linux-kernel - Re: [PATCH v5 00/16] x86-64: Stack protector and percpu improvements

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Message-ID: <CAMj1kXE3x8cAK7PeYOcF9WQkwJbhjRBZkoUf2qzPvBbyVWUMGA@mail.gmail.com>
Date: Sat, 4 Jan 2025 10:14:34 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Brian Gerst <brgerst@...il.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, 
	Ingo Molnar <mingo@...nel.org>, "H . Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Borislav Petkov <bp@...en8.de>, Uros Bizjak <ubizjak@...il.com>
Subject: Re: [PATCH v5 00/16] x86-64: Stack protector and percpu improvements

On Tue, 5 Nov 2024 at 16:58, Brian Gerst <brgerst@...il.com> wrote:
>
> Currently, x86-64 uses an unusual percpu layout, where the percpu section
> is linked at absolute address 0.  The reason behind this is that older GCC
> versions placed the stack protector (if enabled) at a fixed offset from the
> GS segment base.  Since the GS segement is also used for percpu variables,
> this forced the current layout.
>
> GCC since version 8.1 supports a configurable location for the stack
> protector value, which allows removal of the restriction on how the percpu
> section is linked.  This allows the percpu section to be linked normally,
> like other architectures.  In turn, this allows removal of code that was
> needed to support the zero-based percpu section.
>
> v5:
> - Added two patches from Ard Biesheuvel to make stack protector work
>   properly when compiling with clang.
> - Raise minimum GCC version to 8.1 for x86.
> - Drop objtool conversion code.
>
> Ard Biesheuvel (2):
>   x86/stackprotector: Work around strict Clang TLS symbol requirements
>   x86/module: Deal with GOT based stack cookie load on Clang < 17
>
> Brian Gerst (14):
>   x86: Raise minimum GCC version to 8.1
>   x86/stackprotector: Remove stack protector test scripts
>   x86/boot: Disable stack protector for early boot code
>   x86/pvh: Use fixed_percpu_data for early boot GSBASE
>   x86/relocs: Handle R_X86_64_REX_GOTPCRELX relocations
>   x86/stackprotector/64: Convert to normal percpu variable
>   x86/percpu/64: Use relative percpu offsets
>   x86/percpu/64: Remove fixed_percpu_data
>   x86/boot/64: Remove inverse relocations
>   x86/percpu/64: Remove INIT_PER_CPU macros
>   percpu: Remove PER_CPU_FIRST_SECTION
>   percpu: Remove PERCPU_VADDR()
>   percpu: Remove __per_cpu_load
>   kallsyms: Remove KALLSYMS_ABSOLUTE_PERCPU
>

For the series,

Reviewed-by: Ard Biesheuvel <ardb@...nel.org>