Hello all,

First time i propose a patch to OP-TEE and i do not know the process.

I try this channel.

I filled a ticket on github with all the info:

https://github.com/OP-TEE/optee_os/issues/1168

Best regards

Manu

Hello all,

It seems there is an issue in the TEE adaptation of the libtomcrypt for clearing big numbers.

Issue could be seen in the sequence:

TEE_AllocateTransientObject

TEE_ResetTransientObject

TEE_PopulateTransientObject

where TEE_ResetTransientObject clears (and not free) the object. Clear mean zero the data. If this object is a big number, the leaf function is:

static void bn_clear(struct bignum *s)

{

        struct mpa_numbase_struct *bn = (struct mpa_numbase_struct *)s;

        memset(bn, 0, bn->alloc);

}

corresponding to

static struct bignum *bn_allocate(size_t size_bits)

{

..

bn->alloc = sz - MPA_NUMBASE_METADATA_SIZE_IN_U32 * sizeof(uint32_t);

..

}

The underlying structure describing struct bignum is in lib/libmpa/include/mpalib.h:

typedef struct mpa_numbase_struct {

         mpa_asize_t alloc;

         mpa_usize_t size;

         mpa_word_t d[];

} mpa_num_base;

As we can see, memset fills with zero not only the data, but the metadata and the begin of the datas, instead of zero only the whole data.

Based on OP-TEE 2.2.0, even with the last commit 36d5a31, a proposed patch:

diff --git a/core/lib/libtomcrypt/src/tee_ltc_provider.c b/core/lib/libtomcrypt/src/tee_ltc_provider.c

index fda9454..69620c6 100644

--- a/core/lib/libtomcrypt/src/tee_ltc_provider.c

+++ b/core/lib/libtomcrypt/src/tee_ltc_provider.c

@@ -691,7 +691,7 @@ static void bn_clear(struct bignum *s)

{

        struct mpa_numbase_struct *bn = (struct mpa_numbase_struct *)s;

-       memset(bn, 0, bn->alloc);

+       memset(bn->d, 0, bn->alloc);

}

Note:
mpa_numbase_struct.size is never set in this case, but it is not part of this ticket.

Best regards
Manu