Loading a TA, which is an ELF binary, triggers a lot of operations done on the content of the ELF structure/info which are under REE control. It would be preferable to fully authenticate the binary before doing any of those ELF related operations (loading segments etc). This will not prevent the ELF manipulation from going wrong, but it will move the threat from anyone on the REE accessing the binaries, to restricted people having a valid key to sign a binary.

e.g. for REE FS TA storage, the hash is verified only when full binary have been consumed, which is at the end of the ELF binding process. See ree_fs_ta.c::ta_read().

Additionally, this is a weak spot: a lot of operations rely on getting there, if the check_digest() never happens for X reason, the caller will just keep going (effectively allowing a non-authenticated TA to run). No attack path where identified, but some may exist or may be introduced to alter either the handle->nw_ta_size in ree_fs_ta.c, or the state->data_len in elf_load.c allowing to bypass the digest check.

Patches

optee_os.git

• core: REE FS TAs: add option to verify signature before processing (7db24ad)

Workarounds

N/A

References

N/A

OP-TEE ID

OP-TEE-2019-0005

Reported by

Netflix (Bastien Simondi)

For more information

For more information regarding the security incident process in OP-TEE, please read the information that can be found when going to the "Security" page at https://www.trustedfirmware.org.