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

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Message-ID: <CAJZ5v0iV5wK4gsoadmWOyof_vzaAOx8oX0DJu+1-bCQNdNJtBQ@mail.gmail.com>
Date:   Fri, 27 Jan 2023 20:43:05 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        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 8:16 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.