> On Jul 10, 2019, at 7:22 AM, Jiri Kosina <ji...@kernel.org> 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.
Even with DEFINE_STATIC_KEY_FALSE_RO(), I presume you can just call set_memory_rw(), make the page that holds the key writable, and then call static_key_disable(), followed by a call to native_write_cr4().
