Re: [mbed-tls] How to setup config.h to make memory_buffer_alloc_init() thread-safe?

-- Gilles Peskine Mbed TLS developer On 29/07/2021 22:38, Shariful Alam wrote: > Hi Gilles, > Hope you are well. The project that I'm currently working on requires > static memory allocation instead of dynamic memory allocation. I was > trying to use  "memory_buffer_alloc()". Since memory_buffer_alloc() > doesn't support multiple memory pools, seems like I can't use this > function in my project.  > > I have a working version of a modified bignum.c & bignum.h, where > malloc is replaced with an array. The library is working. However, the > performance is poor (~4 times slower). I was wondering what could > cause this slow performance. I mean, I understand it will be slow, but > I did not expect it to be 4 times slower.  > > Is there any version, where an array was used instead of malloc? Or if > you could point out some of the reasons for this library to slow down > while using an array, I will be very grateful. > > Best regards, > Shariful >     > > On Tue, Jul 20, 2021 at 2:22 PM Gilles Peskine <gilles.peskine@arm.com > mailto:gilles.peskine@arm.com> wrote: > > Hi Shariful, > > You just call mbedtls_calloc() (or let other functions call it). > It will use the memory pool set by mbedtls_memory_buffer_alloc_init(). > > The memory_buffer_alloc module does not support multiple memory > pools. If you want a separate pool for each thread's allocation > for performance reasons on a multicore system, you'd better rely > on your platform's built-in calloc(). It's likely to be > fined-tuned for multicore operation. The built-in allocator in > Mbed TLS is intended for highly resource-constrained systems where > the basic platform doesn't even include an allocator. > > Best regards, > > -- > Gilles Peskine > Mbed TLS developer > > On 20/07/2021 22:10, Shariful Alam wrote: >> Hi Gilles, >> Thank you very much, for your reply. Sorry to bother you again. I >> am trying to follow your instructions. I have a question >> regarding your suggestions. >> >> You said "applications call mbedtls_memory_buffer_alloc_init() in >> the startup code of the initial thread, before creating other >> threads. The alloc/free functions are thread-safe, but the >> initialization and deinitialization functions aren't."  >> >> I'm a little confused here. Say, if I call >> mbedtls_memory_buffer_alloc_init() with a buffer in the main >> thread, how did all other threads use this memory (or how do all >> the threads know which memory block to use)? >> >> After calling mbedtls_memory_buffer_alloc_init() in the main >> thread, I can get the address of the buffer and pass it to the >> threads, do I have to call mbedtls_memory_buffer_alloc_init() >> again inside each thread?    >> >> Thanks, >> Shariful >> >> On Mon, Jul 19, 2021 at 3:48 AM Gilles Peskine via mbed-tls >> <mbed-tls@lists.trustedfirmware.org >> mailto:mbed-tls@lists.trustedfirmware.org> wrote: >> >> Hi Shariful, >> >> First, please note that the library called PolarSSL with >> functions like >> rsa_private() and memory_buffer_alloc_init() has not been >> supported for >> several years. You should upgrade to Mbed TLS, with functions >> like >> mbedtls_rsa_private() and mbedtls_memory_buffer_alloc_init(). >> That being >> said, the memory_buffer_alloc module works in the same way. >> >> Normally, applications call >> mbedtls_memory_buffer_alloc_init() in the >> startup code of the initial thread, before creating other >> threads. The >> alloc/free functions are thread-safe, but the initialization and >> deinitialization functions aren't. If you must call >> mbedtls_memory_buffer_alloc_init() after creating other >> threads, make >> sure that no thread calls mbedtls_calloc until >> mbedtls_memory_buffer_alloc_init() has returned. >> >> The same principle applies to other parts of Mbed TLS that are >> thread-safe. For