8000 esp32: mbedtls can't allocate in/out buffers on IDF4.x · Issue #5303 · micropython/micropython · GitHub
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jimmo opened this issue Nov 7, 2019 · 4 comments
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esp32: mbedtls can't allocate in/out buffers on IDF4.x #5303

jimmo opened this issue Nov 7, 2019 · 4 comments
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port-esp32

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@jimmo
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jimmo commented Nov 7, 2019

Raised at https://forum.micropython.org/viewtopic.php?f=18&t=7208

At the point that modussl_mbedtls.c calls mbedtls_ssl_setup, the ESP32 heap looks like this:

Heap summary for capabilities 0x00001800:
  At 0x3ffaff10 len 240 free 0 allocated 168 min_free 0
    largest_free_block 0 alloc_blocks 10 free_blocks 0 total_blocks 10
  At 0x3ffb6388 len 7288 free 0 allocated 7168 min_free 0
    largest_free_block 0 alloc_blocks 22 free_blocks 0 total_blocks 22
  At 0x3ffb9a20 len 16648 free 0 allocated 16324 min_free 0
    largest_free_block 0 alloc_blocks 73 free_blocks 0 total_blocks 73
  At 0x3ffcc870 len 79760 free 26808 allocated 52520 min_free 19840
    largest_free_block 26716 alloc_blocks 94 free_blocks 6 total_blocks 100
  At 0x3ffe0440 len 15072 free 15036 allocated 0 min_free 15036
    largest_free_block 15036 alloc_blocks 0 free_blocks 1 total_blocks 1
  At 0x3ffe4350 len 113840 free 4092 allocated 109708 min_free 4092
    largest_free_block 4092 alloc_blocks 1 free_blocks 1 total_blocks 2
  Totals:
    free 45936 allocated 185888 min_free 38968 largest_free_block 26716

mbedtls_ssl_setup tries to allocate two 16717 buffers -- the first (ssl->in_buf) succeeds (likely from the fourth block) then the second (ssl->out_buf ) fails.

Easy workaround would be to enable CONFIG_MBEDTLS_ASYMMETRIC_CONTENT_LEN (which would drop the output buffer to 4kiB).

I'll grab the heap info for a 3.3 build. I'm guessing that by chance the fragmentation across the blocks just ends up being slightly more favourable to two >16kiB allocations.
@dpgeorge
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dpgeorge commented Nov 7, 2019

I didn't know that it's possible to configure the in/out SSL content lengths separately in mbedtls. IMO it'd be good to enable this feature on all ports that use mbedtls, because otherwise SSL connections cost a lot of RAM (ie 16k for incoming, to support all servers, but 4k or so on outgoing data).

@jimmo
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jimmo commented Nov 7, 2019

OK, I will send a PR to do that.

However, looking at the heap summary in 3.3 (below) is quite interesting and clearly shows why this problem exists now -- there used to be a 154504 byte region in 3.3 which is now split into 79760 + 16648 + 15072 in 4.x.

Heap summary for capabilities 0x00001800:
  At 0x3ffae6e0 len 6432 free 0 allocated 6276 min_free 0
    largest_free_block 0 alloc_blocks 31 free_blocks 0 total_blocks 31
  At 0x3ffba478 len 154504 free 0 allocated 154120 min_free 0
    largest_free_block 0 alloc_blocks 88 free_blocks 0 total_blocks 88
  At 0x3ffe0440 len 15072 free 0 allocated 14968 min_free 0
    largest_free_block 0 alloc_blocks 18 free_blocks 0 total_blocks 18
  At 0x3ffe4350 len 113840 free 94508 allocated 19124 min_free 87416
    largest_free_block 94448 alloc_blocks 40 free_blocks 4 total_blocks 44
  Totals:
    free 94508 allocated 194488 min_free 87416 largest_free_block 94448

The 3.3 MicroPython heap is 115008 bytes which came from that now-split 154504 region. On 4.x the MicroPython heap (now 107136 bytes) comes from that 113840 byte region instead.

@jimmo
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jimmo commented Nov 7, 2019

A consequence of this fragmentation is that even though setting CONFIG_MBEDTLS_ASYMMETRIC_CONTENT_LEN fixes the reported issue, it will fail to allocate a second concurrent ssl socket. Whereas in 3.3 it could support two concurrent sockets (or 4 with CONFIG_MBEDTLS_ASYMMETRIC_CONTENT_LEN).

jimmo added a commit to jimmo/micropython that referenced this issue Nov 7, 2019
@jimmo
esp32: Resize SSL output buffer from 16 to 4 kiB.
d8c8188 
Fixes micropython#5303
jimmo added a commit to jimmo/micropython that referenced this issue Nov 7, 2019
@jimmo
stm32: Resize mbedtls output buffer from 16 to 4 kiB.
4e3d007 
Ref micropython#5303
@jimmo jimmo mentioned this issue Nov 7, 2019
Closed
dpgeorge pushed a commit that referenced this issue Nov 11, 2019
@jimmo @dpgeorge
esp32/boards/sdkconfig.base: Resize SSL output buffer from 16 to 4kiB.
71299d3 
The IDF heap is more fragmented with IDF 4 and mbedtls cannot allocate
enough RAM with 16+16kiB for both in and out buffers, so reduce output
buffer size.

Fixes issue #5303.
@dpgeorge
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It seems IDF 4 (in its current development state) uses quite a bit more RAM than IDF 3. That's a good reason to keep support for IDF 3, and look into #5282

The issue here with mbedtls allocation is fixed by 71299d3, so I'll close this issue.

@jimmo jimmo mentioned this issue Nov 24, 2019
Closed
dpgeorge pushed a commit that referenced this issue Dec 20, 2019
@jimmo @dpgeorge
stm32/mbedtls: Resize mbedtls output buffer from 16 down to 4 kiB.
90f2864 
To reduce the size of the SSL context on the heap.  See issue #5303.
@Carglglz Carglglz mentioned this issue Jan 16, 2020
Closed
alu96 pushed a commit to alu96/micropython that referenced this issue Mar 23, 2020
@jimmo @dpgeorge
esp32/boards/sdkconfig.base: Resize SSL output buffer from 16 to 4kiB.
5d96a63 
The IDF heap is more fragmented with IDF 4 and mbedtls cannot allocate
enough RAM with 16+16kiB for both in and out buffers, so reduce output
buffer size.

Fixes issue micropython#5303.
alu96 pushed a commit to alu96/micropython that referenced this issue Mar 23, 2020
stm32/mbedtls: Resize mbedtls output buffer from 16 down to 4 kiB.
a052587 
To reduce the size of the SSL context on the heap.  See issue micropython#5303.
c0d3z3r0 pushed a commit to c0d3z3r0/micropython that referenced this issue Apr 5, 2020
@jimmo @pfalcon
esp32/boards/sdkconfig.base: Resize SSL output buffer from 16 to 4kiB.
91bbdea 
The IDF heap is more fragmented with IDF 4 and mbedtls cannot allocate
enough RAM with 16+16kiB for both in and out buffers, so reduce output
buffer size.

Fixes issue micropython#5303.
c0d3z3r0 pushed a commit to c0d3z3r0/micropython that referenced this issue Apr 5, 2020
@jimmo @pfalcon
stm32/mbedtls: Resize mbedtls output buffer from 16 down to 4 kiB.
fe05a37 
To reduce the size of the SSL context on the heap.  See issue micropython#5303.
tannewt pushed a commit to tannewt/circuitpython that referenced this issue Sep 7, 2021
@hathach
Merge pull request micropython#5303 from kamtom480/tinyusb_update
d29a12c 
Update TinyUSB
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