x86, smap: Do not abuse the [f][x]rstor_checking() functions for user space

With SMAP, the [f][x]rstor_checking() functions are no longer usable
for user-space pointers by applying a simple __force cast.  Instead,
create new [f][x]rstor_user() functions which do the proper SMAP
magic.
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1343171129-2747-3-git-send-email-suresh.b.siddha@intel.com

arch/x86/include/asm/fpu-internal.h

@@ -181,11 +181,28 @@ static inline int fxrstor_checking(struct i387_fxsave_struct *fx)
 			  "m" (*fx));
 }
 
+static inline int fxrstor_user(struct i387_fxsave_struct __user *fx)
+{
+	if (config_enabled(CONFIG_X86_32))
+		return user_insn(fxrstor %[fx], "=m" (*fx), [fx] "m" (*fx));
+	else if (config_enabled(CONFIG_AS_FXSAVEQ))
+		return user_insn(fxrstorq %[fx], "=m" (*fx), [fx] "m" (*fx));
+
+	/* See comment in fpu_fxsave() below. */
+	return user_insn(rex64/fxrstor (%[fx]), "=m" (*fx), [fx] "R" (fx),
+			  "m" (*fx));
+}
+
 static inline int frstor_checking(struct i387_fsave_struct *fx)
 {
 	return check_insn(frstor %[fx], "=m" (*fx), [fx] "m" (*fx));
 }
 
+static inline int frstor_user(struct i387_fsave_struct __user *fx)
+{
+	return user_insn(frstor %[fx], "=m" (*fx), [fx] "m" (*fx));
+}
+
 static inline void fpu_fxsave(struct fpu *fpu)
 {
 	if (config_enabled(CONFIG_X86_32))

arch/x86/kernel/xsave.c

@@ -315,7 +315,7 @@ static inline int restore_user_xstate(void __user *buf, u64 xbv, int fx_only)
 		if ((unsigned long)buf % 64 || fx_only) {
 			u64 init_bv = pcntxt_mask & ~XSTATE_FPSSE;
 			xrstor_state(init_xstate_buf, init_bv);
-			return fxrstor_checking((__force void *) buf);
+			return fxrstor_user(buf);
 		} else {
 			u64 init_bv = pcntxt_mask & ~xbv;
 			if (unlikely(init_bv))
@@ -323,9 +323,9 @@ static inline int restore_user_xstate(void __user *buf, u64 xbv, int fx_only)
 			return xrestore_user(buf, xbv);
 		}
 	} else if (use_fxsr()) {
-		return fxrstor_checking((__force void *) buf);
+		return fxrstor_user(buf);
 	} else
-		return frstor_checking((__force void *) buf);
+		return frstor_user(buf);
 }
 
 int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)