linux-kernel - Re: [syzbot] upstream build error (23)

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Message-ID: <202507291524.BA4DC7E1B9@keescook>
Date: Tue, 29 Jul 2025 15:27:08 -0700
From: Kees Cook <kees@...nel.org>
To: Linus Torvalds <torvalds@...uxfoundation.org>
Cc: Borislav Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>,
	syzbot <syzbot+5245cb609175fb6e8122@...kaller.appspotmail.com>,
	dave.hansen@...ux.intel.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, mingo@...hat.com,
	syzkaller-bugs@...glegroups.com, x86@...nel.org
Subject: Re: [syzbot] upstream build error (23)

On Tue, Jul 29, 2025 at 03:11:50PM -0700, Linus Torvalds wrote:
> Which is supposed to _lessen_ the sanitizer coverage by adding the
> __attribute__((no_sanitize("coverage"))), but it's clearly causing
> more problems and making gcc just do crazy things.

Since this change was only made for Clang's stack depth coverage
analysis, let's drop it from GCC builds? I'm testing this currently:

diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h
index 6bfdaeddbae8..5a68e9db6518 100644
--- a/arch/x86/include/asm/init.h
+++ b/arch/x86/include/asm/init.h
@@ -5,7 +5,7 @@
 #if defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 170000
 #define __head	__section(".head.text") __no_sanitize_undefined __no_stack_protector
 #else
-#define __head	__section(".head.text") __no_sanitize_undefined __no_sanitize_coverage
+#define __head	__section(".head.text") __no_sanitize_undefined __no_kstack_erase
 #endif
 
 struct x86_mapping_info {
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 2b77d12e07b2..89e2c01fc8b1 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -378,6 +378,13 @@ struct ftrace_likely_data {
 # define __signed_wrap
 #endif
 
+/* GCC does not like splitting sanitizer coverage across section inlines */
+#ifdef CC_IS_CLANG
+#define __no_kstack_erase	__no_sanitize_coverage
+#else
+#define __no_kstack_erase
+#endif
+
 /* Section for code which can't be instrumented at all */
 #define __noinstr_section(section)					\
 	noinline notrace __attribute((__section__(section)))		\
diff --git a/include/linux/init.h b/include/linux/init.h
index c65a050d52a7..a60d32d227ee 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -51,7 +51,7 @@
    discard it in modules) */
 #define __init		__section(".init.text") __cold __latent_entropy	\
 						__noinitretpoline	\
-						__no_sanitize_coverage
+						__no_kstack_erase
 #define __initdata	__section(".init.data")
 #define __initconst	__section(".init.rodata")
 #define __exitdata	__section(".exit.data")

-- 
Kees Cook