Pointer alignment in TriCore architecture

[edzardsh]

Version

5.9.0

Description

During testing, we encountered a trap when wc_InitRng() was called. The trap was triggered by a write to one of the RNG structure fields:
rng->drbg = NULL;

The code runs on Infineon TriCore TC29 and TC26 devices, whose architecture only supports word-aligned pointers.
See https://resources.tasking.com/sites/default/files/2021-02/TASKING_Alignment%20Requirements%20Restrictions_WEB.pdf

We examined the memory and saw that the drbg field was not word-aligned.
We fixed this by adding the __align(4) directive to the WC_RNG struct definition to enforce word alignment. The structure now looks as follows:

/* RNG context */
struct WC_RNG {
    struct OS_Seed seed;
    void* heap;
    byte status;
 
#if defined(WC_RNG_BANK_SUPPORT) || defined(HAVE_HASHDRBG)
 
#ifdef HAVE_ANONYMOUS_INLINE_AGGREGATES
    union {
#endif
 
    #ifdef WC_RNG_BANK_SUPPORT
        struct wc_rng_bank *bankref;
    #endif
 
    #ifdef HAVE_HASHDRBG
        #ifdef HAVE_ANONYMOUS_INLINE_AGGREGATES
        struct {
        #endif
            /* Hash-based Deterministic Random Bit Generator */
           struct DRBG* drbg;
        #if defined(WOLFSSL_NO_MALLOC) && !defined(WOLFSSL_STATIC_MEMORY)
            struct DRBG_internal drbg_data;
        #endif
        #ifdef WOLFSSL_SMALL_STACK_CACHE
            /* Scratch buffers -- all preallocated by _InitRng(). */
            struct DRBG_internal *drbg_scratch;
            byte *health_check_scratch;
            byte *newSeed_buf;
        #endif
        #ifdef HAVE_ANONYMOUS_INLINE_AGGREGATES
        };
        #endif
    #endif /* HAVE_HASHDRBG */
 
#ifdef HAVE_ANONYMOUS_INLINE_AGGREGATES
    };
#endif
 
#endif /* WC_RNG_BANK_SUPPORT || HAVE_HASHDRBG */
 
#if defined(HAVE_GETPID) && !defined(WOLFSSL_NO_GETPID)
    pid_t pid;
#endif
#ifdef WOLFSSL_ASYNC_CRYPT
    WC_ASYNC_DEV asyncDev;
#endif
#if defined(WOLFSSL_ASYNC_CRYPT) || defined(WOLF_CRYPTO_CB)
    int devId;
#endif
} __align(4);

We are not sure if this was caused by our user settings or if this could potentially affect other structs or memory accesses.

Our user_settings.h looks like this:

//Platform/Porting
//======================================================
/* Define a macro to display user settings version in example code: */
#define WOLFSSL_USER_SETTINGS_ID "TriCore TC29 user_settings.h"
 
#define NO_FILESYSTEM
#define SINGLE_THREADED
/* disable the built-in socket support and use the IO callbacks */
#define WOLFSSL_NO_SOCK
/* user recv/send callbacks for network IO */
#define WOLFSSL_USER_IO
#define NO_WRITEV
#define WOLFSSL_IGNORE_FILE_WARN
 
/* Time porting */
#define TIME_OVERRIDES
#define HAVE_TIME_T_TYPE
extern volatile unsigned long jiffies;
static inline long XTIME(long *x) { return jiffies;}
#define WOLFSSL_USER_CURRTIME
#define NO_ASN_TIME
/* Allow user supplied ptr type */
#define WC_PTR_TYPE
 
/*-- strcasecmp */
#define XSTRCASECMP(s1,s2) strcmp((s1),(s2))
 
#define WOLFSSL_NO_ATOMIC
#define WOLFSSL_GENSEED_FORTEST
//#define CUSTOM_RAND_GENERATE_SEED(output, sz) (rand_gen_seed)
/* wolfSSL comes bundled with test certificate and key files */
/*These buffers are available in certs_test.h when defining one or more of USE_CERT_BUFFERS_1024, USE_CERT_BUFFERS_2048, or USE_CERT_BUFFERS_256*/
//#define USE_CERT_BUFFERS_2048
 
