From: Davidlohr Bueso <dave@xxxxxxxxxxxx> Subject: 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@xxxxxxx> Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: "Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx> Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- ipc/sem.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff -puN ipc/sem.c~ipc-sem-mitigate-semnum-index-against-spectre-v1 ipc/sem.c --- a/ipc/sem.c~ipc-sem-mitigate-semnum-index-against-spectre-v1 +++ a/ipc/sem.c @@ -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_ar 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_ar * * 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(str 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 s * 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_name 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_namesp 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, str */ 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) { _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
