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Date: Thu, 2 May 2024 07:57:02 -0700
From: Kees Cook <keescook@chromium.org>
To: David Howells <dhowells@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>, Will Deacon <will@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Boqun Feng <boqun.feng@gmail.com>,
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	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>,
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	Andrew Morton <akpm@linux-foundation.org>,
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	David Ahern <dsahern@kernel.org>,
	Eric Dumazet <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>,
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	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
Message-ID: <202405020755.0101DBCB@keescook>
References: <20240424191740.3088894-1-keescook@chromium.org>
 <20240424191225.work.780-kees@kernel.org>
 <2100617.1714117250@warthog.procyon.org.uk>
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On Fri, Apr 26, 2024 at 08:40:50AM +0100, David Howells wrote:
> Kees Cook <keescook@chromium.org> wrote:
> 
> > -	return i + xadd(&v->counter, i);
> > +	return wrapping_add(int, i, xadd(&v->counter, i));
> 
> Ewww.  Can't you just mark the variable as wrapping in some way, either by:
> 
> 	unsigned int __cyclic counter;

Yeah, that's the plan now. Justin is currently working on the "wraps"
attribute for Clang:
https://github.com/llvm/llvm-project/pull/86618

-- 
Kees Cook