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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	gregkh@linuxfoundation.org, pbonzini@redhat.com,
	linux-kernel@vger.kernel.org, ojeda@kernel.org,
	ndesaulniers@google.com, mingo@redhat.com, will@kernel.org,
	longman@redhat.com, boqun.feng@gmail.com, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	bristot@redhat.com, vschneid@redhat.com, paulmck@kernel.org,
	frederic@kernel.org, quic_neeraju@quicinc.com,
	joel@joelfernandes.org, josh@joshtriplett.org,
	mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
	rcu@vger.kernel.org, tj@kernel.org, tglx@linutronix.de,
	linux-toolchains@vger.kernel.org
Subject: Re: [PATCH v2 0/2] Lock and Pointer guards
Date: Tue, 6 Jun 2023 08:45:49 -0700	[thread overview]
Message-ID: <CAHk-=wh=vs298o0gewFH725pQAYQ57CAQzj05FOx_VZubZ3jiA@mail.gmail.com> (raw)
In-Reply-To: <202306060829.C2FD998CF@keescook>

On Tue, Jun 6, 2023 at 8:31 AM Kees Cook <keescook@chromium.org> wrote:
>
> nit: Linus's example was "(void *)8" (instead of 1) because we've had
> issues in the past with alignment warnings on archs that are sensitive
> to it. (e.g. see the __is_constexpr() macro which is doing NULL/!NULL
> comparisons.)

Note that I don't think we ever saw such a warning, it was just a
theoretical observation that depending on type, the compiler might
warn about known mis-aligned pointer bits.

So I'm not sure the 1-vs-8 actually matters. We do other things that
assume that low bits in a pointer are retained and valid, even if in
theory the C type system might have issues with it.

But maybe I mis-remember - if you did get an actual warning, maybe we
should document that warning just to keep the memory alive.

            Linus

  reply	other threads:[~2023-06-06 15:46 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-26 20:52 [PATCH v2 0/2] Lock and Pointer guards Peter Zijlstra
2023-05-26 20:52 ` [PATCH v2 1/2] locking: Introduce __cleanup__ based guards Peter Zijlstra
2023-05-26 21:24   ` Peter Zijlstra
2023-05-26 21:54     ` Linus Torvalds
2023-05-27  8:57       ` Peter Zijlstra
2023-05-26 20:52 ` [PATCH v2 2/2] sched: Use fancy new guards Peter Zijlstra
2023-05-27 17:21 ` [PATCH v2 0/2] Lock and Pointer guards Mathieu Desnoyers
2023-05-27 19:18 ` Linus Torvalds
2023-05-29 12:09   ` Paolo Bonzini
2023-05-29 19:04     ` Linus Torvalds
2023-05-29 21:27       ` Ian Lance Taylor
2023-05-30  0:06         ` Linus Torvalds
2023-05-30  9:23   ` Peter Zijlstra
2023-05-30  9:34     ` Peter Zijlstra
2023-05-30 13:58     ` Valentin Schneider
2023-06-06  9:42     ` Peter Zijlstra
2023-06-06 13:17       ` Linus Torvalds
2023-06-06 13:40         ` Peter Zijlstra
2023-06-06 14:50           ` Linus Torvalds
2023-06-06 16:06             ` Kees Cook
2023-06-06 18:08             ` Peter Zijlstra
2023-06-06 23:22               ` Linus Torvalds
2023-06-07  9:41                 ` Peter Zijlstra
2023-06-08  8:52                   ` Peter Zijlstra
2023-06-08  9:04                     ` Greg KH
2023-06-08 15:45                     ` Linus Torvalds
2023-06-08 16:47                       ` Kees Cook
2023-06-08 16:59                         ` Linus Torvalds
2023-06-08 17:20                         ` Nick Desaulniers
2023-06-08 18:51                           ` Peter Zijlstra
2023-06-08 20:14                             ` Nick Desaulniers
2023-06-09 10:20                               ` Paolo Bonzini
2023-06-08 20:06                       ` Peter Zijlstra
2023-06-09  2:25                         ` Linus Torvalds
2023-06-09  8:14                           ` Peter Zijlstra
2023-06-09 21:18                           ` Kees Cook
2023-06-09  8:27                       ` Rasmus Villemoes
2023-06-06 15:31       ` Kees Cook
2023-06-06 15:45         ` Linus Torvalds [this message]
2023-06-06 16:08           ` Kees Cook
2023-06-08 16:25           ` David Laight
2023-05-30  9:26   ` Peter Zijlstra

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