Re: [PATCH v4 00/17] khwasan: kernel hardware assisted address sanitizer

[Vishwath Mohan <vishwath@google.com>]

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On Wed, Jun 27, 2018 at 5:04 PM Kostya Serebryany <kcc@google.com> wrote:

> On Wed, Jun 27, 2018 at 4:08 PM Andrew Morton <akpm@linux-foundation.org>
> wrote:
> >
> > On Tue, 26 Jun 2018 15:15:10 +0200 Andrey Konovalov <
> andreyknvl@google.com> wrote:
> >
> > > This patchset adds a new mode to KASAN [1], which is called KHWASAN
> > > (Kernel HardWare assisted Address SANitizer).
> > >
> > > The plan is to implement HWASan [2] for the kernel with the incentive,
> > > that it's going to have comparable to KASAN performance, but in the
> same
> > > time consume much less memory, trading that off for somewhat imprecise
> > > bug detection and being supported only for arm64.
> >
> > Why do we consider this to be a worthwhile change?
> >
> > Is KASAN's memory consumption actually a significant problem?  Some
> > data regarding that would be very useful.
>
> On mobile, ASAN's and KASAN's memory usage is a significant problem.
> Not sure if I can find scientific evidence of that.
> CC-ing Vishwath Mohan who deals with KASAN on Android to provide
> anecdotal evidence.
>
Yeah, I can confirm that it's an issue. Like Kostya mentioned, I don't have
data on-hand, but anecdotally both ASAN and KASAN have proven problematic
to enable for environments that don't tolerate the increased memory
pressure well. This includes,
(a) Low-memory form factors - Wear, TV, Things, lower-tier phones like Go
(c) Connected components like Pixel's visual core
<https://www.blog.google/products/pixel/pixel-visual-core-image-processing-and-machine-learning-pixel-2/>


These are both places I'd love to have a low(er) memory footprint option at
my disposal.


> There are several other benefits too:
> * HWASAN more reliably detects non-linear-buffer-overflows compared to
> ASAN (same for kernel-HWASAN vs kernel-ASAN)
> * Same for detecting use-after-free (since HWASAN doesn't rely on
> quarantine).
> * Much easier to implement stack-use-after-return detection (which
> IIRC KASAN doesn't have yet, because in KASAN it's too hard)
>
> > If it is a large problem then we still have that problem on x86, so the
> > problem remains largely unsolved?
>
> The problem is more significant on mobile devices than on desktop/server.
> I'd love to have [K]HWASAN on x86_64 as well, but it's less trivial since
> x86_64
> doesn't have an analog of aarch64's top-byte-ignore hardware feature.
>
>
> >
> > > ====== Benchmarks
> > >
> > > The following numbers were collected on Odroid C2 board. Both KASAN and
> > > KHWASAN were used in inline instrumentation mode.
> > >
> > > Boot time [1]:
> > > * ~1.7 sec for clean kernel
> > > * ~5.0 sec for KASAN
> > > * ~5.0 sec for KHWASAN
> > >
> > > Slab memory usage after boot [2]:
> > > * ~40 kb for clean kernel
> > > * ~105 kb + 1/8th shadow ~= 118 kb for KASAN
> > > * ~47 kb + 1/16th shadow ~= 50 kb for KHWASAN
> > >
> > > Network performance [3]:
> > > * 8.33 Gbits/sec for clean kernel
> > > * 3.17 Gbits/sec for KASAN
> > > * 2.85 Gbits/sec for KHWASAN
> > >
> > > Note, that KHWASAN (compared to KASAN) doesn't require quarantine.
> > >
> > > [1] Time before the ext4 driver is initialized.
> > > [2] Measured as `cat /proc/meminfo | grep Slab`.
> > > [3] Measured as `iperf -s & iperf -c 127.0.0.1 -t 30`.
> >
> > The above doesn't actually demonstrate the whole point of the
> > patchset: to reduce KASAN's very high memory consumption?
> >
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