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

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Date:   Wed, 19 Oct 2022 09:04:37 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Evgeniy Baskov <baskov@...ras.ru>
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 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
>