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Message-ID: <CAGXu5jKM5RZeTgTonscuLRg-+62S8UWcPbJABWqT4=7HOwb2bA@mail.gmail.com>
Date: Mon, 22 Feb 2016 12:46:28 -0800
From: Kees Cook <keescook@...omium.org>
To: PaX Team <pageexec@...email.hu>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>, Laura Abbott <labbott@...hat.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Mark Rutland <mark.rutland@....com>,
Jeremy Linton <jeremy.linton@....com>, Arnd Bergmann <arnd@...db.de>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lkdtm: add test for executing .rodata
On Thu, Feb 18, 2016 at 1:27 PM, PaX Team <pageexec@...email.hu> wrote:
> On 18 Feb 2016 at 12:34, Ard Biesheuvel wrote:
>
>> However, that does not fix the issue Kees is trying to solve, where a
>> .rodata section is emitted with the "x" bit set, which causes the
>> linker to complain:
>>
>> /tmp/cc50ffWw.s: Assembler messages:
>> /tmp/cc50ffWw.s:2: Warning: setting incorrect section attributes for
>> .rodata.text
>
> in that case why not use a top-level asm statement to set the section
> and its attributes (and compile the file with fno-toplevel-reorder)?
GCC really wants to declare the section. :(
asm(".pushsection .rodata");
static void do_nothing_rodata(void)
{
return;
}
asm(".popsection");
With -fno-toplevel-reorder, this produces:
#APP
.pushsection .rodata
#NO_APP
.section .text.unlikely
.LCOLDB42:
.text
.LHOTB42:
.p2align 4,,15
.type do_nothing_rodata, @function
do_nothing_rodata:
.LFB2756:
.loc 1 323 0
.cfi_startproc
pushq %rbp
...
So I either need to define "ret" for every architecture, define the
linker comment character for every architecture, or do some generated
file. I'll try the latter next...
-Kees
--
Kees Cook
Chrome OS & Brillo Security
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