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 <[email protected]>
---
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
On Tue, 4 Jul 2023 at 10:58, Pengfei Xu <[email protected]> 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 <[email protected]>
Reviewed-and-tested-by: Dmitry Vyukov <[email protected]>
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.
> ---
> 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
>
Hi Dmitry,
On 2023-07-05 at 06:28:10 +0200, Dmitry Vyukov wrote:
> On Tue, 4 Jul 2023 at 10:58, Pengfei Xu <[email protected]> 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 <[email protected]>
>
> Reviewed-and-tested-by: Dmitry Vyukov <[email protected]>
>
> 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
> >