linux-kernel - Re: [PATCH 2/4] arm64: atomics: lse: Silence intentional wrapping addition

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Message-ID: <202405020759.55CD47C@keescook>
Date: Thu, 2 May 2024 08:00:45 -0700
From: Kees Cook <keescook@...omium.org>
To: Will Deacon <will@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org,
	Jakub Kicinski <kuba@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Uros Bizjak <ubizjak@...il.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, linux-arch@...r.kernel.org, netdev@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/4] arm64: atomics: lse: Silence intentional wrapping
 addition

On Thu, May 02, 2024 at 12:21:28PM +0100, Will Deacon wrote:
> On Wed, Apr 24, 2024 at 12:17:35PM -0700, Kees Cook wrote:
> > Annotate atomic_add_return() and atomic_sub_return() to avoid signed
> > overflow instrumentation. They are expected to wrap around.
> > 
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Boqun Feng <boqun.feng@...il.com>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: linux-arm-kernel@...ts.infradead.org
> > ---
> >  arch/arm64/include/asm/atomic_lse.h | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> How come the ll/sc routines (in atomic_ll_sc.h) don't need the same
> treatment? If that's just an oversight, then maybe it's better to
> instrument the higher-level wrappers in asm/atomic.h?

Those are all written in asm, so there's no open-coded C arithmetic that
the sanitizers will notice. All is well there! :)

-- 
Kees Cook