Re: [PATCH v1 1/1] x86/kernel: Increase kcov coverage under arch/x86/kernel folder

[Pengfei Xu]

Hi Dmitry,

On 2023-07-05 at 06:28:10 +0200, Dmitry Vyukov wrote:
> On Tue, 4 Jul 2023 at 10:58, Pengfei Xu <pengfei.xu@xxxxxxxxx> wrote:
> >
> > Currently kcov instrument is disabled for object files under arch/x86/kernel
> > folder.
> > For object files under arch/x86/kernel, actually just disabling the kcov
> > instrument of files:"head32.o or head64.o and sev.o" could achieve
> > successful booting and provide kcov coverage for object files that do not
> > disable kcov instrument.
> > The additional kcov coverage collected from arch/x86/kernel folder helps
> > kernel fuzzing efforts to find bugs.
> >
> > Link to related improvement discussion is below:
> > https://groups.google.com/g/syzkaller/c/Dsl-RYGCqs8/m/x-tfpTyFBAAJ
> > Related ticket is as follow:
> > https://bugzilla.kernel.org/show_bug.cgi?id=198443
> >
> > Signed-off-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
> 
> Reviewed-and-tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> 
> I've run a local syzkaller instance with this and I don't see any
> additional kernel bugs caused by this and I see coverage in
> arch/x86/kernel/* now, in particular, dumpstack.c, perf_regs.c,
> signal.c.

Thanks for your tag! Yes, it can cover more code in arch/x86/kernel/.

Best Regards,
Thanks!

> 
> 
> > ---
> >  arch/x86/kernel/Makefile | 9 ++++-----
> >  1 file changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> > index 4070a01c11b7..00df34c263cc 100644
> > --- a/arch/x86/kernel/Makefile
> > +++ b/arch/x86/kernel/Makefile
> > @@ -33,11 +33,10 @@ KCSAN_SANITIZE := n
> >  KMSAN_SANITIZE_head$(BITS).o                           := n
> >  KMSAN_SANITIZE_nmi.o                                   := n
> >
> > -# If instrumentation of this dir is enabled, boot hangs during first second.
> > -# Probably could be more selective here, but note that files related to irqs,
> > -# boot, dumpstack/stacktrace, etc are either non-interesting or can lead to
> > -# non-deterministic coverage.
> > -KCOV_INSTRUMENT                := n
> > +# If instrumentation of the following files is enabled, boot hangs during
> > +# first second.
> > +KCOV_INSTRUMENT_head$(BITS).o                          := n
> > +KCOV_INSTRUMENT_sev.o                                  := n
> >
> >  CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace
> >
> > --
> > 2.31.1
> >