Re: [PATCH 1/4] locking/atomic/x86: Silence intentional wrapping addition

From: Kees Cook <keescook@chromium.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Will Deacon <will@kernel.org>, Boqun Feng <boqun.feng@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	"David S. Miller" <davem@davemloft.net>,
	David Ahern <dsahern@kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	Paolo Abeni <pabeni@redhat.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Uros Bizjak <ubizjak@gmail.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
	netdev@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH 1/4] locking/atomic/x86: Silence intentional wrapping addition
Date: Wed, 24 Apr 2024 15:45:07 -0700	[thread overview]
Message-ID: <202404241542.6AFC3042C1@keescook> (raw)
In-Reply-To: <20240424224141.GX40213@noisy.programming.kicks-ass.net>

On Thu, Apr 25, 2024 at 12:41:41AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 24, 2024 at 12:17:34PM -0700, Kees Cook wrote:
> 
> > @@ -82,7 +83,7 @@ static __always_inline bool arch_atomic_add_negative(int i, atomic_t *v)
> >  
> >  static __always_inline int arch_atomic_add_return(int i, atomic_t *v)
> >  {
> > -	return i + xadd(&v->counter, i);
> > +	return wrapping_add(int, i, xadd(&v->counter, i));
> >  }
> >  #define arch_atomic_add_return arch_atomic_add_return
> 
> this is going to get old *real* quick :-/
> 
> This must be the ugliest possible way to annotate all this, and then
> litter the kernel with all this... urgh.

I'm expecting to have explicit wrapping type annotations soon[1], but for
the atomics, it's kind of a wash on how intrusive the annotations get. I
had originally wanted to mark the function (as I did in other cases)
rather than using the helper, but Mark preferred it this way. I'm happy
to do whatever! :)

-Kees

[1] https://github.com/llvm/llvm-project/pull/86618

-- 
Kees Cook