linux-kernel - Re: [PATCH v2 00/13] objtool: Detect and warn about indirect calls in _

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Message-ID: <20250501103038.GB4356@noisy.programming.kicks-ass.net>
Date: Thu, 1 May 2025 12:30:38 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org, kys@...rosoft.com, haiyangz@...rosoft.com,
	wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de,
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
	seanjc@...gle.com, pbonzini@...hat.com, ardb@...nel.org,
	kees@...nel.org, Arnd Bergmann <arnd@...db.de>,
	gregkh@...uxfoundation.org, jpoimboe@...nel.org,
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, linux-efi@...r.kernel.org,
	samitolvanen@...gle.com, ojeda@...nel.org, xin@...or.com
Subject: Re: [PATCH v2 00/13] objtool: Detect and warn about indirect calls
 in __nocfi functions

On Wed, Apr 30, 2025 at 09:06:00PM +0200, Peter Zijlstra wrote:
> On Wed, Apr 30, 2025 at 07:24:15AM -0700, H. Peter Anvin wrote:
> 
> > >KVM has another; the VMX interrupt injection stuff calls the IDT handler
> > >directly.  Is there an alternative? Can we keep a table of Linux functions
> > >slighly higher up the call stack (asm_\cfunc ?) and add CFI to those?
> 
> > We do have a table of handlers higher up in the stack in the form of
> > the dispatch tables for FRED. They don't in general even need the
> > assembly entry stubs, either.
> 
> Oh, right. I'll go have a look at those.

Right, so perhaps the easiest way around this is to setup the FRED entry
tables unconditionally, have VMX mandate CONFIG_FRED and then have it
always use the FRED entry points.

Let me see how ugly that gets.