[Z/A/linux-eom][PATCH] ALSA: hda: Abort capability probe at invalid register read

Hui Wang hui.wang at canonical.com
Mon Nov 6 03:52:30 UTC 2017

From: Takashi Iwai <tiwai at suse.de>

BugLink: http://bugs.launchpad.net/bugs/1730261

The loop in snd_hdac_bus_parse_capabilities() may go to nirvana when
it hits an invalid register value read:

 BUG: unable to handle kernel paging request at ffffad5dc41f3fff
 IP: pci_azx_readl+0x5/0x10 [snd_hda_intel]
 Call Trace:
  snd_hdac_bus_parse_capabilities+0x3c/0x1f0 [snd_hda_core]
  azx_probe_continue+0x7d5/0x940 [snd_hda_intel]

This happened on a new Intel machine, and we need to check the value
and abort the loop accordingly.

[Note: the fixes tag below indicates only the commit where this patch
 can be applied; the original problem was introduced even before that

Fixes: 6720b38420a0 ("ALSA: hda - move bus_parse_capabilities to core")
Cc: <stable at vger.kernel.org>
Acked-by: Vinod Koul <vinod.koul at intel.com>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
(cherry picked from commit 098a0a62c1554f5a3813ef1b8539563214ada8f6)
Signed-off-by: Hui Wang <hui.wang at canonical.com>
 sound/hda/hdac_controller.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sound/hda/hdac_controller.c b/sound/hda/hdac_controller.c
index 978dc18..f6d2985 100644
--- a/sound/hda/hdac_controller.c
+++ b/sound/hda/hdac_controller.c
@@ -284,6 +284,11 @@ int snd_hdac_bus_parse_capabilities(struct hdac_bus *bus)
 		dev_dbg(bus->dev, "HDA capability ID: 0x%x\n",
 			(cur_cap & AZX_CAP_HDR_ID_MASK) >> AZX_CAP_HDR_ID_OFF);
+		if (cur_cap == -1) {
+			dev_dbg(bus->dev, "Invalid capability reg read\n");
+			break;
+		}
 		switch ((cur_cap & AZX_CAP_HDR_ID_MASK) >> AZX_CAP_HDR_ID_OFF) {
 		case AZX_ML_CAP_ID:
 			dev_dbg(bus->dev, "Found ML capability\n");

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