On Tue, Mar 28, 2017 at 09:57:34AM -0700, Kees Cook wrote: > On Tue, Mar 28, 2017 at 3:00 AM, Dmitry Vyukov <[email protected]> wrote: > > On Tue, Mar 28, 2017 at 11:57 AM, Arnd Bergmann <[email protected]> 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 <[email protected]> > >> Cc: Kees Cook <[email protected]> > >> Fixes: 5c9a8750a640 ("kernel: add kcov code coverage") > >> Fixes: 9a49a528dcf3 ("lkdtm: add function for testing .rodata section") > >> Signed-off-by: Arnd Bergmann <[email protected]> > >> --- > >> 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 <[email protected]> > > Acked-by: Kees Cook <[email protected]> > > Greg, can you please add this to the drivers/misc tree when you get a chance?
Will do. thanks, greg k-h
