linux-kernel - Re: [PATCH 2/3] x86:add missing CONFIG_STRICT_KERNEL_RWX for mark_rodata

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Date:   Wed, 30 May 2018 08:07:10 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     nixiaoming <nixiaoming@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        James Morse <james.morse@....com>,
        Kristina Martsenko <kristina.martsenko@....com>,
        Steve Capper <steve.capper@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        zhang.jia@...ux.alibaba.com,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        linux-s390 <linux-s390@...r.kernel.org>
Subject: Re: [PATCH 2/3] x86:add missing CONFIG_STRICT_KERNEL_RWX for mark_rodata_ro

On 30 May 2018 at 07:58, Ingo Molnar <mingo@...nel.org> wrote:
>
> * nixiaoming <nixiaoming@...wei.com> wrote:
>
>> mark_rodata_ro is only called by the function mark_readonly
>> when CONFIG_STRICT_KERNEL_RWX=y
>>
>> if CONFIG_STRICT_KERNEL_RWX is not set
>> a compile warning may be triggered: unused function
>>
>> Signed-off-by: nixiaoming <nixiaoming@...wei.com>
>> ---
>>  arch/x86/mm/init_32.c | 2 ++
>>  arch/x86/mm/init_64.c | 2 ++
>>  2 files changed, 4 insertions(+)
>>
>> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
>> index c893c6a..121c567 100644
>> --- a/arch/x86/mm/init_32.c
>> +++ b/arch/x86/mm/init_32.c
>> @@ -920,6 +920,7 @@ static void mark_nxdata_nx(void)
>>       set_pages_nx(virt_to_page(start), size >> PAGE_SHIFT);
>>  }
>>
>> +#ifdef CONFIG_STRICT_KERNEL_RWX
>>  void mark_rodata_ro(void)
>>  {
>>       unsigned long start = PFN_ALIGN(_text);
>> @@ -957,3 +958,4 @@ void mark_rodata_ro(void)
>>       if (__supported_pte_mask & _PAGE_NX)
>>               debug_checkwx();
>>  }
>> +#endif /*end of CONFIG_STRICT_KERNEL_RWX*/
>> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
>> index 0a40060..1b7a1a7 100644
>> --- a/arch/x86/mm/init_64.c
>> +++ b/arch/x86/mm/init_64.c
>> @@ -1245,6 +1245,7 @@ void set_kernel_text_ro(void)
>>       set_memory_ro(start, (end - start) >> PAGE_SHIFT);
>>  }
>>
>> +#ifdef CONFIG_STRICT_KERNEL_RWX
>>  void mark_rodata_ro(void)
>>  {
>>       unsigned long start = PFN_ALIGN(_text);
>> @@ -1298,6 +1299,7 @@ void mark_rodata_ro(void)
>>        */
>>       pti_clone_kernel_text();
>>  }
>> +#endif
>
> NAK, this is very ugly and the changelog doesn't appear to be true: the build
> warning does not trigger in the default build, correct?
>

I don't see how the build warning could trigger at all, given that
mark_rodata_ro() has external linkage.