From: Kees Cook <keescook@chromium.org>
To: Linus Torvalds <torvalds@linux-foundation.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 09:08:32 -0700 [thread overview]
Message-ID: <202306060907.D335A9F@keescook> (raw)
In-Reply-To: <CAHk-=wh=vs298o0gewFH725pQAYQ57CAQzj05FOx_VZubZ3jiA@mail.gmail.com>
On Tue, Jun 06, 2023 at 08:45:49AM -0700, Linus Torvalds wrote:
> 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.
I've never seen a warning, but since this came up in the dissection of
the __is_constexpr() behavior, it's been burned into my mind. ;)
--
Kees Cook
next prev parent reply other threads:[~2023-06-06 16:08 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
2023-06-06 16:08 ` Kees Cook [this message]
2023-06-08 16:25 ` David Laight
2023-05-30 9:26 ` Peter Zijlstra
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