Re: [PATCH 2/8] init.h: Disable sanitizer coverage for __init and __head

[Marco Elver]

+Cc KCOV maintainers

On Wed, 7 May 2025 at 20:16, Kees Cook <kees@xxxxxxxxxx> wrote:
>
> 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.

> 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@xxxxxxxxxx>

Acked-by: Marco Elver <elver@xxxxxxxxxx>

> ---
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: <x86@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
> Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> Cc: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> Cc: <kasan-dev@xxxxxxxxxxxxxxxx>
> ---
>  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
>