On Mon, 2022-10-03 at 17:01 +0300, Kirill A . Shutemov wrote:

On Thu, Sep 29, 2022 at 03:29:04PM -0700, Rick Edgecombe wrote:

quoted

+#else
+static void do_user_control_protection_fault(struct pt_regs *regs,
+                                          unsigned long
error_code)
+{
+     WARN_ONCE(1, "User-mode control protection fault with shadow
support disabled\n");

Why is this a warning, but runtime check for !X86_FEATURE_IBT and
!X86_FEATURE_SHSTK below is fatal?

It was a BUG() in the original KERNEL_IBT focused handler IIRC. There
seems to be some renewed effort to stop doing those:

https://lore.kernel.org/all/20220923113426.52871-2-david@redhat.com/T/#u (local)

...so I'll change it to a WARN for this. In the kernel specific portion
of the handler, it also does a BUG on endbranch violation. I'll leave
that one for this change.