linux-kernel - Re: [PATCH] lkdtm: add test for executing .rodata

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Message-ID: <56C59DC5.19217.28FA99@pageexec.freemail.hu>
Date:	Thu, 18 Feb 2016 11:32:37 +0100
From:	"PaX Team" <pageexec@...email.hu>
To:	Laura Abbott <labbott@...hat.com>,
	Kees Cook <keescook@...omium.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Rutland <mark.rutland@....com>,
	Jeremy Linton <jeremy.linton@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	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 17 Feb 2016 at 12:29, Kees Cook wrote:

> >> +static void __attribute__((__section__(".rodata,\"a\",@progbits#")))
> >> +do_nothing_rodata(void)
> >> +{
> >> +       return;
> >> +}
> >> +
> >
> >
> >>
> >
> > This doesn't cross compile for me on arm64 with two different toolchains
> >
> > CC drivers/misc/lkdtm.o
> > /tmp/ccHzIWIx.s: Assembler messages:
> > /tmp/ccHzIWIx.s:21: Error: junk at end of line, first unrecognized character
> > is `#'
> > /tmp/ccHzIWIx.s: Error: unaligned opcodes detected in executable segment
> > scripts/Makefile.build:258: recipe for target 'drivers/misc/lkdtm.o' failed
> > make[2]: *** [drivers/misc/lkdtm.o] Error 1
> > scripts/Makefile.build:407: recipe for target 'drivers/misc' failed
> > make[1]: *** [drivers/misc] Error 2
> > Makefile:950: recipe for target 'drivers' failed
> > make: *** [drivers] Error 2
> >
> > I don't know the assembler well enough to give any insight.
> 
> Hm, bummer. I was trying to get fancy with the function forced into
> .rodata by trying to force the bits. Looks like "#" is not seen as a
> comment character by the toolchain you're using.
> 
> Anyone else successfully done tricks like this?

wouldn't it be a better and more generic/reusable approach to

#define __ro_text __attribute__((__section__(".rodata.text")))

and move this function there by the linker script similar to how it's done
for other code that goes into special sections?