Re: [PATCH v2 0/3] ubsan: Split out bounds checker

Dmitry Vyukov
2019-11-28T13:10:37Z

On Wed, Nov 27, 2019 at 6:59 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Wed, Nov 27, 2019 at 10:34:24AM +0100, Dmitry Vyukov wrote:
> > On Wed, Nov 27, 2019 at 7:54 AM Dmitry Vyukov <dvyukov@google.com> wrote:
> > >
> > > On Wed, Nov 27, 2019 at 6:42 AM Kees Cook <keescook@chromium.org> wrote:
> > > >
> > > > On Fri, Nov 22, 2019 at 10:07:29AM +0100, Dmitry Vyukov wrote:
> > > > > On Thu, Nov 21, 2019 at 7:15 PM Kees Cook <keescook@chromium.org> wrote:
> > > > > >
> > > > > > v2:
> > > > > > - clarify Kconfig help text (aryabinin)
> > > > > > - add reviewed-by
> > > > > > - aim series at akpm, which seems to be where ubsan goes through?
> > > > > > v1: https://lore.kernel.org/lkml/20191120010636.27368-1-keescook@chromium.org
> > > > > >
> > > > > > This splits out the bounds checker so it can be individually used. This
> > > > > > is expected to be enabled in Android and hopefully for syzbot. Includes
> > > > > > LKDTM tests for behavioral corner-cases (beyond just the bounds checker).
> > > > > >
> > > > > > -Kees
> > > > >
> > > > > +syzkaller mailing list
> > > > >
> > > > > This is great!
> > > >
> > > > BTW, can I consider this your Acked-by for these patches? :)
> > > >
> > > > > I wanted to enable UBSAN on syzbot for a long time. And it's
> > > > > _probably_ not lots of work. But it was stuck on somebody actually
> > > > > dedicating some time specifically for it.
> > > >
> > > > Do you have a general mechanism to test that syzkaller will actually
> > > > pick up the kernel log splat of a new check?
> > >
> > > Yes. That's one of the most important and critical parts of syzkaller :)
> > > The tests for different types of bugs are here:
> > > https://github.com/google/syzkaller/tree/master/pkg/report/testdata/linux/report
> > >
> > > But have 3 for UBSAN, but they may be old and it would be useful to
> > > have 1 example crash per bug type:
> > >
> > > syzkaller$ grep UBSAN pkg/report/testdata/linux/report/*
> > > pkg/report/testdata/linux/report/40:TITLE: UBSAN: Undefined behaviour
> > > in drivers/usb/core/devio.c:LINE
> > > pkg/report/testdata/linux/report/40:[ 4.556972] UBSAN: Undefined
> > > behaviour in drivers/usb/core/devio.c:1517:25
> > > pkg/report/testdata/linux/report/41:TITLE: UBSAN: Undefined behaviour
> > > in ./arch/x86/include/asm/atomic.h:LINE
> > > pkg/report/testdata/linux/report/41:[ 3.805453] UBSAN: Undefined
> > > behaviour in ./arch/x86/include/asm/atomic.h:156:2
> > > pkg/report/testdata/linux/report/42:TITLE: UBSAN: Undefined behaviour
> > > in kernel/time/hrtimer.c:LINE
> > > pkg/report/testdata/linux/report/42:[ 50.583499] UBSAN: Undefined
> > > behaviour in kernel/time/hrtimer.c:310:16
> > >
> > > One of them is incomplete and is parsed as "corrupted kernel output"
> > > (won't be reported):
> > > https://github.com/google/syzkaller/blob/master/pkg/report/testdata/linux/report/42
> > >
> > > Also I see that report parsing just takes the first line, which
> > > includes file name, which is suboptimal (too long, can't report 2 bugs
> > > in the same file). We seem to converge on "bug-type in function-name"
> > > format.
> > > The thing about bug titles is that it's harder to change them later.
> > > If syzbot already reported 100 bugs and we change titles, it will
> > > start re-reporting the old one after new names and the old ones will
> > > look stale, yet they still relevant, just detected under different
> > > name.
> > > So we also need to get this part right before enabling.
>
> It Sounds like instead of "UBSAN: Undefined behaviour in $file", UBSAN
> should report something like "UBSAN: $behavior in $file"?
>
> e.g.
> 40: UBSAN: bad shift in drivers/usb/core/devio.c:1517:25"
> 41: UBSAN: signed integer overflow in ./arch/x86/include/asm/atomic.h:156:2
>
> I'll add one for the bounds checker.
>
> How are these reports used? (And is there a way to check a live kernel
> crash? i.e. to tell syzkaller "echo ARRAY_BOUNDS >/.../lkdtm..." and
> generate a report?

I've collected the sample and added to syzkaller test base:
https://github.com/google/syzkaller/commit/76357d6f894431c00cc09cfc9e7474701a4b822a

I also filed https://github.com/google/syzkaller/issues/1523 for
enabling UBSAN on syzbot, let's move syzbot-related discussion there.