This is a note to let you know that I've just added the patch titled

lkdtm: turn off kcov for lkdtm_rodata_do_nothing:

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: lkdtm-turn-off-kcov-for-lkdtm_rodata_do_nothing.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Sun Mar 18 16:55:33 CET 2018

From: Arnd Bergmann arnd@arndb.de Date: Tue, 28 Mar 2017 11:57:27 +0200 Subject: lkdtm: turn off kcov for lkdtm_rodata_do_nothing:

From: Arnd Bergmann arnd@arndb.de

[ Upstream commit 7064dc7fc13b2994d33ae540ffb7a3a05ac463bf ]

I ran into a link error on ARM64 for lkdtm_rodata_do_nothing:

drivers/misc/built-in.o: In function `lkdtm_rodata_do_nothing': :(.rodata+0x68c8): relocation truncated to fit: R_AARCH64_CALL26 against symbol `__sanitizer_cov_trace_pc' defined in .text section in kernel/built-in.o

I did not analyze this further, but my theory is that we would need a trampoline to call __sanitizer_cov_trace_pc(), but the linker (correctly) only adds trampolines for callers in executable sections.

Disabling KCOV for this one file avoids the build failure with no other practical downsides I can think of.

The problem can only happen on kernels that contain both kcov and lkdtm, so if we want to backport this, it should be in the earliest version that has both (v4.8).

Fixes: 5c9a8750a640 ("kernel: add kcov code coverage") Fixes: 9a49a528dcf3 ("lkdtm: add function for testing .rodata section") Signed-off-by: Arnd Bergmann arnd@arndb.de Acked-by: Dmitry Vyukov dvyukov@google.com Acked-by: Kees Cook keescook@chromium.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/misc/Makefile | 2 ++ 1 file changed, 2 insertions(+)

--- a/drivers/misc/Makefile +++ b/drivers/misc/Makefile @@ -61,6 +61,8 @@ lkdtm-$(CONFIG_LKDTM) += lkdtm_perms.o lkdtm-$(CONFIG_LKDTM) += lkdtm_rodata_objcopy.o lkdtm-$(CONFIG_LKDTM) += lkdtm_usercopy.o

+KCOV_INSTRUMENT_lkdtm_rodata.o := n + OBJCOPYFLAGS := OBJCOPYFLAGS_lkdtm_rodata_objcopy.o := \ --set-section-flags .text=alloc,readonly \

Patches currently in stable-queue which might be from arnd@arndb.de are

queue-4.9/lkdtm-turn-off-kcov-for-lkdtm_rodata_do_nothing.patch queue-4.9/soc-tegra-fix-link-errors-with-pmc-disabled.patch