linux-kernel - Re: [BUG v5.2-rc1] ARM build broken

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Date:   Mon, 20 May 2019 21:21:54 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Kees Cook <keescook@...omium.org>,
        "H. Nikolaus Schaller" <hns@...delico.com>
CC:     lkml <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: [BUG v5.2-rc1] ARM build broken

On 21/05/19 6:54 AM, Kees Cook wrote:
> [Adding Chris and Ard, who might have more compiler versions that me...]

Late to the thread but ...

> 
> On Mon, May 20, 2019 at 07:08:39PM +0200, H. Nikolaus Schaller wrote:
>>> Am 20.05.2019 um 17:59 schrieb Kees Cook <keescook@...omium.org>:
>>>
>>> On Mon, May 20, 2019 at 05:15:02PM +0200, H. Nikolaus Schaller wrote:
>>>> Hi,
>>>> it seems as if ARM build is broken since ARM now hard enables CONFIG_HAVE_GCC_PLUGINS
>>>> which indirectly enables CONFIG_GCC_PLUGIN_ARM_SSP_PER_TASK. Compiling this breaks
>>>> on my system (Darwin build host) due to conflicts in system headers and Linux headers.
>>>>
>>>> So how can I turn off all these GCC_PLUGINS?
>>>>
>>>> The offending patch seems to be
>>>>
>>>> 	security: Create "kernel hardening" config area
>>>>
>>>> especially the new "default y" for GCC_PLUGINS. After removing that line from
>>>> scripts/gcc-plugins/Kconfig makes my compile succeed.
>>>
>>> The intention is to enable it _if_ the plugins are available as part of
>>> the build environment. The "default y" on GCC_PLUGINS is mediated by:
>>>         depends on HAVE_GCC_PLUGINS
>>
>> HAVE_GCC_PLUGINS has the following description:
>>
>> 	An arch should select this symbol if it supports building with
>>            GCC plugins.
>>
>> So an ARCH (ARM) selects it unconditionally of the build environment.
>>
>>>         depends on PLUGIN_HOSTCC != ""
>>
>> Well, we have it set to "g++" for ages and it was not a problem.
>> So both conditions are true.
> 
> PLUGIN_HOSTCC should have passed the scripts/gcc-plugin.sh test, so
> that's correct. And the result (CONFIG_GCC_PLUGINS) is correct: it
> doesn't enable or disable anything itself.
> 
> What you want is to disable CONFIG_STACKPROTECTOR_PER_TASK, which
> is the knob for the feature:
> 
> config STACKPROTECTOR_PER_TASK
>          bool "Use a unique stack canary value for each task"
>          depends on GCC_PLUGINS && STACKPROTECTOR && SMP && !XIP_DEFLATED_DATA
>          select GCC_PLUGIN_ARM_SSP_PER_TASK
>          default y
> 
>> Build error:
>>
>>   HOSTCXX -fPIC scripts/gcc-plugins/arm_ssp_per_task_plugin.o - due to: scripts/gcc-plugins/gcc-common.h
>> In file included from scripts/gcc-plugins/arm_ssp_per_task_plugin.c:3:0:
>> scripts/gcc-plugins/gcc-common.h:153:0: warning: "__unused" redefined
>> #define __unused __attribute__((__unused__))
>> ^
> 
> Does the following patch fix your build? (I assume that line is just a
> warning, but if not...)
> 
> diff --git a/scripts/gcc-plugins/gcc-common.h b/scripts/gcc-plugins/gcc-common.h
> index 552d5efd7cb7..17f06079a712 100644
> --- a/scripts/gcc-plugins/gcc-common.h
> +++ b/scripts/gcc-plugins/gcc-common.h
> @@ -150,8 +150,12 @@ void print_gimple_expr(FILE *, gimple, int, int);
>   void dump_gimple_stmt(pretty_printer *, gimple, int, int);
>   #endif
>   
> +#ifndef __unused
>   #define __unused __attribute__((__unused__))
> +#endif
> +#ifndef __visible
>   #define __visible __attribute__((visibility("default")))
> +#endif
>   
>   #define DECL_NAME_POINTER(node) IDENTIFIER_POINTER(DECL_NAME(node))
>   #define DECL_NAME_LENGTH(node) IDENTIFIER_LENGTH(DECL_NAME(node))
> 
>>   HOSTLLD -shared scripts/gcc-plugins/arm_ssp_per_task_plugin.so - due to target missing
>> Undefined symbols for architecture x86_64:
>>   "gen_reg_rtx(machine_mode)", referenced from:
>>       (anonymous namespace)::arm_pertask_ssp_rtl_pass::execute() in arm_ssp_per_task_plugin.o
> 
> However, this part sounds more like what was fixed with
> 259799ea5a9a ("gcc-plugins: arm_ssp_per_task_plugin: Fix for older GCC < 6")
> 
> And maybe some additional fixes for 4.9 are needed?
> 
>> This is because CONFIG_GCC_PLUGIN_ARM_SSP_PER_TASK became automatically enabled and was never
>> before. So the compiler may lack some library search path for building this plugin (which we
>> did never miss).
> 
> Right -- maybe CONFIG_STACKPROTECTOR_PER_TASK doesn't work with old gcc
> 4.9.2? I'll see if I can find that compiler version...
> 

My build environment is based on debian-jessie

$ g++ --version
g++ (Debian 4.9.2-10) 4.9.2

After the fix I posted (which is now commit 259799ea5a9a ("gcc-plugins: 
arm_ssp_per_task_plugin: Fix for older GCC < 6")) I wasn't having any 
more problems.