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[20160521] Catching up: audio-mixing, arm, x86 and amd64 platform improvements and security
A few noteworthy things have happened in NetBSD land, and being lazy I will collect them in one blog posting. Here we go:
  • In-kernel audio mixing: So far, NetBSD's audio device can only be opened once. If more than one application wants to play sound, the first one wins. This is suboptimal if you want to (say) play some MP3s but also get some occasional noise from your webbrowser.

    Now, Nathanial Sloss has made a stab at this, providing several implementation choices. Challenges in the task are that sounds with different quality (sampling rate, mono/stereo etc.) need to be brought to one common quality before mixing and passing on to the actual audio hardware. Further fun is added by the delay this process adds. See the discussion on tech-kern for all the gory details!

  • Freescale i.MX7 support: Ryo Shimizu has committed support for the Freescale i.MX7 processor and the Atmark Techno Armadillo-IoT G3 board. according to his posting to port-arm (dmesg included), UART, Ethernet, USB, SDHC, RTC, GPIO, WDOG and MULTIPROCESSOR work. Interesting thing of the platform is that is has two Cortex-A7 cores and one Cortex-M4 core, the latter without MMU. Ideas on how to use the latter are welcome! :)

  • PIE binaries with PaX, ASLR+MPROTECT are now the default for i386. ASLR and MPROTECT can be turned off either globally or per-binary if any problems should arise. Be sure to document those exceptions in your risk management! :-)

    More information: PaX, PIE, ASLR, MPROTECT.

  • Platform improvements for i386 and amd64. For amd64, Maxime Villard writes:
     - I cleaned up the asm code and fixed several comments, which makes the
       boot process much easier to understand.
     - I fixed the alignment for the text segment, so that it can be covered by
       more large pages [1] - thereby reducing TLB contention.
     - I fixed a bug in the way the secondary CPUs are launched [2], which
       caused them to crash if they tried to access an X-less page.
     - I took rodata out of the text+rodata chunk, and put it in the data+bss+
       PRELOADED_MODULES+BOOTSTRAP_TABLES chunk [3]. rodata was no longer large
       page optimized, and had RWX permissions.
     - I retook rodata out of the rodata+data+bss+PRELOADED_MODULES+
       BOOTSTRAP_TABLES chunk, and made the kernel map it independently without
       the W permision [4].
     - I made the kernel map rodata without the X permission, by using the NOX
       bit on its pages [5] (now that the secondary CPUs could handle that
       properly).
     - I took the data+bss chunk out of the data+bss+PRELOADED_MODULES+
       BOOTSTRAP_TABLES chunk, and made the kernel map it independently without
       X permission [6].
     - I made the kernel remap rodata and data+bss with large pages and proper
       permissions [7] - which reduces once again TLB contention.
    
    See Maxime's posting to tech-kern for all the footnotes. Likewise, Maxime also tackled i386, and besides the changes from amd64, here is the list of changes from his email:
     - on non-PAE i386, NOX does not exist. Therefore the mappings all have an
       additional X permission. To benefit from X-less mappings, your CPU must
       support PAE, and your kernel must be GENERIC_PAE.
     - the segments are not large-page-aligned, which means that probably some
       parts of the segments are still mapped with normal pages. It is still more
       optimized than it used to be, but not as much as amd64 is.
    


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