linux-kernel - Re: [PATCH v6 00/15] x86-64: Stack protector and percpu improvements

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Message-ID: <Z7RRZ0jdqsrADMm0@gmail.com>
Date: Tue, 18 Feb 2025 10:22:47 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Brian Gerst <brgerst@...il.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>, Ard Biesheuvel <ardb@...nel.org>,
	Uros Bizjak <ubizjak@...il.com>
Subject: Re: [PATCH v6 00/15] x86-64: Stack protector and percpu improvements


* 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.
> 
> v6:
> - Rebased to current tip tree
> - Dropped patches already applied
> - Fixed typos in commit messages
> - Added Reviewed-by tags
> 
> Ard Biesheuvel (1):
>   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

>  33 files changed, 100 insertions(+), 475 deletions(-)
>  delete mode 100755 scripts/gcc-x86_32-has-stack-protector.sh
>  delete mode 100755 scripts/gcc-x86_64-has-stack-protector.sh

Thank you for doing this series - it all looks pretty good from my side 
and I've applied it experimentally to tip:x86/asm. I fixed up the trivial 
details other reviewers and me noticed.

Note that the merge is tentative, it might still need a rebase if some 
fundamental problem comes up - but let's see how testing goes in -next.

Thanks,

	Ingo