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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Fri, 16 Feb 2024 17:53:10 +0100
Message-ID: <CAJZ5v0jkp2SP5DDg5eYkZu9_buQ7i2isGfgJYvD2ZHFKtTr_DA@mail.gmail.com>
Subject: Re: [PATCH v3] ACPI: Drop the custom_method debugfs interface
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>, Linux ACPI <linux-acpi@vger.kernel.org>, 
	LKML <linux-kernel@vger.kernel.org>, Zhang Rui <rui.zhang@intel.com>, 
	Kees Cook <kees@kernel.org>, "shiqiang.deng" <shiqiang.deng213@gmail.com>, 
	Sebastian Grzywna <swiftgeek@gmail.com>, Hang Zhang <zh.nvgt@gmail.com>
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On Fri, Feb 16, 2024 at 5:50=E2=80=AFPM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Fri, Feb 16, 2024 at 05:38:55PM +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > The ACPI custom_method debugfs interface is security-sensitive and
> > concurrent access to it is broken [1].
> >
> > Moreover, the recipe for preparing a customized version of a given
> > control method has changed at one point due to ACPICA changes, which
> > has not been reflected in its documentation, so whoever used it before
> > has had to adapt and it had gone unnoticed for a long time.
> >
> > This interface was a bad idea to start with and its implementation is
> > fragile at the design level.  It's been always conceptually questionabl=
e,
> > problematic from the security standpoint and implemented poorly.
> >
> > Patches fixing its most apparent functional issues (for example, [2]) d=
on't
> > actually address much of the above.
> >
> > Granted, at the time it was introduced, there was no alternative, but
> > there is the AML debugger in the kernel now and there is the configfs
> > interface allowing custom ACPI tables to be loaded.  The former can be
> > used for extensive AML debugging and the latter can be use for testing
> > new AML. [3]
> >
> > Accordingly, drop custom_method along with its (outdated anyway)
> > documentation.
> >
> > Link: https://lore.kernel.org/linux-acpi/20221227063335.61474-1-zh.nvgt=
@gmail.com/ # [1]
> > https://lore.kernel.org/linux-acpi/20231111132402.4142-1-shiqiang.deng2=
13@gmail.com/ [2]
> > https://stackoverflow.com/questions/62849113/how-to-unload-an-overlay-l=
oaded-using-acpi-config-sysfs # [3]
>
> I believe you missed Link: tags for 2 and 3.

Obviously, you are right.

That's easy to fix, though, and I'd rather not confuse people by
sending a v4 just because of this.

> > Reported-by: Hang Zhang <zh.nvgt@gmail.com>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Reviewed-by: Zhang Rui <rui.zhang@intel.com>