linux-kernel - Re: [PATCH] lkdtm: Fix content of section containing lkdtm_rodata_do

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Message-ID: <202110081415.E36B67FA@keescook>
Date:   Fri, 8 Oct 2021 14:16:19 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH] lkdtm: Fix content of section containing
 lkdtm_rodata_do_nothing()

On Fri, Oct 08, 2021 at 11:09:47AM -0700, Nick Desaulniers wrote:
> On Fri, Oct 8, 2021 at 9:59 AM Christophe Leroy
> <christophe.leroy@...roup.eu> wrote:
> >
> > On a kernel without CONFIG_STRICT_KERNEL_RWX, running EXEC_RODATA
> > test leads to "Illegal instruction" failure.
> >
> > Looking at the content of rodata_objcopy.o, we see that the
> > function content zeroes only:
> >
> >         Disassembly of section .rodata:
> >
> >         0000000000000000 <.lkdtm_rodata_do_nothing>:
> >            0:   00 00 00 00     .long 0x0
> >
> > Add the contents flag in order to keep the content of the section
> > while renaming it.
> >
> >         Disassembly of section .rodata:
> >
> >         0000000000000000 <.lkdtm_rodata_do_nothing>:
> >            0:   4e 80 00 20     blr
> >
> > Fixes: e9e08a07385e ("lkdtm: support llvm-objcopy")
> 
> Thanks for the patch; sorry I broke this.
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

Hah! Whoops; sorry I don't have an inverted version of this test! I
should have caught this when it broke. :|

-Kees

-- 
Kees Cook