[PATCH] ipmi: msghandler: Fix potential Spectre v1 vulnerabilities

[Gustavo A. R. Silva]

channel and addr->channel are indirectly controlled by user-space,
hence leading to a potential exploitation of the Spectre variant 1
vulnerability.

These issues were detected with the help of Smatch:

drivers/char/ipmi/ipmi_msghandler.c:1381 ipmi_set_my_address() warn: potential spectre issue 'user->intf->addrinfo' [w] (local cap)
drivers/char/ipmi/ipmi_msghandler.c:1401 ipmi_get_my_address() warn: potential spectre issue 'user->intf->addrinfo' [r] (local cap)
drivers/char/ipmi/ipmi_msghandler.c:1421 ipmi_set_my_LUN() warn: potential spectre issue 'user->intf->addrinfo' [w] (local cap)
drivers/char/ipmi/ipmi_msghandler.c:1441 ipmi_get_my_LUN() warn: potential spectre issue 'user->intf->addrinfo' [r] (local cap)
drivers/char/ipmi/ipmi_msghandler.c:2260 check_addr() warn: potential spectre issue 'intf->addrinfo' [r] (local cap)

Fix this by sanitizing channel and addr->channel before using them to
index user->intf->addrinfo and intf->addrinfo, correspondingly.

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://lore.kernel.org/lkml/20180423164740.GY17484@xxxxxxxxxxxxxx/

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
---
 drivers/char/ipmi/ipmi_msghandler.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index 480d9bd7e1ab..557e98d9364d 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -32,6 +32,7 @@
 #include <linux/moduleparam.h>
 #include <linux/workqueue.h>
 #include <linux/uuid.h>
+#include <linux/nospec.h>
 
 #define IPMI_DRIVER_VERSION "39.2"
 
@@ -1375,10 +1376,12 @@ int ipmi_set_my_address(struct ipmi_user *user,
 	if (!user)
 		return -ENODEV;
 
-	if (channel >= IPMI_MAX_CHANNELS)
+	if (channel >= IPMI_MAX_CHANNELS) {
 		rv = -EINVAL;
-	else
+	} else {
+		channel = array_index_nospec(channel, IPMI_MAX_CHANNELS);
 		user->intf->addrinfo[channel].address = address;
+	}
 	release_ipmi_user(user, index);
 
 	return rv;
@@ -1395,10 +1398,12 @@ int ipmi_get_my_address(struct ipmi_user *user,
 	if (!user)
 		return -ENODEV;
 
-	if (channel >= IPMI_MAX_CHANNELS)
+	if (channel >= IPMI_MAX_CHANNELS) {
 		rv = -EINVAL;
-	else
+	} else {
+		channel = array_index_nospec(channel, IPMI_MAX_CHANNELS);
 		*address = user->intf->addrinfo[channel].address;
+	}
 	release_ipmi_user(user, index);
 
 	return rv;
@@ -1415,10 +1420,12 @@ int ipmi_set_my_LUN(struct ipmi_user *user,
 	if (!user)
 		return -ENODEV;
 
-	if (channel >= IPMI_MAX_CHANNELS)
+	if (channel >= IPMI_MAX_CHANNELS) {
 		rv = -EINVAL;
-	else
+	} else {
+		channel = array_index_nospec(channel, IPMI_MAX_CHANNELS);
 		user->intf->addrinfo[channel].lun = LUN & 0x3;
+	}
 	release_ipmi_user(user, index);
 
 	return rv;
@@ -1435,10 +1442,12 @@ int ipmi_get_my_LUN(struct ipmi_user *user,
 	if (!user)
 		return -ENODEV;
 
-	if (channel >= IPMI_MAX_CHANNELS)
+	if (channel >= IPMI_MAX_CHANNELS) {
 		rv = -EINVAL;
-	else
+	} else {
+		channel = array_index_nospec(channel, IPMI_MAX_CHANNELS);
 		*address = user->intf->addrinfo[channel].lun;
+	}
 	release_ipmi_user(user, index);
 
 	return rv;
@@ -2257,6 +2266,7 @@ static int check_addr(struct ipmi_smi  *intf,
 {
 	if (addr->channel >= IPMI_MAX_CHANNELS)
 		return -EINVAL;
+	addr->channel = array_index_nospec(addr->channel, IPMI_MAX_CHANNELS);
 	*lun = intf->addrinfo[addr->channel].lun;
 	*saddr = intf->addrinfo[addr->channel].address;
 	return 0;
-- 
2.20.1