On Wed, Jul 10, 2019 at 04:22:51PM +0200, Jiri Kosina wrote: > On Wed, 10 Jul 2019, Peter Zijlstra wrote: > > > If we mark the key as RO after init, and then try and modify the key to > > link module usage sites, things might go bang as described. > > > > Thanks! > > > > > > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c > > index 27d7864e7252..5bf7a8354da2 100644 > > --- a/arch/x86/kernel/cpu/common.c > > +++ b/arch/x86/kernel/cpu/common.c > > @@ -366,7 +366,7 @@ static __always_inline void setup_umip(struct > > cpuinfo_x86 *c) > > cr4_clear_bits(X86_CR4_UMIP); > > } > > > > -DEFINE_STATIC_KEY_FALSE_RO(cr_pinning); > > +DEFINE_STATIC_KEY_FALSE(cr_pinning); > > Good catch, I guess that is going to fix it. > > At the same time though, it sort of destroys the original intent of Kees' > patch, right? The exploits will just have to call static_key_disable() > prior to calling native_write_cr4() again, and the protection is gone.
This is fixable by moving native_write_cr*() out-of-line, such that they never end up in a module.
