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

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Message-ID: <202308311409.F4EC8BC674@keescook>
Date:   Thu, 31 Aug 2023 14:11:32 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
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 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?)

But otherwise, yes, looks good.

-Kees

-- 
Kees Cook