linux-kernel - Re: [PATCH 02/16] x86/build: Remove RWX sections and align on 4KB

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Date:   Thu, 20 Oct 2022 14:15:21 +0300
From:   Evgeniy Baskov <baskov@...ras.ru>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        lvc-project@...uxtesting.org, x86@...nel.org,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 02/16] x86/build: Remove RWX sections and align on 4KB

On 2022-10-19 10:04, Ard Biesheuvel wrote:
> On Tue, 6 Sept 2022 at 12:41, Evgeniy Baskov <baskov@...ras.ru> wrote:
>> 
>> Avoid creating sections with maximal privileges to prepare for W^X
> 
> privileges
> 
>> implementation. Align sections on page size (4KB) to allow protecting
>> them in page table.
>> 
> 
> in the page tables.
> 
>> Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
>> ---
>>  arch/x86/kernel/vmlinux.lds.S | 15 ++++++++-------
>>  1 file changed, 8 insertions(+), 7 deletions(-)
>> 
>> diff --git a/arch/x86/kernel/vmlinux.lds.S 
>> b/arch/x86/kernel/vmlinux.lds.S
>> index 15f29053cec4..6587e0201b50 100644
>> --- a/arch/x86/kernel/vmlinux.lds.S
>> +++ b/arch/x86/kernel/vmlinux.lds.S
>> @@ -102,12 +102,11 @@ jiffies = jiffies_64;
>>  PHDRS {
>>         text PT_LOAD FLAGS(5);          /* R_E */
>>         data PT_LOAD FLAGS(6);          /* RW_ */
>> -#ifdef CONFIG_X86_64
>> -#ifdef CONFIG_SMP
>> +#if defined(CONFIG_X86_64) && defined(CONFIG_SMP)
>>         percpu PT_LOAD FLAGS(6);        /* RW_ */
>>  #endif
>> -       init PT_LOAD FLAGS(7);          /* RWE */
>> -#endif
>> +       inittext PT_LOAD FLAGS(5);      /* R_E */
>> +       init PT_LOAD FLAGS(6);          /* RW_ */
> 
> Please explain in the commit log how this change affects X86_32
> 
>>         note PT_NOTE FLAGS(0);          /* ___ */
>>  }
>> 
>> @@ -226,9 +225,10 @@ SECTIONS
>>  #endif
>> 
>>         INIT_TEXT_SECTION(PAGE_SIZE)
>> -#ifdef CONFIG_X86_64
>> -       :init
>> -#endif
>> +       :inittext
>> +
>> +       . = ALIGN(PAGE_SIZE);
>> +
>> 
>>         /*
>>          * Section for code used exclusively before alternatives are 
>> run. All
>> @@ -240,6 +240,7 @@ SECTIONS
>>         .altinstr_aux : AT(ADDR(.altinstr_aux) - LOAD_OFFSET) {
>>                 *(.altinstr_aux)
>>         }
>> +       :init
>> 
>>         INIT_DATA_SECTION(16)
>> 
>> --
>> 2.35.1
>> 

Thanks for pointing you, I'll fix all mentioned nitpicks before sending
this again.