Re: [lwip-users] PolarSSL and mbedTLS

[Noam Weissman]

Hi Jan,

Thanks for responding :-)

When I started this project I found (the hard way) that PolarSSL uses memory 
allocations, and lots of it.
As my system is complicated I cannot spare any of the 192Kb of the micro .

The micro has a second bank that is fast memory (CCM) so I used this one. I 
have allotted all of the CCM 
(64K) for micro heap. The SSL actually needs 2 x 16K + some extras so a minimum 
of about 45-50K... 64 
I think is sufficient ?

I am running a TCP (terminal like telnet) that sends and receives small 
messages. In order not to waste 
memory I have reduced the MSS size to its default and use more buffers. This 
works fine with terminal
HTTP and all... a compromise.

Any way here are my LwIP memory settings:


/* ---------- Memory options ---------- */
/* MEM_ALIGNMENT: should be set to the alignment of the CPU for which
   lwIP is compiled. 4 byte alignment -> define MEM_ALIGNMENT to 4, 2
   byte alignment -> define MEM_ALIGNMENT to 2. */
#define MEM_ALIGNMENT           4

/* MEM_SIZE: the size of the heap memory. If the application will send
   a lot of data that needs to be copied, this should be set high. */
#define MEM_SIZE                (15 * 1024)

/* MEMP_NUM_PBUF: the number of memp struct pbufs.  
  prevoiusly this was high as we understood that the pBuf buffers 
  are allocated from the LwIP heap (MEM_SIZE). But after reducing
  PBUF_POOL_SIZE to 6 the TCP stack started to get slow and hanged.
  
  We found out that the values were wrong and pBuf are allocated 
  from the PBUF_POOL and its size is PBUF_POOL_SIZE * PBUF_POOL_BUFSIZE  
*/
#define MEMP_NUM_PBUF           25

/* MEMP_NUM_UDP_PCB: the number of UDP protocol control blocks. One
   per active UDP "connection". */
#define MEMP_NUM_UDP_PCB        10

/* MEMP_NUM_TCP_PCB: the number of simulatenously active TCP
   connections. */
#define MEMP_NUM_TCP_PCB        20

/* MEMP_NUM_TCP_PCB_LISTEN: the number of listening TCP
   connections. */
#define MEMP_NUM_TCP_PCB_LISTEN 15

/* MEMP_NUM_SYS_TIMEOUT: the number of simulateously active
   timeouts. */
#define MEMP_NUM_SYS_TIMEOUT    15


/* ---------- TCP options ---------- */
#define LWIP_TCP                1
#define TCP_TTL                 255

/* Controls if TCP should queue segments that arrive out of
   order. Define to 0 if your device is low on memory. */
#define TCP_QUEUE_OOSEQ         0

/* TCP Maximum segment size. */
#define TCP_MSS                 536

/* TCP sender buffer space (bytes). */
//
// When TCP_SND_BUF was (4*TCP_MSS) we had problems with memory
// alocation. After reducing it to (3*TCP_MSS) we stopped getting 
// memory allocation errors. After more testing with memory allocation
// I have reduced it to 2 * MSS and now it look OK with no memory alloocation
// problems !!! 
//
#define TCP_SND_BUF             (2 * TCP_MSS)

/*  TCP_SND_QUEUELEN: TCP sender buffer space (pbufs). This must be at least
  as much as (2 * TCP_SND_BUF/TCP_MSS) for things to work. */

#define TCP_SND_QUEUELEN        (6 * (TCP_SND_BUF)/(TCP_MSS))
  
/* TCP receive window. */
#define TCP_WND                 (4 * TCP_MSS)


/* MEMP_NUM_TCP_SEG: the number of simultaneously queued TCP
   segments. */
//#define MEMP_NUM_TCP_SEG        20
#define MEMP_NUM_TCP_SEG        TCP_SND_QUEUELEN // 20  // This was previosly 
20 and cause a MEM_ERR it was changed 
                                                 // to BE THE SAME SIZE AS 
TCP_SND_QUEUELEN

/* ---------- Pbuf options ---------- */
/* PBUF_POOL_SIZE: the number of buffers in the pbuf pool. */
#define PBUF_POOL_SIZE          MEMP_NUM_PBUF

