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sysvipc/sem: mitigate semnum index against spectre v1 

Both smatch and coverity are reporting potential issues with spectre
variant 1 with the 'semnum' index within the sma->sems array, ie:

  ipc/sem.c:388 sem_lock() warn: potential spectre issue 'sma->sems'
  ipc/sem.c:641 perform_atomic_semop_slow() warn: potential spectre issue 'sma->sems'
  ipc/sem.c:721 perform_atomic_semop() warn: potential spectre issue 'sma->sems'

Avoid any possible speculation by using array_index_nospec() thus
ensuring the semnum value is bounded to [0, sma->sem_nsems).  With the
exception of sem_lock() all of these are slowpaths.

Link: http://lkml.kernel.org/r/20180423171131.njs4rfm2yzyeg6do@linux-n805
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Davidlohr Bueso 2018-06-14 15:27:51 -07:00 committed by Linus Torvalds
parent f1b4bd0676
commit ec67aaa46d
1 changed files with 14 additions and 4 deletions
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18
ipc/sem.c
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@ -85,6 +85,7 @@
#include <linux/nsproxy.h>
#include <linux/ipc_namespace.h>
#include <linux/sched/wake_q.h>
#include <linux/nospec.h>
#include <linux/uaccess.h>
#include "util.h"
@ -368,6 +369,7 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
int nsops)
{
struct sem *sem;
int idx;
if (nsops != 1) {
/* Complex operation - acquire a full lock */
@ -385,7 +387,8 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
*
* Both facts are tracked by use_global_mode.
*/
sem = &sma->sems[sops->sem_num];
idx = array_index_nospec(sops->sem_num, sma->sem_nsems);
sem = &sma->sems[idx];
/*
* Initial check for use_global_lock. Just an optimization,
@ -638,7 +641,8 @@ static int perform_atomic_semop_slow(struct sem_array *sma, struct sem_queue *q)
un = q->undo;
for (sop = sops; sop < sops + nsops; sop++) {
curr = &sma->sems[sop->sem_num];
int idx = array_index_nospec(sop->sem_num, sma->sem_nsems);
curr = &sma->sems[idx];
sem_op = sop->sem_op;
result = curr->semval;
@ -718,7 +722,9 @@ static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
* until the operations can go through.
*/
for (sop = sops; sop < sops + nsops; sop++) {
curr = &sma->sems[sop->sem_num];
int idx = array_index_nospec(sop->sem_num, sma->sem_nsems);
curr = &sma->sems[idx];
sem_op = sop->sem_op;
result = curr->semval;
@ -1356,6 +1362,7 @@ static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
return -EIDRM;
}
semnum = array_index_nospec(semnum, sma->sem_nsems);
curr = &sma->sems[semnum];
ipc_assert_locked_object(&sma->sem_perm);
@ -1509,6 +1516,8 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
err = -EIDRM;
goto out_unlock;
}
semnum = array_index_nospec(semnum, nsems);
curr = &sma->sems[semnum];
switch (cmd) {
@ -2081,7 +2090,8 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops,
*/
if (nsops == 1) {
struct sem *curr;
curr = &sma->sems[sops->sem_num];
int idx = array_index_nospec(sops->sem_num, sma->sem_nsems);
curr = &sma->sems[idx];
if (alter) {
if (sma->complex_count) {