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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Tue, 16 Jun 2020 16:20:41 -0600
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Subject: Re: [PATCH] acpi: disallow loading configfs acpi tables when locked down
To:     Len Brown <lenb@kernel.org>, rjw@rjwysocki.net
Cc:     LKML <linux-kernel@vger.kernel.org>, linux-acpi@vger.kernel.org,
        Kernel Hardening <kernel-hardening@lists.openwall.com>
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Hi Rafael, Len,

Looks like I should have CC'd you on this patch. This is probably
something we should get into 5.8-rc2, so that it can then get put into
stable kernels, as some people think this is security sensitive.
Bigger picture is this:

https://data.zx2c4.com/american-unsigned-language-2.gif
https://data.zx2c4.com/american-unsigned-language-2-fedora-5.8.png

Also, somebody mentioned to me that Microsoft's ACPI implementation
disallows writes to system memory as a security mitigation. I haven't
looked at what that actually entails, but I wonder if entirely
disabling support for ACPI_ADR_SPACE_SYSTEM_MEMORY would be sensible.
I haven't looked at too many DSDTs. Would that break real hardware, or
does nobody do that? Alternatively, the range of acceptable addresses
for SystemMemory could exclude kernel memory. Would that break
anything? Have you heard about Microsoft's mitigation to know more
details on what they figured out they could safely restrict without
breaking hardware? Either way, food for thought I suppose.

Jason