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Date:   Sat, 12 Nov 2022 10:47:58 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "H. Peter Anvin" <hpa@zytor.com>
Cc:     "Li, Xin3" <xin3.li@intel.com>,
        "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>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "Tian, Kevin" <kevin.tian@intel.com>
Subject: Re: [RESEND PATCH 2/6] x86/traps: add a system interrupt table for
 system interrupt dispatch
Message-ID: <Y29rzovA90RWZjo1@hirez.programming.kicks-ass.net>
References: <20221110061545.1531-1-xin3.li@intel.com>
 <20221110061545.1531-3-xin3.li@intel.com>
 <Y2y8obdYDXo9vlH/@hirez.programming.kicks-ass.net>
 <BN6PR1101MB21619E2092AFF048422C6311A8019@BN6PR1101MB2161.namprd11.prod.outlook.com>
 <EA13BAB1-FD67-4145-9325-5705FEE6915A@zytor.com>
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In-Reply-To: <EA13BAB1-FD67-4145-9325-5705FEE6915A@zytor.com>
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On Fri, Nov 11, 2022 at 02:07:05PM -0800, H. Peter Anvin wrote:
> On November 10, 2022 11:55:22 AM PST, "Li, Xin3" <xin3.li@intel.com> wrote:
> >> > Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> >> > Signed-off-by: Xin Li <xin3.li@intel.com>
> >> 
> >> This is not a valid SOB, it would suggest hpa is the author, but he's not in in
> >> From.
> >
> >HPA wrote the initial dispatch code for FRED, and I worked with him to
> >refactor it for KVM/VMX NMI/IRQ dispatch.  So use SOB from both.  No?
> >
> >> > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index
> >> > 178015a820f0..95dd917ef9ad 100644
> >> > --- a/arch/x86/kernel/traps.c
> >> > +++ b/arch/x86/kernel/traps.c
> >> > @@ -1444,6 +1444,61 @@ DEFINE_IDTENTRY_SW(iret_error)  }  #endif
> >> >
> >> > +#define SYSV(x,y) [(x) - FIRST_SYSTEM_VECTOR] =
> >> > +(system_interrupt_handler)y
> >> > +
> >> > +#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.
> >
> 
> It doesn't break CFI because the arguments passed is always a strict
> superset of the ones expected and they are free enough that they are
> always passed in registers.

It does break CFI because the signature hash doesn't match and you'll
trigger an explicit UD2.