Commit 088e861e authored Apr 24, 2018 by Takashi Iwai

ALSA: control: Hardening for potential Spectre v1

As recently Smatch suggested, a few places in ALSA control core codes
may expand the array directly from the user-space value with
speculation:

sound/core/control.c:1003 snd_ctl_elem_lock() warn: potential spectre issue 'kctl->vd'
sound/core/control.c:1031 snd_ctl_elem_unlock() warn: potential spectre issue 'kctl->vd'
sound/core/control.c:844 snd_ctl_elem_info() warn: potential spectre issue 'kctl->vd'
sound/core/control.c:891 snd_ctl_elem_read() warn: potential spectre issue 'kctl->vd'
sound/core/control.c:939 snd_ctl_elem_write() warn: potential spectre issue 'kctl->vd'

Although all these seem doing only the first load without further
reference, we may want to stay in a safer side, so hardening with
array_index_nospec() would still make sense.

In this patch, we put array_index_nospec() to the common
snd_ctl_get_ioff*() helpers instead of each caller. These helpers are
also referred from some drivers, too, and basically all usages are to
calculate the array index from the user-space value, hence it's better
to cover there.

BugLink: https://marc.info/?l=linux-kernel&m=152411496503418&w=2

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

parent 8d218dd8

include/sound/control.h

+5 −2

Original line number	Diff line number	Diff line
		@@ -23,6 +23,7 @@
		*/

		#include <linux/wait.h>
		#include <linux/nospec.h>
		#include <sound/asound.h>

		#define snd_kcontrol_chip(kcontrol) ((kcontrol)->private_data)
		@@ -148,12 +149,14 @@ int snd_ctl_get_preferred_subdevice(struct snd_card *card, int type);

		static inline unsigned int snd_ctl_get_ioffnum(struct snd_kcontrol kctl, struct snd_ctl_elem_id id)
		{
		return id->numid - kctl->id.numid;
		unsigned int ioff = id->numid - kctl->id.numid;
		return array_index_nospec(ioff, kctl->count);
		}

		static inline unsigned int snd_ctl_get_ioffidx(struct snd_kcontrol kctl, struct snd_ctl_elem_id id)
		{
		return id->index - kctl->id.index;
		unsigned int ioff = id->index - kctl->id.index;
		return array_index_nospec(ioff, kctl->count);
		}

		static inline unsigned int snd_ctl_get_ioff(struct snd_kcontrol kctl, struct snd_ctl_elem_id id)

Admin message