linux-hardening - Re: [PATCH v2] ACPICA: Replace fake flexible arrays with flexible array members

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Date:   Fri, 27 Jan 2023 20:51:10 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        devel@...ica.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] ACPICA: Replace fake flexible arrays with flexible
 array members

On Fri, Jan 27, 2023 at 8:47 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Fri, Jan 27, 2023 at 08:43:05PM +0100, Rafael J. Wysocki wrote:
> > On Fri, Jan 27, 2023 at 8:16 PM Kees Cook <keescook@...omium.org> wrote:
> > >
> > > 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.
> > >
> > > Link: https://github.com/acpica/acpica/pull/813
> > > Signed-off-by: Kees Cook <keescook@...omium.org>
> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > ---
> > > v2: include stddef.h and switch to __DECLARE_FLEX_ARRAY()
> > > v1: https://lore.kernel.org/lkml/20221118181538.never.225-kees@kernel.org/
> > > ---
> > >  include/acpi/acrestyp.h | 9 +++++++--
> > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/acpi/acrestyp.h b/include/acpi/acrestyp.h
> > > index a7fb8ddb3dc6..250046a7c870 100644
> > > --- a/include/acpi/acrestyp.h
> > > +++ b/include/acpi/acrestyp.h
> > > @@ -10,6 +10,8 @@
> > >  #ifndef __ACRESTYP_H__
> > >  #define __ACRESTYP_H__
> > >
> > > +#include <linux/stddef.h>
> > > +
> > >  /*
> > >   * Definitions for Resource Attributes
> > >   */
> > > @@ -332,7 +334,7 @@ struct acpi_resource_extended_irq {
> > >         u8 wake_capable;
> > >         u8 interrupt_count;
> > >         struct acpi_resource_source resource_source;
> > > -       u32 interrupts[1];
> > > +       u32 interrupts[];
> > >  };
> > >
> > >  struct acpi_resource_generic_register {
> > > @@ -679,7 +681,10 @@ struct acpi_pci_routing_table {
> > >         u32 pin;
> > >         u64 address;            /* here for 64-bit alignment */
> > >         u32 source_index;
> > > -       char source[4];         /* pad to 64 bits so sizeof() works in all cases */
> > > +       union {
> > > +               char pad[4];    /* pad to 64 bits so sizeof() works in all cases */
> > > +               __DECLARE_FLEX_ARRAY(char, source);
> > > +       };
> > >  };
> > >
> > >  #endif                         /* __ACRESTYP_H__ */
> > > --
> >
> > With this applied I get:
> >
> > rafael@...tch:~/work/linux-pm/tools/power/acpi> make
> >  DESCEND tools/acpidbg
> >  MKDIR    include
> >  CP       include
> >  CC       tools/acpidbg/acpidbg.o
> > In file included from
> > /scratch/rafael/work/linux-pm/tools/power/acpi/include/acpi/acpi.h:27:0,
> >                 from acpidbg.c:9:
> > /scratch/rafael/work/linux-pm/tools/power/acpi/include/acpi/acrestyp.h:686:3:
> > error: expected specif
> > ier-qualifier-list before ‘__DECLARE_FLEX_ARRAY’
> >   __DECLARE_FLEX_ARRAY(char, source);
> >   ^~~~~~~~~~~~~~~~~~~~
> > make[1]: *** [../../Makefile.rules:25:
> > /scratch/rafael/work/linux-pm/tools/power/acpi/tools/acpidbg/
> > acpidbg.o] Error 1
> > make: *** [Makefile:18: acpidbg] Error 2
> >
> > The tools build successfully without it.
>
> I think a "make clean" is needed first? It builds for me...

I think that the default user space header files on this machine may
not be up to date.

I'll apply the v2, thanks!