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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250822082420.GB1386988@noisy.programming.kicks-ass.net>
Date: Fri, 22 Aug 2025 10:24:20 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Andrew Pinski <pinskia@...il.com>
Cc: Andrew Pinski <andrew.pinski@....qualcomm.com>,
	Kees Cook <kees@...nel.org>, Qing Zhao <qing.zhao@...cle.com>,
	GCC Patches <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 Fri, Aug 22, 2025 at 09:51:15AM +0200, Peter Zijlstra wrote:
> On Thu, Aug 21, 2025 at 02:22:30AM -0700, Andrew Pinski wrote:
> > On Thu, Aug 21, 2025, 2:13 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > 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.
> > >
> > 
> > 
> > So then just hash the function argument types. It only needs to be
> > consistent for the objects that are compiled together right?
> 
> Function argument and return; but yes that could be done. Ideally the
> kCFI implementation would be compatible between compilers. Specifically
> rust is based on llvm and therefore generates kCFI that is compatible
> with clang. Being able to mix GCC and rust code (as the kernel does)
> would be nice.

FWIW, Kees, for this to actually work, we need this
CFI_ICALL_NORMALIZE_INTEGERS thing supported. Rust gets really upset
about LP64's whole 'long' vs 'long long' trainwreck :/

That is the -fsanitize-cfi-icall-experimental-normalize-integers
argument for clang (omg so long).