example, only the RSA operations (encryption, >> decryption, signature, verification, and also the low-level >> functions >> mbedtls_rsa_public() and mbedtls_rsa_private()) are >> protected. So you >> must finish setting up the RSA key inside one thread before >> you pass a >> pointer to other threads. Similarly, only >> mbedtls_xxx_drbg_random() is >> thread-safe, and the RNG setup (including >> mbedtls_xxx_drgb_seed()) >> should be done as part of the initial application startup. >> >> Finally, note that mbedtls_rsa_private() alone cannot decrypt >> a message: >> all it does it to apply the private key operation. To decrypt >> a simple >> message encrypted with RSA-OAEP, call >> mbedtls_rsa_rsaes_oaep_decrypt() >> or mbedtls_rsa_pkcs1_decrypt() with a key set up for >> MBEDTLS_RSA_PKCS_V21 encoding. To use the legacy PKCS#1v1.5 >> mechanism, >> call mbedtls_rsa_rsaes_pkcs1_v15_decrypt() or >> mbedtls_rsa_pkcs1_decrypt() with a key set up for >> .MBEDTLS_RSA_PKCS_V15. >> To decrypt a message using a RSA FDH hybrid scheme, you do >> need to call >> mbedtls_rsa_private() since Mbed TLS doesn't support it >> natively, but >> what this gives you is the intermediate secret from which you >> then need >> to derive a symmetric key, not the message itself. >> >> Best regards, >> >> -- >> Gilles Peskine >> Mbed TLS developer >> >> On 18/07/2021 07:16, Shariful Alam via mbed-tls wrote: >> > Hello, >> > I have a simple example code to decrypt an >> encrypted message using >> > *rsa_private()*. I use *memory_buffer_alloc_init(),  *in >> order to use >> > a static memory for the computation. I want to run my code >> > concurrently. My code works with a single pthread. However, >> when I try >> > to run more than one thread my program fails to decrypt.  >> > >> > ** I check the same code >> without *memory_buffer_alloc_init(), *it >> > works concurrently, without any issues at all.  >> > >> > Therefore, I believe, the issue that I'm facing is >> coming from the use >> > of static memory(e.g. *memory_buffer_alloc_init()*). The >> documentation >> > of memorry_buffer_alloc.h shows, >> > >> >     /**  >> > >> >     * \brief   Initialize use of stack-based memory allocator.  >> > >> >     *           The stack-based allocator does memory >> management >> >     inside the  >> > >> >     *          presented buffer and does not call malloc() >> and free().  >> > >> >     *          It sets the global polarssl_malloc() and >> >     polarssl_free() pointers  >> > >> >     *          to its own functions.  >> > >> >     *          (Provided polarssl_malloc() and >> polarssl_free() are >> >     thread-safe if  >> > >> >     *           POLARSSL_THREADING_C is defined) >> > >> >     *  >> > >> >     * \note    This code is not optimized and provides a >> straight-forward  >> > >> >     *          implementation of a stack-based memory >> allocator.  >> > >> >     *  >> > >> >     * \param buf   buffer to use as heap  >> > >> >     * \param len   size of the buffer  >> > >> >     *  >> > >> >     * \return              0 if successful  >> > >> >     */    >> > >> > >> > So, I added the following configuration to the *config.h* >> file   >> > >> >     1. #define POLARSSL_THREADING_PTHREAD >> >     2. #define POLARSSL_THREADING_C >> > >> > But I'm still getting errors while decrypting. Any help on >> how to fix >> > this? or what else should I add into the config.h file to >> > make *memory_buffer_alloc_init() *thread-safe? Here is my >> sample >> > code: https://pastebin.com/uyW3vknt >> https://pastebin.com/uyW3vknt >> <https://pastebin.com/uyW3vknt https://pastebin.com/uyW3vknt> >> > >> > Thanks, >> > Shariful >> > >> >> -- >> mbed-tls mailing list >> mbed-tls@lists.trustedfirmware.org >> mailto:mbed-tls@lists.trustedfirmware.org >> https://lists.trustedfirmware.org/mailman/listinfo/mbed-tls >> https://lists.trustedfirmware.org/mailman/listinfo/mbed-tls >> >