Date: Wed, 27 Nov 2019 09:59:18 -0800 From: Kees Cook <keescook@...omium.org> To: Dmitry Vyukov <dvyukov@...gle.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Andrey Ryabinin <aryabinin@...tuozzo.com>, Elena Petrova <lenaptr@...gle.com>, Alexander Potapenko <glider@...gle.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Dan Carpenter <dan.carpenter@...cle.com>, "Gustavo A. R. Silva" <gustavo@...eddedor.com>, Arnd Bergmann <arnd@...db.de>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, kasan-dev <kasan-dev@...glegroups.com>, LKML <linux-kernel@...r.kernel.org>, kernel-hardening@...ts.openwall.com, syzkaller <syzkaller@...glegroups.com> Subject: Re: [PATCH v2 0/3] ubsan: Split out bounds checker 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@...gle.com> wrote: > > > > On Wed, Nov 27, 2019 at 6:42 AM Kees Cook <keescook@...omium.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@...omium.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://firstname.lastname@example.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 noticed a few things > > > about the ubsan handlers: they don't use any of the common "warn" > > > infrastructure (neither does kasan from what I can see), and was missing > > > a check for panic_on_warn (kasan has this, but does it incorrectly). > > > > Yes, panic_on_warn we also need. > > > > I will look at the patches again for Acked-by. > > > Acked-by: Dmitry Vyukov <dvyukov@...gle.com> > for the series. Thanks! > > I see you extended the test module, do you have samples of all UBSAN > report types that are triggered by these functions? Is so, please add > them to: > https://github.com/google/syzkaller/tree/master/pkg/report/testdata/linux/report Okay, cool. > with whatever titles they are detected now. Improving titles will then > be the next step, but much simpler with a good collection of tests. > > Will you send the panic_on_want patch as well? Yes; I wanted to make sure it was needed first (which you've confirmed now). I'll likely not send it until next week. -- Kees Cook
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