-----Original Message-----
From: Ard Biesheuvel <ardb@kernel.org>
Sent: Monday, February 8, 2021 11:14 AM
To: Kaneda, Erik <redacted>
Cc: Rafael J. Wysocki <rafael@kernel.org>; Shawn Guo
[off-list ref]; Linux ARM <linux-arm-
kernel@lists.infradead.org>; ACPI Devel Maling List <linux-
acpi@vger.kernel.org>; Linux Kernel Mailing List <linux-
kernel@vger.kernel.org>; open list:ACPI COMPONENT ARCHITECTURE
(ACPICA) [off-list ref]; Wysocki, Rafael J
[off-list ref]; Len Brown [off-list ref]; Moore,
Robert [off-list ref]
Subject: Re: [PATCH] Revert "ACPICA: Interpreter: fix memory leak by using
existing buffer"

On Mon, 8 Feb 2021 at 20:07, Kaneda, Erik [off-list ref] wrote:

quoted

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-----Original Message-----
From: Rafael J. Wysocki <rafael@kernel.org>
Sent: Monday, February 8, 2021 5:01 AM
To: Shawn Guo <redacted>; Ard Biesheuvel
[off-list ref]; Kaneda, Erik [off-list ref]
Cc: Linux ARM <redacted>; ACPI Devel Maling
List [off-list ref]; Linux Kernel Mailing List <linux-
kernel@vger.kernel.org>; open list:ACPI COMPONENT ARCHITECTURE
(ACPICA) [off-list ref]; Wysocki, Rafael J
[off-list ref]; Len Brown [off-list ref]; Moore,
Robert [off-list ref]
Subject: Re: [PATCH] Revert "ACPICA: Interpreter: fix memory leak by

using

quoted

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existing buffer"

On Sat, Feb 6, 2021 at 11:49 AM Shawn Guo [off-list ref]

wrote:

quoted

quoted

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On Sat, Feb 06, 2021 at 09:49:37AM +0100, Ard Biesheuvel wrote:

quoted

This reverts commit 32cf1a12cad43358e47dac8014379c2f33dfbed4.

Hi Bob, Ard and Rafael,

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The 'exisitng buffer' in this case is the firmware provided table, and
we should not modify that in place. This fixes a crash on arm64 with
initrd table overrides, in which case the DSDT is not mapped with
read/write permissions.

Since this code runs on basically every _HID and _CID invocation, I would

have expected this kind of revert to come in for kernels that do not use initrd
override... So it sounds like there is a difference between how pages are
mapped for initrd table overrides and tables exposed through the XSDT for
ARM.. I think it would be easier for us to make these fixes in the future if we
could all come to a consensus on whether if we should assume that these
pages are writable or not.

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Should we assume that all ACPI tables are non-writable and read only

regardless of initrd override and architecture?

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ACPI tables are measured into the TPM on measured boot systems, and
checksummed, so I don't think we should ever modify them in place.

I'm not knowledgeable on TPM but I'm curious - what happens when the TPM detects that these ACPI tables are modified?

But if we need code like this, it should be conditional at the very
least, i.e., it should only rewrite _HIDs and _CIDs if they are
incorrect to begin with.

I agree that this would be a more efficient approach

Erik