linux-kernel - Re: [PATCH] Revert "ACPICA: Interpreter: fix memory leak by using existing buffer"

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Date:   Mon, 8 Feb 2021 20:13:54 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     "Kaneda, Erik" <erik.kaneda@...el.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Shawn Guo <shawn.guo@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@...ica.org>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        Len Brown <lenb@...nel.org>,
        "Moore, Robert" <robert.moore@...el.com>
Subject: Re: [PATCH] Revert "ACPICA: Interpreter: fix memory leak by using
 existing buffer"

On Mon, 8 Feb 2021 at 20:07, Kaneda, Erik <erik.kaneda@...el.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Rafael J. Wysocki <rafael@...nel.org>
> > Sent: Monday, February 8, 2021 5:01 AM
> > To: Shawn Guo <shawn.guo@...aro.org>; Ard Biesheuvel
> > <ardb@...nel.org>; Kaneda, Erik <erik.kaneda@...el.com>
> > Cc: Linux ARM <linux-arm-kernel@...ts.infradead.org>; ACPI Devel Maling
> > List <linux-acpi@...r.kernel.org>; Linux Kernel Mailing List <linux-
> > kernel@...r.kernel.org>; open list:ACPI COMPONENT ARCHITECTURE
> > (ACPICA) <devel@...ica.org>; Wysocki, Rafael J
> > <rafael.j.wysocki@...el.com>; Len Brown <lenb@...nel.org>; Moore,
> > Robert <robert.moore@...el.com>
> > Subject: Re: [PATCH] Revert "ACPICA: Interpreter: fix memory leak by using
> > existing buffer"
> >
> > On Sat, Feb 6, 2021 at 11:49 AM Shawn Guo <shawn.guo@...aro.org> wrote:
> > >
> > > On Sat, Feb 06, 2021 at 09:49:37AM +0100, Ard Biesheuvel wrote:
> > > > This reverts commit 32cf1a12cad43358e47dac8014379c2f33dfbed4.
> > > >
>
> Hi Bob, Ard and Rafael,
>
> > > > 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.
>
> Should we assume that all ACPI tables are non-writable and read only regardless of initrd override and architecture?
>

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.

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.