linux-kernel - Re: [PATCH v4 2/2] extable: verify address is read-only

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Message-ID: <CAGXu5jKFPwDTaRq8eiszOoqdm-nQD13UrF_bj+m6FWWCzEnO9g@mail.gmail.com>
Date:   Mon, 27 Mar 2017 11:42:57 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Eddie Kovsky <ewk@...ovsky.org>
Cc:     kbuild-all@...org, kbuild test robot <lkp@...el.com>,
        Jessica Yu <jeyu@...hat.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v4 2/2] extable: verify address is read-only

On Mon, Mar 27, 2017 at 1:43 AM, kbuild test robot <lkp@...el.com> wrote:
> Hi Eddie,
>
> [auto build test ERROR on next-20170323]
> [cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc4]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>
> url:    https://github.com/0day-ci/linux/commits/Eddie-Kovsky/module-verify-address-is-read-only/20170327-142922
> config: blackfin-BF561-EZKIT-SMP_defconfig (attached as .config)
> compiler: bfin-uclinux-gcc (GCC) 6.2.0
> reproduce:
>         wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=blackfin
>
> All errors (new ones prefixed by >>):
>
>    kernel/built-in.o: In function `core_kernel_rodata':
>>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'

Hm, I'm confused about this. blackfin includes
include/asm-generic-vmlinux.lds.h and uses the RO_DATA macro (which
resolves to RO_DATA_SECTION to RO_AFTER_INIT_DATA which defines
__[start|end]_data_ro_after_init.

Also, it seems that commit d7c19b066dcf4bd19c4385e8065558d4e74f9e73
("mm: kmemleak: scan .data.ro_after_init") added a potentially
redundant section name (s390 already calls this
__[start|end]_ro_after_init). I'd like to get this cleaned up, since
having multiple names for the same thing is confusing:

diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S
index 000e6e91f6a0..3667d20e997f 100644
--- a/arch/s390/kernel/vmlinux.lds.S
+++ b/arch/s390/kernel/vmlinux.lds.S
@@ -62,9 +62,11 @@ SECTIONS

        . = ALIGN(PAGE_SIZE);
        __start_ro_after_init = .;
+       __start_data_ro_after_init = .;
        .data..ro_after_init : {
                 *(.data..ro_after_init)
        }
+       __end_data_ro_after_init = .;
        EXCEPTION_TABLE(16)
        . = ALIGN(PAGE_SIZE);
        __end_ro_after_init = .;

And it seems that this hunk is wrong (__end_ro_after_init includes
s390's exception table, etc). I think we should remove the
..._data_... name and use s390's name.

I'll send an adjustment patch, but we'll still need to deal with blackfin.

-Kees

>
> vim +169 kernel/extable.c
>
>    163  int core_kernel_rodata(unsigned long addr)
>    164  {
>    165          if (addr >= (unsigned long)__start_rodata &&
>    166              addr < (unsigned long)__end_rodata)
>    167                  return 1;
>    168
>  > 169          if (addr >= (unsigned long)__start_data_ro_after_init &&
>    170              addr < (unsigned long)__end_data_ro_after_init)
>    171                  return 1;
>    172
>
> ---
> 0-DAY kernel test infrastructure                Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation



-- 
Kees Cook
Pixel Security