[PATCH] vmlinux.lds.h: Define SANTIZER_DISCARDS with CONFIG_GCOV_KERNEL=y

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Nathan Chancellor

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Jan 29, 2021, 3:11:32 PMJan 29
to Arnd Bergmann, Kees Cook, Nick Desaulniers, linux-...@vger.kernel.org, clang-bu...@googlegroups.com, Nathan Chancellor, kernel test robot
clang produces .eh_frame sections when CONFIG_GCOV_KERNEL is enabled,
even when -fno-asynchronous-unwind-tables is in KBUILD_CFLAGS:

$ make CC=clang vmlinux
...
ld: warning: orphan section `.eh_frame' from `init/main.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/version.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/do_mounts.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/do_mounts_initrd.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/initramfs.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/calibrate.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/init_task.o' being placed in section `.eh_frame'
...

$ rg "GCOV_KERNEL|GCOV_PROFILE_ALL" .config
CONFIG_GCOV_KERNEL=y
CONFIG_ARCH_HAS_GCOV_PROFILE_ALL=y
CONFIG_GCOV_PROFILE_ALL=y

This was already handled for a couple of other options in
commit d812db78288d ("vmlinux.lds.h: Avoid KASAN and KCSAN's unwanted
sections") and there is an open LLVM bug for this issue. Take advantage
of that section for this config as well so that there are no more orphan
warnings.

Link: https://bugs.llvm.org/show_bug.cgi?id=46478
Link: https://github.com/ClangBuiltLinux/linux/issues/1069
Reported-by: kernel test robot <l...@intel.com>
Signed-off-by: Nathan Chancellor <nat...@kernel.org>
---
include/asm-generic/vmlinux.lds.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b2b3d81b1535..f753fd449436 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -988,12 +988,13 @@
#endif

/*
- * Clang's -fsanitize=kernel-address and -fsanitize=thread produce
+ * Clang's -fsanitize=kernel-address, -fsanitize=thread,
+ * and -fprofile-arcs -ftest-coverage produce unwanted
* unwanted sections (.eh_frame and .init_array.*), but
* CONFIG_CONSTRUCTORS wants to keep any .init_array.* sections.
* https://bugs.llvm.org/show_bug.cgi?id=46478
*/
-#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN)
+#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN) || defined(CONFIG_GCOV_KERNEL)
# ifdef CONFIG_CONSTRUCTORS
# define SANITIZER_DISCARDS \
*(.eh_frame)

base-commit: bec4c2968fce2f44ce62d05288a633cd99a722eb
--
2.30.0

Nick Desaulniers

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Jan 29, 2021, 3:18:40 PMJan 29
to Nathan Chancellor, Arnd Bergmann, Kees Cook, LKML, clang-built-linux, kernel test robot, Fangrui Song
Reviewed-by: Nick Desaulniers <ndesau...@google.com>

I suspect we're going to need to add module level attributes in LLVM
IR for these options, then check those when synthesizing new function
definitions within LLVM. At least we'll be able to point to this file
and say "hey, this is a general problem in LLVM, and here are 3
specific cases now where it's a problem." Not a large problem, but
would help us save some bytes in the final object. LLVM is not
producing data in this section for all code, just these synthesized
routines.
--
Thanks,
~Nick Desaulniers

Fangrui Song

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Jan 29, 2021, 4:27:23 PMJan 29
to Nick Desaulniers, Nathan Chancellor, Arnd Bergmann, Kees Cook, LKML, clang-built-linux, kernel test robot
Maybe. There are also a long list of security features which may impose
additional requirements. Adding a module flag metadata for each such
feature will be a long battle. For .eh_frame, I think it is
important/generic enough and can benefit other applications that
deserves special handling (and I can look into it). For .init_array, I
am not too sure....
Drop -ftest-coverage. -ftest-coverage just produces .gcno and does not
affect code generation.

Reviewed-by: Fangrui Song <mas...@google.com>

Nathan Chancellor

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Jan 29, 2021, 7:27:16 PMJan 29
to Arnd Bergmann, Kees Cook, Nick Desaulniers, linux-...@vger.kernel.org, clang-bu...@googlegroups.com, Nathan Chancellor, kernel test robot, Fangrui Song
clang produces .eh_frame sections when CONFIG_GCOV_KERNEL is enabled,
even when -fno-asynchronous-unwind-tables is in KBUILD_CFLAGS:

$ make CC=clang vmlinux
...
ld: warning: orphan section `.eh_frame' from `init/main.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/version.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/do_mounts.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/do_mounts_initrd.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/initramfs.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/calibrate.o' being placed in section `.eh_frame'
ld: warning: orphan section `.eh_frame' from `init/init_task.o' being placed in section `.eh_frame'
...

$ rg "GCOV_KERNEL|GCOV_PROFILE_ALL" .config
CONFIG_GCOV_KERNEL=y
CONFIG_ARCH_HAS_GCOV_PROFILE_ALL=y
CONFIG_GCOV_PROFILE_ALL=y

This was already handled for a couple of other options in
commit d812db78288d ("vmlinux.lds.h: Avoid KASAN and KCSAN's unwanted
sections") and there is an open LLVM bug for this issue. Take advantage
of that section for this config as well so that there are no more orphan
warnings.

