linux-kernel - Re: [PATCH 2/4] kmsan: disable ftrace in kmsan core code

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Date:   Wed, 8 Feb 2023 18:00:38 +0100
From:   Marco Elver <elver@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Arnd Bergmann <arnd@...db.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] kmsan: disable ftrace in kmsan core code

On Wed, 8 Feb 2023 at 17:40, Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> objtool warns about some suspicous code inside of kmsan:
>
> vmlinux.o: warning: objtool: __msan_metadata_ptr_for_load_n+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_metadata_ptr_for_store_n+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_metadata_ptr_for_load_1+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_metadata_ptr_for_store_1+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_metadata_ptr_for_load_2+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_metadata_ptr_for_store_2+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_metadata_ptr_for_load_4+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_metadata_ptr_for_store_4+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_metadata_ptr_for_load_8+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_metadata_ptr_for_store_8+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_instrument_asm_store+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_chain_origin+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_poison_alloca+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_warning+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: __msan_get_context_state+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: kmsan_copy_to_user+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: kmsan_unpoison_memory+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: kmsan_unpoison_entry_regs+0x4: call to __fentry__() with UACCESS enabled
> vmlinux.o: warning: objtool: kmsan_report+0x4: call to __fentry__() with UACCESS enabled
>
> Similar code already exists in kasan, which avoids this by skipping
> ftrace annotations, so do the same thing here.
>
> Fixes: f80be4571b19 ("kmsan: add KMSAN runtime core")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  mm/kmsan/Makefile | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/mm/kmsan/Makefile b/mm/kmsan/Makefile
> index 98eab2856626..389fd767a11f 100644
> --- a/mm/kmsan/Makefile
> +++ b/mm/kmsan/Makefile
> @@ -16,6 +16,14 @@ CC_FLAGS_KMSAN_RUNTIME += -DDISABLE_BRANCH_PROFILING
>
>  CFLAGS_REMOVE.o = $(CC_FLAGS_FTRACE)

That means this CFLAGS_REMOVE.o didn't work, right? Can it be removed?

> +# Disable ftrace to avoid recursion.
> +CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
> +CFLAGS_REMOVE_hooks.o = $(CC_FLAGS_FTRACE)
> +CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE)
> +CFLAGS_REMOVE_instrumentation.o = $(CC_FLAGS_FTRACE)
> +CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
> +CFLAGS_REMOVE_shadow.o = $(CC_FLAGS_FTRACE)
> +
>  CFLAGS_core.o := $(CC_FLAGS_KMSAN_RUNTIME)
>  CFLAGS_hooks.o := $(CC_FLAGS_KMSAN_RUNTIME)
>  CFLAGS_init.o := $(CC_FLAGS_KMSAN_RUNTIME)
> --
> 2.39.1
>