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Commit ec67aaa4 authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Linus Torvalds
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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: default avatarDavidlohr Bueso <dbueso@suse.de>
Reported-by: default avatarDan 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f1b4bd06

ipc/sem.c

+14 −4
Original line number Diff line number Diff line
@@ -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) {