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

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Message-ID: <CAFULd4Z_QoOLKCOawyeFtRe6V4+oaaGxfQxav9dS-Di-Ne7tfw@mail.gmail.com>
Date: Tue, 18 Feb 2025 18:46:38 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Brian Gerst <brgerst@...il.com>, 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>
Subject: Re: [PATCH v6 00/15] x86-64: Stack protector and percpu improvements

On Tue, Feb 18, 2025 at 10:22 AM Ingo Molnar <mingo@...nel.org> wrote:
>
>
> * 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.

I wonder if there would be any benefit if stack canary is put into
struct pcpu_hot?

Uros.