linux-hardening - Re: [PATCH] ACPICA: Replace fake flexible arrays with flexible array members

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Message-ID: <CAJZ5v0hQypNonoqr1V1xqN5bX+pKBF3AR=F-mRynN5yvcS9kyA@mail.gmail.com>
Date:   Fri, 27 Jan 2023 19:08:39 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org,
        acpica-devel@...ts.linuxfoundation.org
Subject: Re: [PATCH] ACPICA: Replace fake flexible arrays with flexible array members

On Fri, Jan 20, 2023 at 8:16 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Fri, Jan 20, 2023 at 07:10:52PM +0100, Rafael J. Wysocki wrote:
> > On Sun, Jan 15, 2023 at 7:38 PM Kees Cook <keescook@...omium.org> wrote:
> > >
> > > On Fri, Nov 18, 2022 at 10:15:51AM -0800, Kees Cook wrote:
> > > > Functionally identical to ACPICA upstream pull request 813:
> > > > https://github.com/acpica/acpica/pull/813
> > >
> > > Any update on this? Upstream is currently unbuildable since October.
> > >
> > > > One-element arrays (and multi-element arrays being treated as
> > > > dynamically sized) are deprecated[1] and are being replaced with
> > > > flexible array members in support of the ongoing efforts to tighten the
> > > > FORTIFY_SOURCE routines on memcpy(), correctly instrument array indexing
> > > > with UBSAN_BOUNDS, and to globally enable -fstrict-flex-arrays=3.
> > > >
> > > > Replace one-element array with flexible-array member in struct
> > > > acpi_resource_extended_irq. Replace 4-byte fixed-size array with 4-byte
> > > > padding in a union with a flexible-array member in struct
> > > > acpi_pci_routing_table.
> > > >
> > > > This results in no differences in binary output.
> > >
> > > In the meantime, can you take this patch for Linux, and we can wait for
> > > ACPICA to catch up?
> >
> > Applied now (as 6.3 material), sorry for the delay.
>
> Thanks!

Unfortunately, this breaks compilation for the ACPI tools in tools/power/acpi/.

Apparently, the problem is that DECLARE_FLEX_ARRAY() is not defined
when the tools are built, because kernel headers are not used then.

I guess the changes from your upstream PR need to be backported
literally for this to work, so I'll drop this one for the time being.
Or please let me know if you have a better idea.