linux-kernel - Re: [PATCH] x86/audit: fix -Wmissing-variable-declarations warning for ia32_xyz

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Message-ID: <CAFhGd8rZdRw1EX-=d7o57TqUc2OacNK-Uciniup=bvtyfsoxgw@mail.gmail.com>
Date:   Thu, 31 Aug 2023 16:18:10 -0700
From:   Justin Stitt <justinstitt@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] x86/audit: fix -Wmissing-variable-declarations warning
 for ia32_xyz_class

On Thu, Aug 31, 2023 at 2:11 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Tue, Aug 29, 2023 at 10:33:16PM +0000, Justin Stitt wrote:
> > When building x86 defconfig with Clang-18 I get the following warnings:
> > | arch/x86/ia32/audit.c:6:10: warning: no previous extern declaration for non-static variable 'ia32_dir_class' [-Wmissing-variable-declarations]
> > |     6 | unsigned ia32_dir_class[] = {
> > | arch/x86/ia32/audit.c:11:10: warning: no previous extern declaration for non-static variable 'ia32_chattr_class' [-Wmissing-variable-declarations]
> > |    11 | unsigned ia32_chattr_class[] = {
> > | arch/x86/ia32/audit.c:16:10: warning: no previous extern declaration for non-static variable 'ia32_write_class' [-Wmissing-variable-declarations]
> > |    16 | unsigned ia32_write_class[] = {
> > | arch/x86/ia32/audit.c:21:10: warning: no previous extern declaration for non-static variable 'ia32_read_class' [-Wmissing-variable-declarations]
> > |    21 | unsigned ia32_read_class[] = {
> > | arch/x86/ia32/audit.c:26:10: warning: no previous extern declaration for non-static variable 'ia32_signal_class' [-Wmissing-variable-declarations]
> > |    26 | unsigned ia32_signal_class[] = {
> >
> > These warnings occur due to their respective extern declarations being
> > scoped inside of audit_classes_init as well as only being enabled with
> > `CONFIG_IA32_EMULATION=y`:
> > | static int __init audit_classes_init(void)
> > | {
> > | #ifdef CONFIG_IA32_EMULATION
> > |     extern __u32 ia32_dir_class[];
> > |     extern __u32 ia32_write_class[];
> > |     extern __u32 ia32_read_class[];
> > |     extern __u32 ia32_chattr_class[];
> > |     audit_register_class(AUDIT_CLASS_WRITE_32, ia32_write_class);
> > |     audit_register_class(AUDIT_CLASS_READ_32, ia32_read_class);
> > |     audit_register_class(AUDIT_CLASS_DIR_WRITE_32, ia32_dir_class);
> > |     audit_register_class(AUDIT_CLASS_CHATTR_32, ia32_chattr_class);
> > | #endif
> > |     audit_register_class(AUDIT_CLASS_WRITE, write_class);
> > |     audit_register_class(AUDIT_CLASS_READ, read_class);
> > |     audit_register_class(AUDIT_CLASS_DIR_WRITE, dir_class);
> > |     audit_register_class(AUDIT_CLASS_CHATTR, chattr_class);
> > |     return 0;
> > | }
> >
> > Lift the extern declarations to their own header and resolve scoping
> > issues (and thus fix the warnings).
> >
> > Moreover, change __u32 to unsigned so that we match the definitions:
> > | unsigned ia32_dir_class[] = {
> > | #include <asm-generic/audit_dir_write.h>
> > | ~0U
> > | };
> > |
> > | unsigned ia32_chattr_class[] = {
> > | #include <asm-generic/audit_change_attr.h>
> > | ~0U
> > | };
> > | ...
>
> I would expect checkpatch to warn about bare "unsigned", which is frown
> on these days. :) I think __u32 should be fine here...? (Why is it __u32
> instead of u32, btw?)

Yeah, checkpatch doesn't like it. I was just trying to mirror the
implementation in audit.c as closely as possible:
|     unsigned ia32_dir_class[] = {
|       #include <asm-generic/audit_dir_write.h>
|       ~0U
|     };


>
> But otherwise, yes, looks good.

Thanks for the feedback here. Should I send a v2 where I changed _all_
instances of `unsigned` in both audit.c and audit.h to be `u32`? Or
perhaps, `unsigned int`.

>
> -Kees
>
> --
> Kees Cook