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

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Message-ID: <MWHPR11MB15993FCF4B43A8B7B877265EF08F9@MWHPR11MB1599.namprd11.prod.outlook.com>
Date:   Mon, 8 Feb 2021 19:30:25 +0000
From:   "Kaneda, Erik" <erik.kaneda@...el.com>
To:     Ard Biesheuvel <ardb@...nel.org>
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"



> -----Original Message-----
> From: Ard Biesheuvel <ardb@...nel.org>
> Sent: Monday, February 8, 2021 11:14 AM
> 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.

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