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

[Dmitry Vyukov <dvyukov@google.com>]

On Thu, 8 May 2025 at 14:23, Marco Elver <elver@google.com> wrote:
>
> +Cc KCOV maintainers
>
> On Wed, 7 May 2025 at 20:16, Kees Cook <kees@kernel.org> 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.

I do not see any problems with this.

> > 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>
>
> > ---
> > Cc: Marco Elver <elver@google.com>
> > Cc: Andrey Konovalov <andreyknvl@gmail.com>
> > Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > 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" <kirill.shutemov@linux.intel.com>
> > Cc: Hou Wenlong <houwenlong.hwl@antgroup.com>
> > 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 <christophe.leroy@csgroup.eu>
> > Cc: <kasan-dev@googlegroups.com>
> > ---
> >  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
> >