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

Ard Biesheuvel
2024-09-25T19:14:41Z

On Wed, 25 Sept 2024 at 20:54, Uros Bizjak <ubizjak@gmail.com> wrote:
>
> On Wed, Sep 25, 2024 at 5:02 PM Ard Biesheuvel <ardb+git@google.com> wrote:
> >
> > From: Ard Biesheuvel <ardb@kernel.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?