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Message-ID: <201911262134.ED9E60965@keescook>
Date: Tue, 26 Nov 2019 21:42:11 -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 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://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? 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).
I think kasan and ubsan should be reworked to use the common warn
infrastructure, and at the very least, ubsan needs this:
diff --git a/lib/ubsan.c b/lib/ubsan.c
index e7d31735950d..a2535a62c9af 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -160,6 +160,17 @@ static void ubsan_epilogue(unsigned long *flags)
"========================================\n");
spin_unlock_irqrestore(&report_lock, *flags);
current->in_ubsan--;
+
+ if (panic_on_warn) {
+ /*
+ * This thread may hit another WARN() in the panic path.
+ * Resetting this prevents additional WARN() from panicking the
+ * system on this thread. Other threads are blocked by the
+ * panic_mutex in panic().
+ */
+ panic_on_warn = 0;
+ panic("panic_on_warn set ...\n");
+ }
}
static void handle_overflow(struct overflow_data *data, void *lhs,
> Kees, or anybody else interested, could you provide relevant configs
> that (1) useful for kernel,
As mentioned in the other email (but just to keep the note together with
the other thoughts here) after this series, you'd want:
CONFIG_UBSAN=y
CONFIG_UBSAN_BOUNDS=y
# CONFIG_UBSAN_MISC is not set
> (2) we want 100% cleanliness,
What do you mean here by "cleanliness"? It seems different from (3)
about the test tripping a lot?
> (3) don't
> fire all the time even without fuzzing?
I ran with the bounds checker enabled (and the above patch) under
syzkaller for the weekend and saw 0 bounds checker reports.
> Anything else required to
> enable UBSAN? I don't see anything. syzbot uses gcc 8.something, which
> I assume should be enough (but we can upgrade if necessary).
As mentioned, gcc 8+ should be fine.
--
Kees Cook
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