/* USE_FAST_MATH is default */
#define USE_FAST_MATH
/*The ALT_ECC_SIZE option can only be enabled with USE_FAST_MATH.*/
//#define ALT_ECC_SIZE
 
 
//Memory Usage
//======================================================
//#define WOLFSSL_STATIC_MEMORY
//#define WOLFSSL_STATIC_MEMORY_LEAN
//#define WOLFSSL_NO_MALLOC
/* Cannot use WOLFSSL_NO_MALLOC with small stack? */
#define WOLFSSL_SMALL_STACK
//#define WOLFSSL_SMALL_STACK_EXTRA
//#define WOLFSSL_SMALL_STACK_CIPHERS
//#define MICRO_SESSION_CACHE
#define NO_SESSION_CACHE
#define WOLFSSL_LOW_MEMORY
 
#ifdef WOLFSSL_NO_MALLOC
#define WOLFSSL_DYN_CERT
#endif
 
 
//TLS Settings
//======================================================
#define NO_TLS
#define NO_WOLFSSL_SERVER
#define NO_WOLFSSL_CLIENT
#define NO_OLD_TLS
#undef HAVE_TLS_EXTENSIONS
#undef HAVE_SUPPORTED_CURVES
/* TLS 1.3                                 */
#define WOLFSSL_TLS13
#if defined ( WOLFSSL_TLS13 )
    #define HAVE_TLS_EXTENSIONS
    #define WC_RSA_PSS
    #define HAVE_AEAD
#endif
  #define HAVE_HKDF
 
//Algorithms/Features
//======================================================
 
//#undef WOLFSSL_ASN_TEMPLATE
 
/* Enable PRNG (SHA2-256) */
#define HAVE_HASHDRBG
 
#define HAVE_AESGCM
#define HAVE_ECC
#define HAVE_ECC_ENCRYPT
 
 
/* Reduce memory usage */
//#define USE_SLOW_SHA256
 
#define WOLFSSL_BASE64_ENCODE
 
/*Disable unused algorithms/features */
//#define NO_RSA
#define WC_NO_RSA_OAEP
#define NO_DH
#define NO_DSA
#define NO_RC4
#define NO_MD5
#define NO_SHA
#define NO_PSK
#define NO_HC128
#define NO_RABBIT
#define NO_MD4
#define NO_DES3
#define NO_PWDBASED
#define NO_AES_256
#define NO_AES_192
#define NO_ASN_TIME
#define NO_MULTIBYTE_PRINT
#define NO_OLD_WC_NAMES
#define NO_OLD_POLY1305
 
 
#define WOLFSSL_NOSHA512_224
#define WOLFSSL_NOSHA512_256

Should there be an option for every struct to specify alignment and/or other packing methods?

[kareem-wolfssl]

Hi @edzardsh,

We do currently provide the flag WOLFSSL_USE_ALIGN, but this isn't currently aligning any structs. I'm reviewing this with the team to determine the best approach on this.

[kareem-wolfssl]

Hi @edzardsh,

How are you allocating the WC_RNG struct before calling wc_InitRng? Does your platform's malloc return aligned pointers?

[kareem-wolfssl]

Hi @edzardsh,

After reviewing this with the team, we believe this is a compiler bug. Please share which compiler you are using and your build settings (ie. CFLAGS etc). Have you contacted your compiler's company about this issue?

[koehlkec]

Hi,

we will contact our compiler company Tasking.
This application note states that pointers must always be word aligned.
https://resources.tasking.com/sites/default/files/2021-02/TASKING_Alignment%20Requirements%20Restrictions_WEB.pdf

ALIGNMENT RESTRICTIONS OF THE TRICORE ARCHITECTURE
Pointers must always be word aligned.
The TASKING C compiler for TriCore ensures that those alignment restrictions are not violated.

the compiler we are using is:

.\ctc.exe --version
TASKING VX-toolset for TriCore: C compiler   v6.3r1 Build 19041558

i have looked trough the the Compiler Flags and found:

--align=0 

By default (value 0) the C compiler aligns variables and functions to the minimum alignment required by the architecture.

That doesn't seem to work properly.