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Date:   Thu, 10 Nov 2022 17:08:11 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     "Li, Xin3" <xin3.li@intel.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        "llvm@lists.linux.dev" <llvm@lists.linux.dev>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Kees Cook <keescook@chromium.org>
Subject: Re: [RESEND PATCH 2/6] x86/traps: add a system interrupt table for
 system interrupt dispatch
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On Thu, Nov 10, 2022 at 11:00:51PM +0000, Li, Xin3 wrote:
> > > > > > +#pragma GCC diagnostic push
> > > > > > +#pragma GCC diagnostic ignored "-Wcast-function-type"
> > > > >
> > > > > How does this not break CFI ?
> > > >
> > > > I wasn't aware of it, will check.
> > >
> > > CFI needs $(cc-option,-fsanitize=kcfi), which, reported on LWN on Jun,
> > > 2002, had not yet landed in the LLVM mainline (I'm using GCC).  So
> > > looks we are replying on people keeping an eye on it to make sure it's not
> > broken?
> > 
> > Well, the entire point of the warning that you are disabling here is to catch
> > potential CFI failures at compile time, rather than run time :)
> 
> Oh, of course I didn't intend to be opposed to CFI.

Oh, I apologize if I gave the impression that you were, I did not mean
to put words in your mouth! I was just giving additional context as to
why we have that warning enable and how we use it to help catch
potential run time failures at compile time, which does not require
running CFI to keep CFI happy.

Cheers,
Nathan

> > Clang also has -Wcast-function-type-strict, which Gustavo and Kees are working
> > on getting enabled, so that even more CFI failures can be caught at compile
> > time.
> > 
> > https://github.com/ClangBuiltLinux/linux/issues/1724
> > https://lore.kernel.org/all/?q=-Wcast-function-type-strict
> > 
> > Cheers,
> > Nathan