Re: [PATCH v2 04/39] x86/cpufeatures: Enable CET CR4 bit for shadow stack

On Fri, 2022-10-14 at 19:12 +0200, Borislav Petkov wrote:

On Thu, Sep 29, 2022 at 03:29:01PM -0700, Rick Edgecombe wrote:

quoted

  static __always_inline void setup_cet(struct cpuinfo_x86 *c)
  {
-     u64 msr = CET_ENDBR_EN;
+     bool kernel_ibt = HAS_KERNEL_IBT &&
cpu_feature_enabled(X86_FEATURE_IBT);

So I'd love it if we can get rid of that HAS_KERNEL_IBT thing and use
the usual ifdeffery with Kconfig symbols. I wouldn't like for yet
another HAS_XXX feature checking method to proliferate as this is the
only one:

Andrew Cooper has suggested to create some software cpu features to
differentiate user/supervisor CET feature use. It could replace
HAS_KERNEL_IBT. Any objections to that versus Kconfig symbols?

[snip]

cpu_feature_enabled(X86_FEATURE_IBT))

quoted

  __noendbr void cet_disable(void)
  {
-     if (cpu_feature_enabled(X86_FEATURE_IBT))
-             wrmsrl(MSR_IA32_S_CET, 0);
+     if (!(cpu_feature_enabled(X86_FEATURE_IBT) ||
+           cpu_feature_enabled(X86_FEATURE_SHSTK)))
+             return;
+
+     wrmsrl(MSR_IA32_S_CET, 0);
+     wrmsrl(MSR_IA32_U_CET, 0);
  }
  
+

Stray newline.

Oops, will clean that up. Thanks.