linux-hardening - Re: [PATCH v5 02/27] x86/build: Remove RWX sections and align on 4KB

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Date:   Wed, 5 Apr 2023 19:40:59 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Evgeniy Baskov <baskov@...ras.ru>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        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>,
        Peter Jones <pjones@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        "Limonciello, Mario" <mario.limonciello@....com>,
        joeyli <jlee@...e.com>, 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 v5 02/27] x86/build: Remove RWX sections and align on 4KB

On Tue, Mar 14, 2023 at 01:13:29PM +0300, Evgeniy Baskov wrote:
> Avoid creating sections simultaneously writable and readable to prepare
> for W^X implementation for the kernel itself (not the decompressor).
> Align kernel sections on page size (4KB) to allow protecting them in the
> page tables.
> 
> Split init code form ".init" segment into separate R_X ".inittext"

s/form/from/

> segment and make ".init" segment non-executable.

"... and make the .init segment RW_."

> Also add these segments to x86_32 architecture for consistency.

Same comment as before: please refrain from talking about the *what* in
a commit message but about the *why*.

And considering the matter, you have a *lot* of *why* to talk about. :-)

Pls check your whole set.

> Currently paging is disabled in x86_32 in compressed kernel, so
> protection is not applied anyways, but .init code was incorrectly
> placed in non-executable ".data" segment. This should not change
> anything meaningful in memory layout now, but might be required in case
> memory protection will also be implemented in compressed kernel for
> x86_32.

I highly doubt that - no one cares about 32-bit x86 anymore.

> @@ -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

Why isn't this placed after inittext but here?

I'm thinking you wanna have:

	:inittext
	. = ALIGN..
	:init
	<rest>

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette