linux-kernel - Re: [PATCH] add param that allows bootline control of hardened usercopy

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Date:   Tue, 26 Jun 2018 11:48:31 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     crecklin@...hat.com, Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm@...r.kernel.org
Subject: Re: [PATCH] add param that allows bootline control of hardened
 usercopy

Hi,

On Mon, 25 Jun 2018 11:21:38 -0700 Kees Cook <keescook@...omium.org> wrote:
> On Mon, Jun 25, 2018 at 8:08 AM, Chris von Recklinghausen
> <crecklin@...hat.com> wrote:
> > Enabling HARDENED_USER_COPY causes measurable regressions in the
> > networking performances, up to 8% under UDP flood.
> 
> Which function is "hot"? i.e. which copy*user() is taking up the time?
> Do you have a workload that at can be used to reproduce the problem?

I'm running an a small packet UDP flood using pktgen vs. an host b2b
connected. On the receiver side the UDP packets are processed by a
simple user space process that just read and drop them:

https://github.com/netoptimizer/network-testing/blob/master/src/udp_sink.c

Not very useful from a functional PoV, it helps mostly pin-pointing
bottle-neck in the networking stack.

When running a kernel with CONFIG_HARDENED_USERCOPY=y, I see a 5-8%
regression in the receive tput, compared to the same kernel without
such option.

With CONFIG_HARDENED_USERCOPY=y, perf shows ~6% of CPU time spent
cumulatively in __check_object_size (~4%) and __virt_addr_valid (~2%).

Cheers,

Paolo