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

[Kostya Serebryany]

On Wed, Jun 27, 2018 at 4:08 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Tue, 26 Jun 2018 15:15:10 +0200 Andrey Konovalov <andreyknvl@xxxxxxxxxx> 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.

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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