1 files changed, 14 insertions, 2 deletions

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index d5eee851071c..08a945d7915e 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -394,8 +394,20 @@ __visible long do_fast_syscall_32(struct pt_regs *regs)
          * WARNING: We are in CONTEXT_USER and RCU isn't paying attention!
          */
         local_irq_enable();
-        if (get_user(*(u32 *)&regs->cx,
-                     (u32 __user __force *)(unsigned long)(u32)regs->sp)) {
+        if (
+#ifdef CONFIG_X86_64
+                /*
+                 * Micro-optimization: the pointer we're following is explicitly
+                 * 32 bits, so it can't be out of range.
+                 */
+                __get_user(*(u32 *)&regs->cx,
+                            (u32 __user __force *)(unsigned long)(u32)regs->sp)
+#else
+                get_user(*(u32 *)&regs->cx,
+                         (u32 __user __force *)(unsigned long)(u32)regs->sp)
+#endif
+                ) {
+
                 /* User code screwed up. */
                 local_irq_disable();
                 regs->ax = -EFAULT;