x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt_disable()

Add preempt_disable() + preempt_enable() around math_state_restore() in
__restore_xstate_sig(). Otherwise __switch_to() after __thread_fpu_begin()
can overwrite fpu->state we are going to restore.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/20140902175717.GA21649@redhat.com
Cc: <stable@vger.kernel.org> # v3.7+
Reviewed-by: Suresh Siddha <sbsiddha@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index cf0b83040ec8..4c540c4719d8 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -400,8 +400,11 @@ int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
                         set_used_math();
                 }
 
-                if (use_eager_fpu())
+                if (use_eager_fpu()) {
+                        preempt_disable();
                         math_state_restore();
+                        preempt_enable();
+                }
 
                 return err;
         } else {