Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...

[sfrench/cifs-2.6.git] / arch / x86 / entry / entry_64.S

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 4f8e1d35a97ca7071a11f33f07e2b87c2eac7acf..aa15b4c0e3d17dd64f513ce6a1915cdd24829016 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -491,6 +491,17 @@ ENTRY(__switch_to_asm)
        movq    %rbx, PER_CPU_VAR(irq_stack_union)+stack_canary_offset
 #endif
 
+#ifdef CONFIG_RETPOLINE
+       /*
+        * When switching from a shallower to a deeper call stack
+        * the RSB may either underflow or use entries populated
+        * with userspace addresses. On CPUs where those concerns
+        * exist, overwrite the RSB with entries which capture
+        * speculative execution to prevent attack.
+        */
+       FILL_RETURN_BUFFER %r12, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
+#endif
+
        /* restore callee-saved registers */
        popq    %r15
        popq    %r14