linux-kernel - Re: [PATCH v3 0/4] x86: Rid .head.text of all abs references

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Message-ID: <20241107155941.GAZyzj7bhkavHswsI3@fat_crate.local>
Date: Thu, 7 Nov 2024 16:59:41 +0100
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
	Tom Lendacky <thomas.lendacky@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH v3 0/4] x86: Rid .head.text of all abs references

On Wed, Jun 05, 2024 at 12:16:11PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> This series removes the last remaining absolute symbol references from
> .head.text. Doing so is necessary because code in this section may be
> called from a 1:1 mapping of memory, which deviates from the mapping
> this code was linked and/or relocated to run at. This is not something
> that the toolchains support: even PIC/PIE code is still assumed to
> execute from the same mapping that it was relocated to run from by the
> startup code or dynamic loader. This means we are basically on our own
> here, and need to add measures to ensure the code works as expected in
> this manner.
> 
> Given that the startup code needs to create the kernel virtual mapping
> in the page tables, early references to some kernel virtual addresses
> are valid even if they cannot be dereferenced yet. To avoid having to
> make this distinction at build time, patches #3 and #4 replace such
> valid references with RIP-relative references with an offset applied.
> 
> Patches #1 and #2 remove some absolute references from .head.text that
> don't need to be there in the first place.
> 
> Changes since v2:
> - Rebase onto v6.10-rc2
> - Tweak commit log of patch #3
> 
> Changes since v1/RFC:
> - rename va_offset to p2v_offset
> - take PA of _text in C code directly
> 
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Brian Gerst <brgerst@...il.com>
> 
> Ard Biesheuvel (4):
>   x86/sev: Avoid WARN()s in early boot code
>   x86/xen/pvh: Move startup code into .ref.text
>   x86/boot/64: Determine VA/PA offset before entering C code
>   x86/boot/64: Avoid intentional absolute symbol references in
>     .head.text

Those look forgotten in my mbox. Do we still want them to go somewhere?

Thx.

-- 
Regards/Gruss,
    Boris.

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