Attention is currently required from: Furquan Shaikh, Aaron Durbin.
Julius Werner would like Furquan Shaikh and Aaron Durbin to review this change.
cbfs: Add file data hashing for CONFIG_CBFS_VERIFICATION
This patch adds file data hashing for CONFIG_CBFS_VERIFICATION. With
this, all CBFS accesses using the new CBFS APIs (cbfs_load/_map/_alloc
and variants) will be fully verified when verification is enabled. (Note
that some use of legacy APIs remains and thus the CBFS_VERIFICATION
feature is not fully finished.)
Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: Ic9fff279f69cf3b7c38a0dc2ff3c970eaa756aa8
---
M src/commonlib/bsd/cbfs_private.c
M src/commonlib/bsd/include/commonlib/bsd/cbfs_mdata.h
M src/lib/cbfs.c
3 files changed, 74 insertions(+), 13 deletions(-)
git pull ssh://review.coreboot.org:29418/coreboot refs/changes/84/52084/1
diff --git a/src/commonlib/bsd/cbfs_private.c b/src/commonlib/bsd/cbfs_private.c
index 91f81e0..16bab7c 100644
--- a/src/commonlib/bsd/cbfs_private.c
+++ b/src/commonlib/bsd/cbfs_private.c
@@ -190,3 +190,26 @@
return NULL;
}
+
+const struct vb2_hash *cbfs_file_hash(const union cbfs_mdata *mdata)
+{
+ /* Hashes are variable-length attributes, so need to manually check the length. */
+ const struct cbfs_file_attr_hash *attr =
+ cbfs_find_attr(mdata, CBFS_FILE_ATTR_TAG_HASH, 0);
+ if (!attr)
+ return NULL; /* no hash */
+ const size_t asize = be32toh(attr->len);
+
+ const struct vb2_hash *hash = &attr->hash;
+ const size_t hsize = vb2_digest_size(hash->algo);
+ if (!hsize) {
+ ERROR("Hash algo %u for '%s' unsupported.\n", hash->algo, mdata->h.filename);
+ return NULL;
+ }
+ if (hsize != asize - offsetof(struct cbfs_file_attr_hash, hash.raw)) {
+ ERROR("Hash attribute size for '%s' (%zu) incorrect for algo %u.\n",
+ mdata->h.filename, asize, hash->algo);
+ return NULL;
+ }
+ return hash;
+}
diff --git a/src/commonlib/bsd/include/commonlib/bsd/cbfs_mdata.h b/src/commonlib/bsd/include/commonlib/bsd/cbfs_mdata.h
index df13427..ed5c378 100644
--- a/src/commonlib/bsd/include/commonlib/bsd/cbfs_mdata.h
+++ b/src/commonlib/bsd/include/commonlib/bsd/cbfs_mdata.h
@@ -24,4 +24,7 @@
else caller is responsible for checking the |len| field to avoid reading out-of-bounds. */
const void *cbfs_find_attr(const union cbfs_mdata *mdata, uint32_t attr_tag, size_t size_check);
+/* Returns pointer to CBFS file hash structure in metadata attributes, or NULL if invalid. */
+const struct vb2_hash *cbfs_file_hash(const union cbfs_mdata *mdata);
+
#endif /* _COMMONLIB_BSD_CBFS_MDATA_H_ */
diff --git a/src/lib/cbfs.c b/src/lib/cbfs.c
index 9135b2f..23e8f41 100644
--- a/src/lib/cbfs.c
+++ b/src/lib/cbfs.c
@@ -186,11 +186,27 @@
return true;
}
-static size_t cbfs_load_and_decompress(const struct region_device *rdev,
- void *buffer, size_t buffer_size, uint32_t compression)
+static inline bool cbfs_file_hash_mismatch(const void *buffer, size_t size,
+ const struct vb2_hash *file_hash)
+{
+ /* Avoid linking hash functions when verification is disabled. */
+ if (!CONFIG(CBFS_VERIFICATION))
+ return false;
+
+ /* If there is no file hash, always count that as a mismatch. */
+ if (file_hash && vb2_hash_verify(buffer, size, file_hash) == VB2_SUCCESS)
+ return false;
+
