6f 100644
--- a/common/image-fit.c
+++ b/common/image-fit.c
@@ -24,11 +24,14 @@ DECLARE_GLOBAL_DATA_PTR;
#endif /* !USE_HOSTCC*/
#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>
+#define log_debug(fmt, args...) debug(fmt, ##args)
+
/*****************************************************************************/
/* New uImage format routines */
/*****************************************************************************/
@@ -1239,6 +1242,22 @@ int fit_check_format(const void *fit, ulong size)
}
}
+ 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) {
log_debug("Wrong FIT format: no images parent node\n");
diff --git a/include/libfdt.h b/include/libfdt.h
index 74b1d149c2dd..6a4b2f871205 100644
--- a/include/libfdt.h
+++ b/include/libfdt.h
@@ -1980,4 +1980,5 @@ 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 /* _LIBFDT_H */
diff --git a/lib/libfdt/fdt_ro.c b/lib/libfdt/fdt_ro.c
index 12214c2dc2b5..5ae4b84d6e54 100644
--- a/lib/libfdt/fdt_ro.c
+++ b/lib/libfdt/fdt_ro.c
@@ -625,3 +625,68 @@ 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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