From: Kees Cook <keescook@chromium.org>
To: Joe Perches <joe@perches.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Dan Carpenter <error27@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
zhanglin <zhang.lin16@zte.com.cn>
Subject: Re: [PATCH] kernel: sys.c: Avoid copying possible padding bytes in copy_to_user
Date: Mon, 28 Oct 2019 11:58:34 -0700 [thread overview]
Message-ID: <201910281153.7B6F79DBD@keescook> (raw)
In-Reply-To: <92212e57d45f4410be654183f5dcb1e98d636ef2.camel@perches.com>
On Sun, Oct 27, 2019 at 03:47:21PM -0700, Joe Perches wrote:
> I think yes as at least it makes it consistent.
>
> From the link above, as I understand the __user
> gcc extension here
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c61f13eaa1ee17728c41370100d2d45c254ce76f
>
> gcc does not clear padding from initialized structs
> marked with __user.
It seems to depend on how complete the initialization is and/or how
large the structure is. AFAICT, based on the tests I wrote[1], if
CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF (or ..._ALL) are used, even padding
will get initialized as long as things are in memory. (And the same is
true with Clang under CONFIG_INIT_STACK_ALL.)
> Though that doesn't force the compiler to not
> perform the possible register optimization shown
> in the first document above.
Right. This is the only case where things aren't clear. I haven't been
able to build a test where "store in registers" behavior is tripped.
-Kees
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/test_stackinit.c
--
Kees Cook
next prev parent reply other threads:[~2019-10-28 18:58 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-26 19:46 [PATCH] kernel: sys.c: Avoid copying possible padding bytes in copy_to_user Joe Perches
2019-10-27 5:47 ` Julia Lawall
2019-10-27 22:47 ` Joe Perches
2019-10-28 7:30 ` Dan Carpenter
2019-10-28 18:58 ` Kees Cook [this message]
2019-10-28 7:18 ` Dan Carpenter
2019-10-28 8:08 ` Joe Perches
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=201910281153.7B6F79DBD@keescook \
--to=keescook@chromium.org \
--cc=akpm@linux-foundation.org \
--cc=error27@gmail.com \
--cc=joe@perches.com \
--cc=julia.lawall@lip6.fr \
--cc=linux-kernel@vger.kernel.org \
--cc=tglx@linutronix.de \
--cc=zhang.lin16@zte.com.cn \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox