ipc: add COMPAT_SHMLBA support

If the SHMLBA definition for a native task differs from the definition for
a compat task, the do_shmat() function would need to handle both.

This patch introduces COMPAT_SHMLBA, which is used by the compat shmat
syscall when calling the ipc code and allows architectures such as AArch64
(where the native SHMLBA is 64k but the compat (AArch32) definition is
16k) to provide the correct semantics for compat IPC system calls.

Cc: David S. Miller <davem@davemloft.net>
Cc: Chris Zankel <chris@zankel.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 12 insertions, 7 deletions

diff --git a/ipc/compat.c b/ipc/compat.c
index a6df704f521e..53cebdf80e3c 100644
--- a/ipc/compat.c
+++ b/ipc/compat.c
@@ -514,6 +514,10 @@ long compat_sys_msgctl(int first, int second, void __user *uptr)
         return err;
 }
 
+#ifndef COMPAT_SHMLBA
+#define COMPAT_SHMLBA   SHMLBA
+#endif
+
 #ifdef CONFIG_ARCH_WANT_OLD_COMPAT_IPC
 long compat_sys_shmat(int first, int second, compat_uptr_t third, int version,
                         void __user *uptr)
@@ -524,7 +528,7 @@ long compat_sys_shmat(int first, int second, compat_uptr_t third, int version,
 
         if (version == 1)
                 return -EINVAL;
-        err = do_shmat(first, uptr, second, &raddr);
+        err = do_shmat(first, uptr, second, &raddr, COMPAT_SHMLBA);
         if (err < 0)
                 return err;
         uaddr = compat_ptr(third);
@@ -536,7 +540,7 @@ long compat_sys_shmat(int shmid, compat_uptr_t shmaddr, int shmflg)
         unsigned long ret;
         long err;
 
-        err = do_shmat(shmid, compat_ptr(shmaddr), shmflg, &ret);
+        err = do_shmat(shmid, compat_ptr(shmaddr), shmflg, &ret, COMPAT_SHMLBA);
         if (err)
                 return err;
         force_successful_syscall_return();
diff --git a/ipc/shm.c b/ipc/shm.c
index 41c1285d697a..00faa05cf72a 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -953,7 +953,8 @@ out:
  * "raddr" thing points to kernel space, and there has to be a wrapper around
  * this.
  */
-long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
+long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
+              unsigned long shmlba)
 {
         struct shmid_kernel *shp;
         unsigned long addr;
@@ -973,9 +974,9 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
         if (shmid < 0)
                 goto out;
         else if ((addr = (ulong)shmaddr)) {
-                if (addr & (SHMLBA-1)) {
+                if (addr & (shmlba - 1)) {
                         if (shmflg & SHM_RND)
-                                addr &= ~(SHMLBA-1);       /* round down */
+                                addr &= ~(shmlba - 1);     /* round down */
                         else
 #ifndef __ARCH_FORCE_SHMLBA
                                 if (addr & ~PAGE_MASK)
@@ -1107,7 +1108,7 @@ SYSCALL_DEFINE3(shmat, int, shmid, char __user *, shmaddr, int, shmflg)
         unsigned long ret;
         long err;
 
-        err = do_shmat(shmid, shmaddr, shmflg, &ret);
+        err = do_shmat(shmid, shmaddr, shmflg, &ret, SHMLBA);
         if (err)
                 return err;
         force_successful_syscall_return();
diff --git a/ipc/syscall.c b/ipc/syscall.c
index 1d6f53f6b562..0d1e32ce048e 100644
--- a/ipc/syscall.c
+++ b/ipc/syscall.c
@@ -73,7 +73,7 @@ SYSCALL_DEFINE6(ipc, unsigned int, call, int, first, unsigned long, second,
                 default: {
                         unsigned long raddr;
                         ret = do_shmat(first, (char __user *)ptr,
-                                       second, &raddr);
+                                       second, &raddr, SHMLBA);
                         if (ret)
                                 return ret;
                         return put_user(raddr, (unsigned long __user *) third);