linux-hardening - Re: [RFC PATCH 3/7] kcfi: Add core Kernel Control Flow Integrity infrastructure

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Message-ID: <20250821091220.GM4067720@noisy.programming.kicks-ass.net>
Date: Thu, 21 Aug 2025 11:12:20 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Andrew Pinski <andrew.pinski@....qualcomm.com>
Cc: Kees Cook <kees@...nel.org>, Qing Zhao <qing.zhao@...cle.com>,
	gcc-patches@....gnu.org, Joseph Myers <josmyers@...hat.com>,
	Richard Biener <rguenther@...e.de>, Jan Hubicka <hubicka@....cz>,
	Richard Earnshaw <richard.earnshaw@....com>,
	Richard Sandiford <richard.sandiford@....com>,
	Marcus Shawcroft <marcus.shawcroft@....com>,
	Kyrylo Tkachov <kyrylo.tkachov@....com>,
	Kito Cheng <kito.cheng@...il.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Andrew Waterman <andrew@...ive.com>,
	Jim Wilson <jim.wilson.gcc@...il.com>,
	Dan Li <ashimida.1990@...il.com>, linux-hardening@...r.kernel.org
Subject: Re: [RFC PATCH 3/7] kcfi: Add core Kernel Control Flow Integrity
 infrastructure

On Thu, Aug 21, 2025 at 01:16:56AM -0700, Andrew Pinski wrote:

> > +/* Compute KCFI type ID for a function declaration or function type
> > (internal) */
> > +static uint32_t
> > +compute_kcfi_type_id (tree fntype_or_fndecl)
> > +{
> > +  if (!fntype_or_fndecl)
> > +    return 0;
> > +
> > +  const char *canonical_name = mangle_function_type (fntype_or_fndecl);
> > +  uint32_t base_type_id = kcfi_hash_string (canonical_name);
> >
> 
> Now I am curious why this needs to be a mangled function name? Since the
> function in C the symbol is just its name.
> Is there documentation that says the hash needs to be based on all of the
> function arguments types?

The whole point of kCFI is to limit the targets of indirect calls to
functions of the same signature. The actual function name is immaterial.