linux-kernel - Re: [RFC PATCH 27/28] x86/kernel: Switch to PIE linking for the core kernel

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Message-ID: <CAMj1kXEL+BBTpaYzw_vkPdo18gF0-gjxBMbZyuaNhmWZC8=6tw@mail.gmail.com>
Date: Wed, 25 Sep 2024 21:14:28 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Uros Bizjak <ubizjak@...il.com>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>, 
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	Boris Ostrovsky <boris.ostrovsky@...cle.com>, 
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	Masahiro Yamada <masahiroy@...nel.org>, Kees Cook <kees@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Keith Packard <keithp@...thp.com>, 
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	Kan Liang <kan.liang@...ux.intel.com>, linux-doc@...r.kernel.org, 
	linux-pm@...r.kernel.org, kvm@...r.kernel.org, xen-devel@...ts.xenproject.org, 
	linux-efi@...r.kernel.org, linux-arch@...r.kernel.org, 
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	linux-perf-users@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	llvm@...ts.linux.dev, Hou Wenlong <houwenlong.hwl@...group.com>
Subject: Re: [RFC PATCH 27/28] x86/kernel: Switch to PIE linking for the core kernel

On Wed, 25 Sept 2024 at 20:54, Uros Bizjak <ubizjak@...il.com> wrote:
>
> On Wed, Sep 25, 2024 at 5:02 PM Ard Biesheuvel <ardb+git@...gle.com> wrote:
> >
> > From: Ard Biesheuvel <ardb@...nel.org>
> >
> > Build the kernel as a Position Independent Executable (PIE). This
> > results in more efficient relocation processing for the virtual
> > displacement of the kernel (for KASLR). More importantly, it instructs
> > the linker to generate what is actually needed (a program that can be
> > moved around in memory before execution), which is better than having to
> > rely on the linker to create a position dependent binary that happens to
> > tolerate being moved around after poking it in exactly the right manner.
> >
> > Note that this means that all codegen should be compatible with PIE,
> > including Rust objects, so this needs to switch to the small code model
> > with the PIE relocation model as well.
>
> I think that related to this work is the patch series [1] that
> introduces the changes necessary to build the kernel as Position
> Independent Executable (PIE) on x86_64 [1]. There are some more places
> that need to be adapted for PIE. The patch series also introduces
> objtool functionality to add validation for x86 PIE.
>
> [1] "[PATCH RFC 00/43] x86/pie: Make kernel image's virtual address flexible"
> https://lore.kernel.org/lkml/cover.1682673542.git.houwenlong.hwl@antgroup.com/
>

Hi Uros,

I am aware of that discussion, as I took part in it as well.

I don't think any of those changes are actually needed now - did you
notice anything in particular that is missing?