linux-kernel - Re: [PATCH v5 13/36] bit_spinlock: Support Clang's context analysis

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <CANpmjNN6QrxwUUkpAopTfxLwUqGfB53J96dwOWHNcoYrOrEocQ@mail.gmail.com>
Date: Fri, 19 Dec 2025 22:09:23 +0100
From: Marco Elver <elver@...gle.com>
To: Bart Van Assche <bvanassche@....org>
Cc: Peter Zijlstra <peterz@...radead.org>, Boqun Feng <boqun.feng@...il.com>, 
	Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Luc Van Oostenryck <luc.vanoostenryck@...il.com>, 
	Chris Li <sparse@...isli.org>, "Paul E. McKenney" <paulmck@...nel.org>, 
	Alexander Potapenko <glider@...gle.com>, Arnd Bergmann <arnd@...db.de>, Christoph Hellwig <hch@....de>, 
	Dmitry Vyukov <dvyukov@...gle.com>, Eric Dumazet <edumazet@...gle.com>, 
	Frederic Weisbecker <frederic@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Herbert Xu <herbert@...dor.apana.org.au>, Ian Rogers <irogers@...gle.com>, 
	Jann Horn <jannh@...gle.com>, Joel Fernandes <joelagnelf@...dia.com>, 
	Johannes Berg <johannes.berg@...el.com>, Jonathan Corbet <corbet@....net>, 
	Josh Triplett <josh@...htriplett.org>, Justin Stitt <justinstitt@...gle.com>, 
	Kees Cook <kees@...nel.org>, Kentaro Takeda <takedakn@...data.co.jp>, 
	Lukas Bulwahn <lukas.bulwahn@...il.com>, Mark Rutland <mark.rutland@....com>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Neeraj Upadhyay <neeraj.upadhyay@...nel.org>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Thomas Gleixner <tglx@...utronix.de>, 
	Thomas Graf <tgraf@...g.ch>, Uladzislau Rezki <urezki@...il.com>, Waiman Long <longman@...hat.com>, 
	kasan-dev@...glegroups.com, linux-crypto@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	linux-security-module@...r.kernel.org, linux-sparse@...r.kernel.org, 
	linux-wireless@...r.kernel.org, llvm@...ts.linux.dev, rcu@...r.kernel.org
Subject: Re: [PATCH v5 13/36] bit_spinlock: Support Clang's context analysis

On Fri, 19 Dec 2025 at 21:48, 'Bart Van Assche' via kasan-dev
<kasan-dev@...glegroups.com> wrote:
>
> On 12/19/25 7:40 AM, Marco Elver wrote:
> > +/*
> > + * For static context analysis, we need a unique token for each possible bit
> > + * that can be used as a bit_spinlock. The easiest way to do that is to create a
> > + * fake context that we can cast to with the __bitlock(bitnum, addr) macro
> > + * below, which will give us unique instances for each (bit, addr) pair that the
> > + * static analysis can use.
> > + */
> > +context_lock_struct(__context_bitlock) { };
> > +#define __bitlock(bitnum, addr) (struct __context_bitlock *)(bitnum + (addr))
>
> Will this cause static analyzers to complain about out-of-bounds
> accesses for (bitnum + (addr)), which is equivalent to &(addr)[bitnum]?

Only if they decide to interpret never-executed code (i think the
kernel has various dead code that's optimized out that might trigger
static analyzers if they analyzed it).
But this could probably be improved by using a different idiom, and
using an empty inline function that takes bitnum, addr as args, and
Clang simply takes the call to that function as the context lock
identity.