On Thu, 8 May 2025 at 14:23, Marco Elver [off-list ref] wrote:

+Cc KCOV maintainers

On Wed, 7 May 2025 at 20:16, Kees Cook [off-list ref] wrote:

quoted

While __noinstr already contained __no_sanitize_coverage, it needs to
be added to __init and __head section markings to support the Clang
implementation of CONFIG_STACKLEAK. This is to make sure the stack depth
tracking callback is not executed in unsupported contexts.

The other sanitizer coverage options (trace-pc and trace-cmp) aren't
needed in __head nor __init either ("We are interested in code coverage
as a function of a syscall inputs"[1]), so this appears safe to disable
for them as well.

@ Dmitry, Aleksandr - Will this produce some unwanted side-effects for
syzbot? I also think it's safe, but just double checking.

I do not see any problems with this.

quoted

Link: https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/kcov.c?h=v6.14#n179 [1]
Signed-off-by: Kees Cook <kees@kernel.org>

Acked-by: Marco Elver <elver@google.com>

quoted

---
Cc: Marco Elver <elver@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Thomas Gleixner <redacted>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <x86@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: "Kirill A. Shutemov" <redacted>
Cc: Hou Wenlong <redacted>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christophe Leroy <redacted>
Cc: <redacted>
---
 arch/x86/include/asm/init.h | 2 +-
 include/linux/init.h        | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h
index 8b1b1abcef15..6bfdaeddbae8 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
+#define __head __section(".head.text") __no_sanitize_undefined __no_sanitize_coverage
 #endif

 struct x86_mapping_info {

diff --git a/include/linux/init.h b/include/linux/init.h
index ee1309473bc6..c65a050d52a7 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h

@@ -49,7 +49,9 @@

 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init         __section(".init.text") __cold  __latent_entropy __noinitretpoline
+#define __init         __section(".init.text") __cold __latent_entropy \
+                                               __noinitretpoline       \
+                                               __no_sanitize_coverage
 #define __initdata     __section(".init.data")
 #define __initconst    __section(".init.rodata")
 #define __exitdata     __section(".exit.data")
--

2.34.1