From: Kees Cook <keescook@chromium.org>
To: Christophe Leroy <christophe.leroy@c-s.fr>,
Michael Ellerman <mpe@ellerman.id.au>
Cc: Jinbum Park <jinb.park7@gmail.com>, Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm: fix RODATA_TEST failure "rodata_test: test data was not read only"
Date: Sun, 24 Sep 2017 12:17:51 -0700 [thread overview]
Message-ID: <CAGXu5jJ54+bCcXaPK1ExsxtTDPHNn1+1gywb3TDbe-SEtt1zuQ@mail.gmail.com> (raw)
In-Reply-To: <20170921093729.1080368AC1@po15668-vm-win7.idsi0.si.c-s.fr>
On Thu, Sep 21, 2017 at 2:37 AM, Christophe Leroy
<christophe.leroy@c-s.fr> wrote:
> On powerpc, RODATA_TEST fails with message the following messages:
>
> [ 6.199505] Freeing unused kernel memory: 528K
> [ 6.203935] rodata_test: test data was not read only
>
> This is because GCC allocates it to .data section:
>
> c0695034 g O .data 00000004 rodata_test_data
Uuuh... that seems like a compiler bug. It's marked "const" -- it
should never end up in .data. I would argue that this has done exactly
what it was supposed to do, and shows that something has gone wrong.
It should always be const. Adding "static" should just change
visibility. (I'm not opposed to the static change, but it seems to
paper over a problem with the compiler...)
-Kees
>
> Since commit 056b9d8a76924 ("mm: remove rodata_test_data export,
> add pr_fmt"), rodata_test_data is used only inside rodata_test.c
> By declaring it static, it gets properly allocated into .rodata
> section instead of .data:
>
> c04df710 l O .rodata 00000004 rodata_test_data
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
> mm/rodata_test.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/rodata_test.c b/mm/rodata_test.c
> index 6bb4deb12e78..d908c8769b48 100644
> --- a/mm/rodata_test.c
> +++ b/mm/rodata_test.c
> @@ -14,7 +14,7 @@
> #include <linux/uaccess.h>
> #include <asm/sections.h>
>
> -const int rodata_test_data = 0xC3;
> +static const int rodata_test_data = 0xC3;
>
> void rodata_test(void)
> {
> --
> 2.13.3
>
--
Kees Cook
Pixel Security
next prev parent reply other threads:[~2017-09-24 19:17 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-21 9:37 [PATCH] mm: fix RODATA_TEST failure "rodata_test: test data was not read only" Christophe Leroy
2017-09-24 19:17 ` Kees Cook [this message]
2017-09-25 7:37 ` Segher Boessenkool
2017-09-25 16:01 ` David Laight
2017-09-25 19:41 ` Segher Boessenkool
2017-10-02 19:29 ` Kees Cook
2017-10-02 20:08 ` Segher Boessenkool
2017-10-02 20:27 ` Kees Cook
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