Re: [PATCH v3 0/4] x86: Rid .head.text of all abs references
From: Borislav Petkov
Date: Thu Nov 07 2024 - 11:00:24 EST
On Wed, Jun 05, 2024 at 12:16:11PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@xxxxxxxxxx>
>
> 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@xxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Brian Gerst <brgerst@xxxxxxxxx>
>
> 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