Link: https://bugs.llvm.org/show_bug.cgi?id=46478
Link: https://github.com/ClangBuiltLinux/linux/issues/1069
Reported-by: kernel test robot <l...@intel.com>
Reviewed-by: Fangrui Song <mas...@google.com>
Reviewed-by: Nick Desaulniers <ndesau...@google.com>
Signed-off-by: Nathan Chancellor <nat...@kernel.org>
---

v1 -> v2:

* Keep configs and flag names alphabetized.

* Drop mention of -ftest-coverage since it does not cause this issue per
Fangrui.

* Pick up review tags from Fangrui and Nick.

include/asm-generic/vmlinux.lds.h | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b2b3d81b1535..0e6c5da667a7 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -988,12 +988,13 @@
#endif

/*
- * Clang's -fsanitize=kernel-address and -fsanitize=thread produce
- * unwanted sections (.eh_frame and .init_array.*), but
- * CONFIG_CONSTRUCTORS wants to keep any .init_array.* sections.
+ * Clang's -fprofile-arcs, -fsanitize=kernel-address, and
+ * -fsanitize=thread produce unwanted unwanted sections
+ * (.eh_frame and .init_array.*), but CONFIG_CONSTRUCTORS
+ * wants to keep any .init_array.* sections.
* https://bugs.llvm.org/show_bug.cgi?id=46478
*/
-#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN)
+#if defined(CONFIG_GCOV_KERNEL) || defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN)

Sedat Dilek

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Jan 29, 2021, 7:39:42 PMJan 29
to Nathan Chancellor, Arnd Bergmann, Kees Cook, Nick Desaulniers, linux-...@vger.kernel.org, Clang-Built-Linux ML, kernel test robot, Fangrui Song
Typo: double "unwanted".

- Sedat -

> + * (.eh_frame and .init_array.*), but CONFIG_CONSTRUCTORS
> + * wants to keep any .init_array.* sections.
> * https://bugs.llvm.org/show_bug.cgi?id=46478
> */
> -#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN)
> +#if defined(CONFIG_GCOV_KERNEL) || defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN)
> # ifdef CONFIG_CONSTRUCTORS
> # define SANITIZER_DISCARDS \
> *(.eh_frame)
>
> base-commit: bec4c2968fce2f44ce62d05288a633cd99a722eb
> --
> 2.30.0
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
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Nathan Chancellor

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Jan 29, 2021, 7:47:43 PMJan 29
to Arnd Bergmann, Kees Cook, Nick Desaulniers, linux-...@vger.kernel.org, clang-bu...@googlegroups.com, Nathan Chancellor, kernel test robot, Fangrui Song
v2 -> v3:

* Fix double "unwanted" in comment section per Sedat.

v1 -> v2:

* Keep configs and flag names alphabetized.

* Drop mention of -ftest-coverage since it does not cause this issue per
Fangrui.

* Pick up review tags from Fangrui and Nick.

include/asm-generic/vmlinux.lds.h | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b2b3d81b1535..b61b537177fb 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -988,12 +988,13 @@
#endif

/*
- * Clang's -fsanitize=kernel-address and -fsanitize=thread produce
- * unwanted sections (.eh_frame and .init_array.*), but
- * CONFIG_CONSTRUCTORS wants to keep any .init_array.* sections.
+ * Clang's -fprofile-arcs, -fsanitize=kernel-address, and
+ * -fsanitize=thread produce unwanted sections (.eh_frame
+ * and .init_array.*), but CONFIG_CONSTRUCTORS wants to
+ * keep any .init_array.* sections.

Nathan Chancellor

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Feb 25, 2021, 2:28:27 PMFeb 25
to Arnd Bergmann, Kees Cook, Andrew Morton, Nick Desaulniers, linux-...@vger.kernel.org, clang-bu...@googlegroups.com, kernel test robot, Fangrui Song
Andrew, Arnd, or Kees:

Would one of you be able to pick this up and get it to Linus? I think
the 0day bot just tripped over this again:

https://lists.01.org/hyperkitty/list/kbuil...@lists.01.org/message/BXBY7OPVMOCCUZSCFEZXI7RG65RJWJ52/
https://lists.01.org/hyperkitty/list/kbuil...@lists.01.org/message/QF62LWM6YSNWWNOM7AXYK4734AKH2SVT/

Cheers,
Nathan

Kees Cook

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Feb 25, 2021, 4:19:23 PMFeb 25
to Arnd Bergmann, Nathan Chancellor, Kees Cook, kernel test robot, Nick Desaulniers, linux-...@vger.kernel.org, clang-bu...@googlegroups.com, Fangrui Song
On Fri, 29 Jan 2021 17:46:51 -0700, Nathan Chancellor wrote:
> clang produces .eh_frame sections when CONFIG_GCOV_KERNEL is enabled,
> even when -fno-asynchronous-unwind-tables is in KBUILD_CFLAGS:
>
> $ make CC=clang vmlinux
> ...
> ld: warning: orphan section `.eh_frame' from `init/main.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/version.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/do_mounts.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/do_mounts_initrd.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/initramfs.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/calibrate.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/init_task.o' being placed in section `.eh_frame'
> ...
>
> [...]

Applied to kspp/linker/orphans, thanks!

[1/1] vmlinux.lds.h: Define SANTIZER_DISCARDS with CONFIG_GCOV_KERNEL=y
https://git.kernel.org/kees/c/f5b6a74d9c08

--
Kees Cook

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