/* PBUF_POOL_BUFSIZE: the size of each pbuf in the pbuf pool. */
#define PBUF_POOL_BUFSIZE       LWIP_MEM_ALIGN_SIZE(TCP_MSS + 40 + 
PBUF_LINK_HLEN)

/* ---------- Netbuf options ---------- */
/* MEMP_NUM_NETBUF: the number of struct netbufs.*/
#define MEMP_NUM_NETBUF         6

/* MEMP_NUM_NETCONN: the number of struct netconns.*/
#define MEMP_NUM_NETCONN        6


As far as I understand the SSL will read a buffer decrypt it and return from 
ssl_read with the decrypted data.

The SSL function ssl_read does not know in advance (I think) how many bytes are 
there to decrypt. So if it
Works for a small message it should work for a larger message that is decrypted 
in chunks anyway.

Any suggestion for an easy to handle (for testing) WSS server in PHP or similar 
?

I think you are correct that it is a memory problem or some tweaking issue but 
I am not sure what ?

Anymore hints will be welcomed :-) 


BR,
Noam.



-----Original Message-----
From: lwip-users [mailto:address@hidden On Behalf Of Jan Menzel
Sent: Wednesday, March 01, 2017 5:13 PM
To: address@hidden
Subject: Re: [lwip-users] PolarSSL and mbedTLS

Hi Noam!
        I've designed a system with almost the same setup which works well 
since a few years incl. firmware updates of a ~200kb.
        Did you checked the memory consumption of the ip stack and the ssl max 
content length setting? The default max content length setting is IIRC 16kb, 
which means that data is hashed and encrypted in chunks of up to 16kb and can 
only be verified and decrypted once the entire chunk has been received. The 
firmware update on my system only works if the max content length is reduced. 
With the default setting I faced memory issues on LPC1768 (which has just a 
fraction of your F4xx).
        I also had to fiddle around a little bit with errno in the interface 
between mbedtls and lwip. One last advice: carefully check your stack usage. 
mbedtls uses lots of function pointers which Keils static call graph analysis 
can not see and does not warn about.

        Jan

On 01.03.2017 14:01, Noam Weissman wrote:
> Hi,
> 
>  
> 
> I have a client, single task using the socket API using and also 
> PolarSSL for SSL support.
> 
>  
> 
> The client is WebSocket client and all seems to work ok.
> 
>  
> 
> When I try to send small messages from the server to my client all is 
> working ok but when I try to push a large
> 
> message 6K and up my ssl_read function fails with a read error?.
> 
>  
> 
> The ssl_read is actually calling lwip_read internally.
> 
>  
> 
> For some reason the SSL code is trying to read a large buffer 8-16K 
> bytes and the read function fails.
> 
>  
> 
> Normally when we read from a socket more than is available the return 
> value should be the number
> 
> of bytes actually read and not an error ?.
> 
>  
> 
> The processor is STM32F427 using CCM for heap and Keil IDE
> 
>  
> 
> My main project uses Lwip 1.41, FreeRTOS 8.0.1 and PolarSSL 1.0.0
> 
>  
> 
> I have created two almost identical projects to the one I use. The 
> first
> uses:
> 
> Lwip 2.01, FreeRTOS 9.0
> 
>  
> 
> The second project is the same as the one with Lwip 2.01 but instead 
> of PolaSSL I switched to mbedTLS 2.4.0
> 
>  
> 
> In none secure mode everything works as expected and have no problems 
> getting a large message (600K)
> 
> In secured mode I get a read fail on the first packet ??
> 
>  
> 
> Anyone has an idea what I am doing wrong or what setting are not correct ??
> 
>  
> 
> A second question for Simon or anyone that can assist. I tried to set 
> LWIP_DEBUG to 1 and my total used RAM (compiler) dropped
> 
> about 30K ?? Why is that ?... I understood that debug should take more 
> RAM not Less ?
> 
>  
> 
> Thanks,
> 
> Noam.
> 
>  
> 
> cid:image001.jpg@01D26A92.68494F10
> 
>       
> 
> Noam Weissman
> 
> Software Engineer
> 
> SILORA R&D
> 
> p:
> 
>       
> 
> +972-4-9554915 m: +972-52-5786135
> 
> w:
> 
>       
> 
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> 
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