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Re: [Qemu-devel] QEMU soundcards vulnerable to jack retasking?

From: Gerd Hoffmann
Subject: Re: [Qemu-devel] QEMU soundcards vulnerable to jack retasking?
Date: Mon, 28 Nov 2016 11:30:14 +0100

On Fr, 2016-11-25 at 21:25 +0100, address@hidden wrote:
> Recent security research shows that soundcards support surreptitiously 
> switching line-out jacks into line-in by modifying the software stack. 
> The way modern speakers and headphones are designed makes them readily 
> usable as microphones. The Intel High Definition (HD) Audio standards 
> which all modern consumer soundcards are based mandates this stupidity.
> https://arxiv.org/ftp/arxiv/papers/1611/1611.07350.pdf
> Does anyone know if QEMU's emulated sound devices follow this standard? 

No.  Output line is output only and input line is input only, period.

There are three qemu hda codecs available:

    only playback (line-out).  No way the guest can record anything.

    record (line-in) and playback (line-out).  Use that if you need
    sound recording in the guest.

    record (micro) and playback (speaker).  Same as hda-duplex, except
    that the record and playback channels are tagged differently.  Use
    that if your guests app is picky and refuses to record from line-in.

Where the data for the record channel comes from is subject to host
configuration.  On a typical linux system it'll probably being
pulseaudio, either directly or indirectly (via spice).


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