linux-kernel - Re: [PATCH v2 1/2] asm-generic/vmlinux.lds: Move .data.rel.ro input into .rodata segment

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Message-ID: <20250220205536.ty7mpvhqmi43zgll@jpoimboe>
Date: Thu, 20 Feb 2025 12:55:36 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
	Huacai Chen <chenhuacai@...nel.org>,
	Ard Biesheuvel <ardb@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] asm-generic/vmlinux.lds: Move .data.rel.ro input
 into .rodata segment

On Wed, Feb 19, 2025 at 11:55:44AM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>

BTW, I was copied on the cover letter but not the individual patches.

> When using -fPIE codegen, the compiler will emit const global objects
> (which are useless unless statically initialized) into .data.rel.ro
> rather than .rodata if the object contains fields that carry absolute
> addresses of other code or data objects. This permits the linker to
> annotate such regions as requiring read-write access only at load time,
> but not at execution time (in user space).

Hm, this sounds more like __ro_after_init, are we sure the kernel
doesn't need to write it early?

> This distinction does not matter for the kernel, but it does imply that
> const data will end up in writable memory if the .data.rel.ro sections
> are not treated in a special way.
> 
> So emit .data.rel.ro into the .rodata segment.

This is a bug fix, right?  Since the RO data wasn't actually RO?  That's
not clear in the title.

-- 
Josh