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>

1 files changed, 5 insertions, 4 deletions

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();