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Date: Fri, 16 Feb 2024 11:26:14 -0800
From: Kees Cook <keescook@chromium.org>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Linux ACPI <linux-acpi@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	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>
Subject: Re: [PATCH v3] ACPI: Drop the custom_method debugfs interface
Message-ID: <202402161125.3137F917DC@keescook>
References: <6029478.lOV4Wx5bFT@kreacher>
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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 questionable,
> problematic from the security standpoint and implemented poorly.
> 
> Patches fixing its most apparent functional issues (for example, [2]) don'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 Accordingly, drop custom_method along with its (outdated anyway)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.deng213@gmail.com/ [2]
> https://stackoverflow.com/questions/62849113/how-to-unload-an-overlay-loaded-using-acpi-config-sysfs # [3]
> Reported-by: Hang Zhang <zh.nvgt@gmail.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Yay! Happy to see this removed. :)

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook