ipc: add semget syscall wrapper

Provide ksys_semget() wrapper to avoid in-kernel calls to this syscall.
The ksys_ prefix denotes that this function is meant as a drop-in
replacement for the syscall. In particular, it uses the same calling
convention as sys_semget().

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

3 files changed, 9 insertions, 3 deletions

diff --git a/ipc/sem.c b/ipc/sem.c
index e21ceb8b4af1..2e5f7ec7a7db 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -556,7 +556,7 @@ static inline int sem_more_checks(struct kern_ipc_perm *ipcp,
         return 0;
 }
 
-SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
+long ksys_semget(key_t key, int nsems, int semflg)
 {
         struct ipc_namespace *ns;
         static const struct ipc_ops sem_ops = {
@@ -578,6 +578,11 @@ SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
         return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
 }
 
+SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
+{
+        return ksys_semget(key, nsems, semflg);
+}
+
 /**
  * perform_atomic_semop[_slow] - Attempt to perform semaphore
  *                               operations on a given array.
diff --git a/ipc/syscall.c b/ipc/syscall.c
index 84d6a7691baa..21fcdf0b4836 100644
--- a/ipc/syscall.c
+++ b/ipc/syscall.c
@@ -35,7 +35,7 @@ SYSCALL_DEFINE6(ipc, unsigned int, call, int, first, unsigned long, second,
                                        (const struct timespec __user *)fifth);
 
         case SEMGET:
-                return sys_semget(first, second, third);
+                return ksys_semget(first, second, third);
         case SEMCTL: {
                 unsigned long arg;
                 if (!ptr)
@@ -132,7 +132,7 @@ COMPAT_SYSCALL_DEFINE6(ipc, u32, call, int, first, int, second,
                 return compat_ksys_semtimedop(first, compat_ptr(ptr), second,
                                                 compat_ptr(fifth));
         case SEMGET:
-                return sys_semget(first, second, third);
+                return ksys_semget(first, second, third);
         case SEMCTL:
                 if (!ptr)
                         return -EINVAL;
diff --git a/ipc/util.h b/ipc/util.h
index 6deadf77547e..0f07056e5a73 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -240,6 +240,7 @@ static inline int compat_ipc_parse_version(int *cmd)
 long ksys_semtimedop(int semid, struct sembuf __user *tsops,
                      unsigned int nsops,
                      const struct timespec __user *timeout);
+long ksys_semget(key_t key, int nsems, int semflg);
 
 /* for CONFIG_ARCH_WANT_OLD_COMPAT_IPC */
 #ifdef CONFIG_COMPAT