+ printk(BIOS_CRIT, "CBFS file hash mismatch!\n");
+ return true;
+}
+
+static size_t cbfs_load_and_decompress(const struct region_device *rdev, void *buffer,
+ size_t buffer_size, uint32_t compression,
+ const struct vb2_hash *file_hash)
{
size_t in_size = region_device_sz(rdev);
- size_t out_size;
+ size_t out_size = 0;
void *map;
DEBUG("Decompressing %zu bytes to %p with algo %d\n", in_size, buffer, compression);
@@ -201,6 +217,8 @@
return 0;
if (rdev_readat(rdev, buffer, 0, in_size) != in_size)
return 0;
+ if (cbfs_file_hash_mismatch(buffer, in_size, file_hash))
+ return 0;
return in_size;
case CBFS_COMPRESS_LZ4:
@@ -213,9 +231,11 @@
if (map == NULL)
return 0;
- timestamp_add_now(TS_START_ULZ4F);
- out_size = ulz4fn(map, in_size, buffer, buffer_size);
- timestamp_add_now(TS_END_ULZ4F);
+ if (!cbfs_file_hash_mismatch(map, in_size, file_hash)) {
+ timestamp_add_now(TS_START_ULZ4F);
+ out_size = ulz4fn(map, in_size, buffer, buffer_size);
+ timestamp_add_now(TS_END_ULZ4F);
+ }
rdev_munmap(rdev, map);
@@ -228,10 +248,12 @@
if (map == NULL)
return 0;
- /* Note: timestamp not useful for memory-mapped media (x86) */
- timestamp_add_now(TS_START_ULZMA);
- out_size = ulzman(map, in_size, buffer, buffer_size);
- timestamp_add_now(TS_END_ULZMA);
+ if (!cbfs_file_hash_mismatch(map, in_size, file_hash)) {
+ /* Note: timestamp not useful for memory-mapped media (x86) */
+ timestamp_add_now(TS_START_ULZMA);
+ out_size = ulzman(map, in_size, buffer, buffer_size);
+ timestamp_add_now(TS_END_ULZMA);
+ }
rdev_munmap(rdev, map);
@@ -318,11 +340,18 @@
if (size_out)
*size_out = size;
+ const struct vb2_hash *file_hash = NULL;
+ if (CONFIG(CBFS_VERIFICATION))
+ file_hash = cbfs_file_hash(&mdata);
+
/* allocator == NULL means do a cbfs_map() */
if (allocator) {
loc = allocator(arg, size, &mdata);
} else if (compression == CBFS_COMPRESS_NONE) {
- return rdev_mmap_full(&rdev);
+ void *mapping = rdev_mmap_full(&rdev);
+ if (!mapping || cbfs_file_hash_mismatch(mapping, size, file_hash))
+ return NULL;
+ return mapping;
} else if (!CBFS_CACHE_AVAILABLE) {
ERROR("Cannot map compressed file %s on x86\n", mdata.h.filename);
return NULL;
@@ -335,7 +364,7 @@
return NULL;
}
- size = cbfs_load_and_decompress(&rdev, loc, size, compression);
+ size = cbfs_load_and_decompress(&rdev, loc, size, compression, file_hash);
if (!size)
return NULL;
@@ -384,12 +413,18 @@
prog_set_entry(pstage, prog_start(pstage) +
be32toh(sattr->entry_offset), NULL);
+ const struct vb2_hash *file_hash = NULL;
+ if (CONFIG(CBFS_VERIFICATION))
+ file_hash = cbfs_file_hash(&mdata);
+
/* Hacky way to not load programs over read only media. The stages
* that would hit this path initialize themselves. */
if ((ENV_BOOTBLOCK || ENV_SEPARATE_VERSTAGE) &&
!CONFIG(NO_XIP_EARLY_STAGES) && CONFIG(BOOT_DEVICE_MEMORY_MAPPED)) {
void *mapping = rdev_mmap_full(&rdev);
rdev_munmap(&rdev, mapping);
+ if (cbfs_file_hash_mismatch(mapping, region_device_sz(&rdev), file_hash))
+ return CB_CBFS_HASH_MISMATCH;
if (mapping == prog_start(pstage))
return CB_SUCCESS;
}
@@ -405,7 +440,7 @@
}
size_t fsize = cbfs_load_and_decompress(&rdev, prog_start(pstage), prog_size(pstage),
- compression);
+ compression, file_hash);
if (!fsize)
return CB_ERR;
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