From: Andi Kleen <[email protected]> Add a noretpoline option boot to disable retpoline and patch out the extra sequences. It cannot patch out the jumps to the thunk functions from code generated by the compiler, but those thunks turn into a single indirect branch now.
Signed-off-by: Andi Kleen <[email protected]> Signed-off-by: David Woodhouse <[email protected]> Acked-By: Arjan van de Ven <[email protected]> --- Documentation/admin-guide/kernel-parameters.txt | 3 +++ arch/x86/kernel/cpu/intel.c | 11 +++++++++++ 2 files changed, 14 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 9059917..d443141 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2596,6 +2596,9 @@ 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 b720dac..35e123e 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -31,6 +31,17 @@ #include <asm/apic.h> #endif +#ifdef RETPOLINE +static int __init noretpoline_setup(char *__unused) +{ + pr_info("Retpoline runtime disabled\n"); + setup_clear_cpu_cap(X86_FEATURE_RETPOLINE); + setup_clear_cpu_cap(X86_FEATURE_RETPOLINE_AMD); + 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
