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

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Date:   Tue, 29 Aug 2023 22:33:16 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     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>
Cc:     linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Kees Cook <keescook@...omium.org>,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] x86/audit: fix -Wmissing-variable-declarations warning for ia32_xyz_class

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
| };
| ...

This patch is similar to commit:
0e5e3d4461a22d73 ("x86/audit: Fix a -Wmissing-prototypes warning for ia32_classify_syscall()") [1]

Link: https://lore.kernel.org/all/20200516123816.2680-1-b.thiel@posteo.de/ [1]
Link: https://github.com/ClangBuiltLinux/linux/issues/1920
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Note: build-tested.
---
 arch/x86/include/asm/audit.h | 7 +++++++
 arch/x86/kernel/audit_64.c   | 5 -----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/audit.h b/arch/x86/include/asm/audit.h
index 36aec57ea7a3..fa918f01333e 100644
--- a/arch/x86/include/asm/audit.h
+++ b/arch/x86/include/asm/audit.h
@@ -4,4 +4,11 @@
 
 int ia32_classify_syscall(unsigned int syscall);
 
+extern unsigned ia32_dir_class[];
+extern unsigned ia32_write_class[];
+extern unsigned ia32_read_class[];
+extern unsigned ia32_chattr_class[];
+extern unsigned ia32_signal_class[];
+
+
 #endif /* _ASM_X86_AUDIT_H */
diff --git a/arch/x86/kernel/audit_64.c b/arch/x86/kernel/audit_64.c
index 44c3601cfdc4..190c120f4285 100644
--- a/arch/x86/kernel/audit_64.c
+++ b/arch/x86/kernel/audit_64.c
@@ -63,11 +63,6 @@ int audit_classify_syscall(int abi, unsigned syscall)
 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[];
-	extern __u32 ia32_signal_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);

---
base-commit: 706a741595047797872e669b3101429ab8d378ef
change-id: 20230829-missingvardecl-audit-493e36f2aa84

Best regards,
--
Justin Stitt <justinstitt@...gle.com>