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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Mon, 8 Feb 2021 20:13:54 +0100
Message-ID: <CAMj1kXGwedPfS0xBJn9XXoLVVH44eNmKykf7LdGOgOJ4qPqQiw@mail.gmail.com>
Subject: Re: [PATCH] Revert "ACPICA: Interpreter: fix memory leak by using
 existing buffer"
To:     "Kaneda, Erik" <erik.kaneda@intel.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Shawn Guo <shawn.guo@linaro.org>,
        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)" <devel@acpica.org>,
        "Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
        Len Brown <lenb@kernel.org>,
        "Moore, Robert" <robert.moore@intel.com>
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On Mon, 8 Feb 2021 at 20:07, Kaneda, Erik <erik.kaneda@intel.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Rafael J. Wysocki <rafael@kernel.org>
> > Sent: Monday, February 8, 2021 5:01 AM
> > To: Shawn Guo <shawn.guo@linaro.org>; Ard Biesheuvel
> > <ardb@kernel.org>; Kaneda, Erik <erik.kaneda@intel.com>
> > Cc: 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) <devel@acpica.org>; Wysocki, Rafael J
> > <rafael.j.wysocki@intel.com>; Len Brown <lenb@kernel.org>; Moore,
> > Robert <robert.moore@intel.com>
> > Subject: Re: [PATCH] Revert "ACPICA: Interpreter: fix memory leak by us=
ing
> > existing buffer"
> >
> > On Sat, Feb 6, 2021 at 11:49 AM Shawn Guo <shawn.guo@linaro.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 wit=
h
> > > > 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 i=
nitrd 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 futu=
re 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 rega=
rdless 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.