[PATCH 0/2] audio: prevent a class of guest-triggered aborts

[Volker Rümelin]

The issues with guest-triggered aborts started with commit ab32b78cd1 
"audio: Simplify audio_bug() removing old code" which introduced an 
abort() in function audio_bug(). The abort() was there before, but it 
was only compiled in for debugging purposes.

After this commit issue https://bugs.launchpad.net/bugs/1910603 showed 
up. This bug was mitigated with commits a2cd86a94a ("hw/audio/sb16: 
Avoid assertion by restricting I/O sampling rate range") and 60e543f5ce 
("hw/audio/sb16: Restrict I/O sampling rate range for command 41h/42h"). 
The issue was only mitigated because I can still trigger the same abort.

To reproduce start a FreeDOS QEMU guest with:

./qemu-system-i386 -machine pc,pcspk-audiodev=audio0 \
 -device sb16,audiodev=audio0 \
 -audiodev 
pa,id=audio0,timer-period=170,out.mixing-engine=on,out.buffer-length=181 \
 -drive ...

On the guest enter the out port sequence from launchpad bug #1910603:
C:\> debug
-o 22c 41
-o 22c 0
-o 22c 4
-o 22c 1c

On the host:
A bug was just triggered in audio_calloc
Save all your work and restart without audio
I am sorry
Context:
audio_pcm_sw_alloc_resources_out passed invalid arguments to audio_calloc
nmemb=0 size=16 (len=0)
Aborted (core dumped)

Here is another example to trigger the same abort. Start a Linux guest 
with an AC97 audio device:

./qemu-system-x86_64 -machine q35,pcspk-audiodev=audio0 \
 -device AC97,bus=pcie.0,addr=0x1b,audiodev=audio0 \
 -audiodev pa,id=audio0 \
 - ...

Open a shell on the guest:
~>sudo lspci -s '00:1b.0' -nn -vv
00:1b.0 Multimedia audio controller [0401]: Intel Corporation 82801AA 
AC'97 Audio Controller [8086:2415] (rev 01)
    Subsystem: Red Hat, Inc. QEMU Virtual Machine [1af4:1100]
    Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx-
    Status: Cap- 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- 
<TAbort- <MAbort- >SERR- <PERR- INTx-
    Latency: 0
    Interrupt: pin A routed to IRQ 16
    Region 0: I/O ports at c000 [size=1K]
    Region 1: I/O ports at c400 [size=256]
    Kernel driver in use: snd_intel8x0
    Kernel modules: snd_intel8x0

~># IOBAR0 + 0x2c
~>sudo outw 0xc02c 1

On the host:
A bug was just triggered in audio_calloc
Save all your work and restart without audio
I am sorry
Context:
audio_pcm_sw_alloc_resources_out passed invalid arguments to audio_calloc
nmemb=0 size=16 (len=0)
Aborted (core dumped)

Remove the abort() in audio_bug() to avoid this class of guest-triggered 
aborts.

Volker Rümelin (2):
  Revert "audio: Log context for audio bug"
  audio: remove abort() in audio_bug()

 audio/audio.c          | 24 ++++++++++++------------
 audio/audio_template.h | 27 +++++++++++++++------------
 2 files changed, 27 insertions(+), 24 deletions(-)

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2.35.3