Messages in this thread | | | From | Kees Cook <> | Date | Tue, 28 Mar 2017 09:57:34 -0700 | Subject | Re: [PATCH] lkdtm: turn off kcov for lkdtm_rodata_do_nothing: |
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On Tue, Mar 28, 2017 at 3:00 AM, Dmitry Vyukov <dvyukov@google.com> wrote: > On Tue, Mar 28, 2017 at 11:57 AM, Arnd Bergmann <arnd@arndb.de> wrote: >> 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.
Yup, this function should be inherently uncallable (which is what lkdtm is testing), so it makes sense to turn off kcov for it.
>> >> 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). >> >> Cc: Dmitry Vyukov <dvyukov@google.com> >> Cc: Kees Cook <keescook@chromium.org> >> Fixes: 5c9a8750a640 ("kernel: add kcov code coverage") >> Fixes: 9a49a528dcf3 ("lkdtm: add function for testing .rodata section") >> Signed-off-by: Arnd Bergmann <arnd@arndb.de> >> --- >> drivers/misc/Makefile | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile >> index 4925ea8e1952..7a321047bfbe 100644 >> --- a/drivers/misc/Makefile >> +++ b/drivers/misc/Makefile >> @@ -63,6 +63,8 @@ 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 \ >> -- >> 2.9.0 > > > Acked-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Greg, can you please add this to the drivers/misc tree when you get a chance?
Thanks!
-Kees
-- Kees Cook Pixel Security
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