linux-kernel - Re: [PATCH 1/3] kbuild: provide reasonable defaults for tool coverage

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Date: Tue, 28 May 2024 13:35:10 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Masahiro Yamada" <masahiroy@...nel.org>, linux-kbuild@...r.kernel.org
Cc: Linux-Arch <linux-arch@...r.kernel.org>, linux-kernel@...r.kernel.org,
 "Kees Cook" <keescook@...omium.org>
Subject: Re: [PATCH 1/3] kbuild: provide reasonable defaults for tool coverage

On Mon, May 6, 2024, at 15:35, Masahiro Yamada wrote:
> The objtool, sanitizers (KASAN, UBSAN, etc.), and profilers (GCOV, etc.)
> are intended for kernel space objects. To exclude objects from their
> coverage, you need to set variables such as OBJECT_FILES_NON_STNDARD=y,
> KASAN_SANITIZE=n, etc.
>
> For instance, the following are not kernel objects, and therefore should
> opt out of coverage:
>
>   - vDSO
>   - purgatory
>   - bootloader (arch/*/boot/)
>
> Kbuild can detect these cases without relying on such variables because
> objects not directly linked to vmlinux or modules are considered
> "non-standard objects".
>
> Detecting objects linked to vmlinux or modules is straightforward:
>
>   - objects added to obj-y are linked to vmlinux
>   - objects added to lib-y are linked to vmlinux
>   - objects added to obj-m are linked to modules
>

I noticed new randconfig build warnings and bisected them
down to this patch:

warning: unsafe memchr_inv() usage lacked '__read_overflow' symbol in lib/test_fortify/read_overflow-memchr_inv.c
warning: unsafe memchr() usage lacked '__read_overflow' warning in lib/test_fortify/read_overflow-memchr.c
warning: unsafe memscan() usage lacked '__read_overflow' symbol in lib/test_fortify/read_overflow-memscan.c
warning: unsafe memcmp() usage lacked '__read_overflow' warning in lib/test_fortify/read_overflow-memcmp.c
warning: unsafe memcpy() usage lacked '__read_overflow2' symbol in lib/test_fortify/read_overflow2-memcpy.c
warning: unsafe memcmp() usage lacked '__read_overflow2' warning in lib/test_fortify/read_overflow2-memcmp.c
warning: unsafe memmove() usage lacked '__read_overflow2' symbol in lib/test_fortify/read_overflow2-memmove.c
warning: unsafe memcpy() usage lacked '__read_overflow2_field' symbol in lib/test_fortify/read_overflow2_field-memcpy.c
warning: unsafe memmove() usage lacked '__read_overflow2_field' symbol in lib/test_fortify/read_overflow2_field-memmove.c
warning: unsafe memcpy() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-memcpy.c
warning: unsafe memmove() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-memmove.c
warning: unsafe memset() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-memset.c
warning: unsafe strcpy() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-strcpy-lit.c
warning: unsafe strcpy() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-strcpy.c
warning: unsafe strncpy() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-strncpy-src.c
warning: unsafe strncpy() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-strncpy.c
warning: unsafe strscpy() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-strscpy.c
warning: unsafe memcpy() usage lacked '__write_overflow_field' symbol in lib/test_fortify/write_overflow_field-memcpy.c
warning: unsafe memmove() usage lacked '__write_overflow_field' symbol in lib/test_fortify/write_overflow_field-memmove.c
warning: unsafe memset() usage lacked '__write_overflow_field' symbol in lib/test_fortify/write_overflow_field-memset.c

I don't understand the nature of this warning, but I see
that your patch ended up dropping -fsanitize=kernel-address
from the compiler flags because the lib/test_fortify/*.c files
don't match the $(is-kernel-object) rule. Adding back
-fsanitize=kernel-address shuts up these warnings.

I've applied a local workaround in my randconfig tree

diff --git a/lib/Makefile b/lib/Makefile
index ddcb76b294b5..d7b8fab64068 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -425,5 +425,7 @@ $(obj)/$(TEST_FORTIFY_LOG): $(addprefix $(obj)/, $(TEST_FORTIFY_LOGS)) FORCE
 
 # Fake dependency to trigger the fortify tests.
 ifeq ($(CONFIG_FORTIFY_SOURCE),y)
+ifndef CONFIG_KASAN
 $(obj)/string.o: $(obj)/$(TEST_FORTIFY_LOG)
+endif
 endif


which I don't think we want upstream. Can you and Kees come
up with a proper fix instead?

     Arnd