linux-kernel - Re: [PATCH v2 07/39] x86/cet: Add user control-protection fault handler

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Message-ID: <405e6b57ea18f200403f0c9044120ff92a47431a.camel@intel.com>
Date:   Mon, 3 Oct 2022 18:12:13 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
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Subject: Re: [PATCH v2 07/39] x86/cet: Add user control-protection fault
 handler

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:
> > +#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

...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.