On Tue, Sep 08, 2020 at 11:39:11AM +0200, Marco Elver wrote: > On Sun, 6 Sep 2020 at 00:23, Arvind Sankar <nived...@alum.mit.edu> wrote: > > > > String functions can be useful in early boot, but using instrumented > > versions can be problematic: eg on x86, some of the early boot code is > > executing out of an identity mapping rather than the kernel virtual > > addresses. Accessing any global variables at this point will lead to a > > crash. > > > > Tracing and KCOV are already disabled, and CONFIG_AMD_MEM_ENCRYPT will > > additionally disable KASAN and stack protector. > > > > Additionally disable GCOV, UBSAN, KCSAN, STACKLEAK_PLUGIN and branch > > profiling, and make it unconditional to allow safe use of string > > functions. > > > > Signed-off-by: Arvind Sankar <nived...@alum.mit.edu> > > --- > > lib/Makefile | 11 +++++++---- > > 1 file changed, 7 insertions(+), 4 deletions(-) > > > > diff --git a/lib/Makefile b/lib/Makefile > > index a4a4c6864f51..5e421769bbc6 100644 > > --- a/lib/Makefile > > +++ b/lib/Makefile > > @@ -8,7 +8,6 @@ ccflags-remove-$(CONFIG_FUNCTION_TRACER) += > > $(CC_FLAGS_FTRACE) > > # These files are disabled because they produce lots of non-interesting > > and/or > > # flaky coverage that is not a function of syscall inputs. For example, > > # rbtree can be global and individual rotations don't correlate with > > inputs. > > -KCOV_INSTRUMENT_string.o := n > > KCOV_INSTRUMENT_rbtree.o := n > > KCOV_INSTRUMENT_list_debug.o := n > > KCOV_INSTRUMENT_debugobjects.o := n > > @@ -20,12 +19,16 @@ KCOV_INSTRUMENT_fault-inject.o := n > > # them into calls to themselves. > > CFLAGS_string.o := -ffreestanding > > > > -# Early boot use of cmdline, don't instrument it > > -ifdef CONFIG_AMD_MEM_ENCRYPT > > +# Early boot use of string functions, disable instrumentation > > +GCOV_PROFILE_string.o := n > > +KCOV_INSTRUMENT_string.o := n > > KASAN_SANITIZE_string.o := n > > +UBSAN_SANITIZE_string.o := n > > +KCSAN_SANITIZE_string.o := n > > Ouch. > > We have found manifestations of bugs in lib/string.c functions, e.g.: > > https://groups.google.com/forum/#!msg/syzkaller-bugs/atbKWcFqE9s/x7AtoVoBAgAJ > > https://groups.google.com/forum/#!msg/syzkaller-bugs/iGBUm-FDhkM/chl05uEgBAAJ > > Is there any way this can be avoided?
Agreed: I would like to keep this instrumentation; it's a common place to find bugs, security issues, etc. -- Kees Cook
