MicroBlaze does not return from mbedtls_pk_parse_key with MBEDTLS_HAVE_ASM defined

[IsaacJT]

Description

• Type: Bug
• Priority: Major

---

Bug

OS
FreeRTOS

mbed TLS build:
Version: 2.12.0
OS version: 10.0
Configuration:
mbedtls_freertos.txt
Compiler and options (if you used a pre-built binary, please indicate how you obtained it): GCC 7.2.0 from Xilinx SDK 2018.1. Compiled with: -O2 -mcpu=v10.0 -mxl-multiply-high -mno-xl-soft-div -mno-xl-soft-mul -mxl-barrel-shift -mxl-pattern-compare
Additional environment information: we are also using Mongoose web server. The MicroBlaze has been built with multiplier and divider hardware, branch prediction, and data and instruction caches.

Expected behavior
When parsing a buffer with mbedtls_pk_parse_key, the function should return.

Actual behavior
The mbedtls_pk_parse_key never returns, and is stuck performing the multiplication in bignum.c.

The function executes and returns correctly when compiling without MBEDTLS_HAVE_ASM defined.

Steps to reproduce
Attempt to parse a key with mbedtls_pk_parse_key on a MicroBlaze with MBEDTLS_HAVE_ASM defined.

[IsaacJT]

The application gets stuck in the do while loop here: https://github.com/ARMmbed/mbedtls/blob/6c34268e203d23bbfbfda3f7362dac8b9b9382bc/library/bignum.c#L1407

The mbedtls_mpi_cmp_mpi function always returns 1.

[ciarmcom]

ARM Internal Ref: IOTSSL-2540

[Patater]

Hi @IsaacJT

Thanks for your bug report. We unfortunately don't have a way to reproduce this issue, so I've marked this as open for community contribution.

Thanks!

[Eurecam-Benjamin]

I also runned into this issue when using mbedtls on a microblaze.
I am no microblaze guru but I further analyse the code by comparing it to the default C fallback :

• There is indeed a little/big endian problem when using "lhui" instruction -> I replaced it with "lwi" and masking / shifting value to upper and lower bits
• To me, there are also some typo with r0 register confused with 0 number.
• And last, some registers where swapped.

The attached diff file fixes include/mbedtls/nb_mul.h in branche 2.16
The lines number doesn't match but it works also with 2.28 and almost certainly with the newer 3.1 as they share the code.

fix_bn_mul.txt