microblaze: fix clone syscall

Fix inadvertent breakage in the clone syscall ABI for Microblaze that
was introduced in commit f3268edbe6fe ("microblaze: switch to generic
fork/vfork/clone").

The Microblaze syscall ABI for clone takes the parent tid address in the
4th argument; the third argument slot is used for the stack size.  The
incorrectly-used CLONE_BACKWARDS type assigned parent tid to the 3rd
slot.

This commit restores the original ABI so that existing userspace libc
code will work correctly.

All kernel versions from v3.8-rc1 were affected.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 18 insertions, 1 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index 8d2ae24b9f4a..1feb169274fe 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -407,6 +407,12 @@ config CLONE_BACKWARDS2
         help
           Architecture has the first two arguments of clone(2) swapped.
 
+config CLONE_BACKWARDS3
+        bool
+        help
+          Architecture has tls passed as the 3rd argument of clone(2),
+          not the 5th one.
+
 config ODD_RT_SIGACTION
         bool
         help
diff --git a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
index d22a4ecffff4..4fab52294d98 100644
--- a/arch/microblaze/Kconfig
+++ b/arch/microblaze/Kconfig
@@ -28,7 +28,7 @@ config MICROBLAZE
         select GENERIC_CLOCKEVENTS
         select GENERIC_IDLE_POLL_SETUP
         select MODULES_USE_ELF_RELA
-        select CLONE_BACKWARDS
+        select CLONE_BACKWARDS3
 
 config SWAP
         def_bool n
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 4147d700a293..84662ecc7b51 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -802,9 +802,14 @@ asmlinkage long sys_vfork(void);
 asmlinkage long sys_clone(unsigned long, unsigned long, int __user *, int,
                int __user *);
 #else
+#ifdef CONFIG_CLONE_BACKWARDS3
+asmlinkage long sys_clone(unsigned long, unsigned long, int, int __user *,
+                          int __user *, int);
+#else
 asmlinkage long sys_clone(unsigned long, unsigned long, int __user *,
                int __user *, int);
 #endif
+#endif
 
 asmlinkage long sys_execve(const char __user *filename,
                 const char __user *const __user *argv,
diff --git a/kernel/fork.c b/kernel/fork.c
index 403d2bb8a968..e23bb19e2a3e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1679,6 +1679,12 @@ SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
                  int __user *, parent_tidptr,
                  int __user *, child_tidptr,
                  int, tls_val)
+#elif defined(CONFIG_CLONE_BACKWARDS3)
+SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
+                int, stack_size,
+                int __user *, parent_tidptr,
+                int __user *, child_tidptr,
+                int, tls_val)
 #else
 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
                  int __user *, parent_tidptr,