Re: [PATCH 1/3] module: Rename module_alloc() to text_alloc() and move to kernel proper

From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Ard Biesheuvel <ardb@kernel.org>
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Subject: Re: [PATCH 1/3] module: Rename module_alloc() to text_alloc() and move to kernel proper
Date: Tue, 14 Jul 2020 14:55:30 +0300	[thread overview]
Message-ID: <20200714115530.GC1463346@linux.intel.com> (raw)
In-Reply-To: <CAMj1kXGV_bWehdQvxaMBTOYHXUoFjifBWNpyVy3gaWKktko1mg@mail.gmail.com>

On Tue, Jul 14, 2020 at 01:17:22PM +0300, Ard Biesheuvel wrote:
> > This series essentially does this: introduces text_alloc() and
> > text_memfree(), which have generic implementations in kernel/text.c.
> > Those can be overriddent by arch specific implementations.
> >
> > What you think should be done differently than in my patch set?
> >
> 
> On arm64, module_alloc is only used by the module loader, and so
> pulling it out and renaming it will cause unused code to be
> incorporated into the kernel when building without module support,
> which is the use case you claim to be addressing.

It certainly does not cause the full module loader to be bundle, only
the allocator.

> Module_alloc has semantics that are intimately tied to the module
> loader, but over the years, it ended up being (ab)used by other
> subsystems, which don't require those semantics but just need n pages
> of vmalloc space with executable permissions.
> 
> So the correct approach is to make text_alloc() implement just that,
> generically, and switch bpf etc to use it. Then, only on architectures
> that need it, override it with an implementation that has the required
> additional semantics.
> 
> Refactoring 10+ architectures like this without any regard for how
> text_alloc() deviates from module_alloc() just creates a lot of churn
> that others will have to clean up after you.

Using generic text_alloc() in kernel/kprobes.c would make it behave
differently in arch's that reimplement module_alloc(). That's the main
driver for my approach.

/Jarkko

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