On Wed, 30 Jul 2025 at 01:41, Kees Cook <k...@kernel.org> wrote:
>
> In order to support Clang's stack depth tracking (for Linux's kstack_erase
> feature), the coverage sanitizer needed to be disabled for __init (and
> __head) section code. Doing this universally (i.e. for GCC too) created
> a number of unexpected problems, ranging from changes to inlining logic
> to failures to DCE code on earlier GCC versions.
>
> Since this change is only needed for Clang, specialize it so that GCC
> doesn't see the change as it isn't needed there (the GCC implementation
> of kstack_erase uses a GCC plugin that removes stack depth tracking
> instrumentation from __init sections during a late pass in the IR).
>
> Successfully build and boot tested with GCC 12 and Clang 22.
>
> Fixes: 381a38ea53d2 ("init.h: Disable sanitizer coverage for __init and
> __head")
> Reported-by: kernel test robot <l...@intel.com>
> Closes:
> https://lore.kernel.org/oe-kbuild-all/202507270258.newuixld-...@intel.com/
> Reported-by: syzbot+5245cb609175fb6e8...@syzkaller.appspotmail.com
> Closes:
> https://lore.kernel.org/all/6888d004.a00a0220.26d0e1.0004....@google.com/
> Signed-off-by: Kees Cook <k...@kernel.org>
Looks good:
Reviewed-by: Marco Elver <el...@google.com>
> ---
> v2: correctly split compiler-specific stuff out of compiler_types.h (Miguel)
> v1: https://lore.kernel.org/all/20250729224325.work.019-k...@kernel.org/
> Cc: Linus Torvalds <torva...@linuxfoundation.org>
> Cc: Miguel Ojeda <oj...@kernel.org>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Borislav Petkov <b...@alien8.de>
> Cc: Dave Hansen <dave.han...@linux.intel.com>
> Cc: <x...@kernel.org>
> Cc: "H. Peter Anvin" <h...@zytor.com>
> Cc: Ard Biesheuvel <a...@kernel.org>
> Cc: Marco Elver <el...@google.com>
> Cc: Hou Wenlong <houwenlong....@antgroup.com>
> Cc: Kirill A. Shutemov <k...@kernel.org>
> Cc: Nathan Chancellor <nat...@kernel.org>
> Cc: Przemek Kitszel <przemyslaw.kits...@intel.com>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Masahiro Yamada <masahi...@kernel.org>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Wei Yang <richard.weiy...@gmail.com>
> Cc: Sami Tolvanen <samitolva...@google.com>
> Cc: Arnd Bergmann <a...@arndb.de>
> Cc: Christophe Leroy <christophe.le...@csgroup.eu>
> ---
> arch/x86/include/asm/init.h | 2 +-
> include/linux/compiler-clang.h | 3 +++
> include/linux/compiler_types.h | 4 ++++
> include/linux/init.h | 2 +-
> 4 files changed, 9 insertions(+), 2 deletions(-)
>
> 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-clang.h b/include/linux/compiler-clang.h
> index 4fc8e26914ad..fa4ffe037bc7 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -89,6 +89,9 @@
> #define __no_sanitize_coverage
> #endif
>
> +/* Only Clang needs to disable the coverage sanitizer for kstack_erase. */
> +#define __no_kstack_erase __no_sanitize_coverage
> +
> #if __has_feature(shadow_call_stack)
> # define __noscs __attribute__((__no_sanitize__("shadow-call-stack")))
> #endif
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 2b77d12e07b2..16755431fc11 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -424,6 +424,10 @@ struct ftrace_likely_data {
> # define randomized_struct_fields_end
> #endif
>
> +#ifndef __no_kstack_erase
> +# define __no_kstack_erase
> +#endif
> +
> #ifndef __noscs
> # define __noscs
> #endif
> 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")
> --
> 2.34.1
>
