linux-kernel - [PATCH 3.16 215/366] ALSA: hda: Hardening for potential Spectre v1

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Message-ID: <lsq.1539530741.110311854@decadent.org.uk>
Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Dan Carpenter" <dan.carpenter@...cle.com>,
        "Takashi Iwai" <tiwai@...e.de>
Subject: [PATCH 3.16 215/366] ALSA: hda: Hardening for potential Spectre v1

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@...e.de>

commit 69fa6f19b95597618ab30438a27b67ad93daa7c7 upstream.

As recently Smatch suggested, one place in HD-audio hwdep ioctl codes
may expand the array directly from the user-space value with
speculation:
  sound/pci/hda/hda_local.h:467 get_wcaps() warn: potential spectre issue 'codec->wcaps'

As get_wcaps() itself is a fairly frequently called inline function,
and there is only one single call with a user-space value, we replace
only the latter one to open-code locally with array_index_nospec()
hardening in this patch.

BugLink: https://marc.info/?l=linux-kernel&m=152411496503418&w=2
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
[bwh: Backported to 3.16: s/core\.//g]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 sound/pci/hda/hda_hwdep.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/sound/pci/hda/hda_hwdep.c
+++ b/sound/pci/hda/hda_hwdep.c
@@ -21,6 +21,7 @@
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/compat.h>
+#include <linux/nospec.h>
 #include <sound/core.h>
 #include "hda_codec.h"
 #include "hda_local.h"
@@ -51,7 +52,16 @@ static int get_wcap_ioctl(struct hda_cod
 	
 	if (get_user(verb, &arg->verb))
 		return -EFAULT;
-	res = get_wcaps(codec, verb >> 24);
+	/* open-code get_wcaps(verb>>24) with nospec */
+	verb >>= 24;
+	if (verb < codec->start_nid ||
+	    verb >= codec->start_nid + codec->num_nodes) {
+		res = 0;
+	} else {
+		verb -= codec->start_nid;
+		verb = array_index_nospec(verb, codec->num_nodes);
+		res = codec->wcaps[verb];
+	}
 	if (put_user(res, &arg->res))
 		return -EFAULT;
 	return 0;