From: Andi Kleen <a...@linux.intel.com>
Add a noretpoline option boot to disable retpoline and patch
out the extra sequences. It cannot patch out the jumps
to the thunk functions generated by the compiler, but they
turn into a single indirect branch now.
Signed-off-by: Andi Kleen <a...@linux.intel.com>
Signed-off-by: David Woodhouse <d...@amazon.co.uk>
---
Documentation/admin-guide/kernel-parameters.txt | 3 +++
arch/x86/kernel/cpu/intel.c | 10 ++++++++++
2 files changed, 13 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt
b/Documentation/admin-guide/kernel-parameters.txt
index af7104a..c48db34 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2623,6 +2623,9 @@
nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
+ noretpoline [X86] Disable the retpoline kernel indirect branch
speculation
+ workarounds. System may allow data leaks with this
option.
+
nosmt [KNL,S390] Disable symmetric multithreading (SMT).
Equivalent to smt=1.
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index b1af220..4ab46f5 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -31,6 +31,16 @@
#include <asm/apic.h>
#endif
+#ifdef RETPOLINE
+static int __init noretpoline_setup(char *__unused)
+{
+ pr_info("Retpoline runtime disabled\n");
+ setup_force_cpu_cap(X86_BUG_NO_RETPOLINE);
+ return 1;
+}
+__setup("noretpoline", noretpoline_setup);
+#endif
+
/*
* Just in case our CPU detection goes bad, or you have a weird system,
* allow a way to override the automatic disabling of MPX.
--
2.7.4
