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

[Ard Biesheuvel]

On Mon, 8 Feb 2021 at 20:07, Kaneda, Erik <erik.kaneda@xxxxxxxxx> wrote:
>
>
>
> > -----Original Message-----
> > From: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> > Sent: Monday, February 8, 2021 5:01 AM
> > To: Shawn Guo <shawn.guo@xxxxxxxxxx>; Ard Biesheuvel
> > <ardb@xxxxxxxxxx>; Kaneda, Erik <erik.kaneda@xxxxxxxxx>
> > Cc: Linux ARM <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>; ACPI Devel Maling
> > List <linux-acpi@xxxxxxxxxxxxxxx>; Linux Kernel Mailing List <linux-
> > kernel@xxxxxxxxxxxxxxx>; open list:ACPI COMPONENT ARCHITECTURE
> > (ACPICA) <devel@xxxxxxxxxx>; Wysocki, Rafael J
> > <rafael.j.wysocki@xxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>; Moore,
> > Robert <robert.moore@xxxxxxxxx>
> > 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@xxxxxxxxxx> 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.