From: Segher Boessenkool <segher@kernel.crashing.org>
To: Marco Elver <elver@google.com>
Cc: Kees Cook <keescook@chromium.org>,
Thomas Gleixner <tglx@linutronix.de>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Elena Reshetova <elena.reshetova@intel.com>,
Mark Rutland <mark.rutland@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Alexander Potapenko <glider@google.com>,
Jann Horn <jannh@google.com>,
Peter Collingbourne <pcc@google.com>,
kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
llvm@lists.linux.dev, linux-toolchains@vger.kernel.org
Subject: Re: randomize_kstack: To init or not to init?
Date: Thu, 9 Dec 2021 14:16:16 -0600 [thread overview]
Message-ID: <20211209201616.GU614@gate.crashing.org> (raw)
In-Reply-To: <YbHTKUjEejZCLyhX@elver.google.com>
On Thu, Dec 09, 2021 at 10:58:01AM +0100, Marco Elver wrote:
> Clang supports CONFIG_INIT_STACK_ALL_ZERO, which appears to be the
> default since dcb7c0b9461c2, which is why this came on my radar. And
> Clang also performs auto-init of allocas when auto-init is on
> (https://reviews.llvm.org/D60548), with no way to skip. As far as I'm
> aware, GCC 12's upcoming -ftrivial-auto-var-init= doesn't yet auto-init
> allocas.
The space allocated by alloca is not an automatic variable, so of course
it is not affected by this compiler flag. And it should not, this flag
is explicitly for *small fixed-size* stack variables (initialising
others can be much too expensive).
> C. Introduce a new __builtin_alloca_uninitialized().
That is completely backwards. That is the normal behaviour of alloca
already. Also you can get __builtin_alloca inserted by the compiler
(for a variable length array for example), and you typically do not want
those initialised either, for the same reasons.
Segher
next prev parent reply other threads:[~2021-12-09 20:23 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-09 9:58 randomize_kstack: To init or not to init? Marco Elver
2021-12-09 10:27 ` Peter Zijlstra
2021-12-09 12:58 ` Marco Elver
2021-12-09 20:16 ` Segher Boessenkool [this message]
2021-12-09 20:33 ` Marco Elver
2021-12-20 7:00 ` Marco Elver
2021-12-09 20:48 ` Kees Cook
2021-12-09 20:54 ` Marco Elver
2021-12-09 21:11 ` Alexander Potapenko
2021-12-10 0:01 ` Segher Boessenkool
2021-12-10 0:01 ` Segher Boessenkool
2021-12-09 21:14 ` Kees Cook
2021-12-09 21:16 ` Jann Horn
2021-12-09 21:40 ` Marco Elver
2021-12-11 17:01 ` David Laight
2021-12-11 20:20 ` Segher Boessenkool
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20211209201616.GU614@gate.crashing.org \
--to=segher@kernel.crashing.org \
--cc=elena.reshetova@intel.com \
--cc=elver@google.com \
--cc=glider@google.com \
--cc=jannh@google.com \
--cc=kasan-dev@googlegroups.com \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-toolchains@vger.kernel.org \
--cc=llvm@lists.linux.dev \
--cc=mark.rutland@arm.com \
--cc=nathan@kernel.org \
--cc=ndesaulniers@google.com \
--cc=pcc@google.com \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.