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Message-ID: <fce9898e392f42a0830892a1735deb3e@AcuMS.aculab.com>
Date: Sat, 11 Dec 2021 17:23:26 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Peter Collingbourne' <pcc@...gle.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
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Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
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"Thomas Gleixner" <tglx@...utronix.de>,
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CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
Evgenii Stepanov <eugenis@...gle.com>
Subject: RE: [PATCH v4 0/7] kernel: introduce uaccess logging
From: Peter Collingbourne
> Sent: 09 December 2021 22:16
>
> This patch series introduces a kernel feature known as uaccess
> logging, which allows userspace programs to be made aware of the
> address and size of uaccesses performed by the kernel during
> the servicing of a syscall. More details on the motivation
> for and interface to this feature are available in the file
> Documentation/admin-guide/uaccess-logging.rst added by the final
> patch in the series.
How does this work when get_user() and put_user() are used to
do optimised copies?
While adding checks to copy_to/from_user() is going to have
a measurable performance impact - even if nothing is done,
adding them to get/put_user() (and friends) is going to
make some hot paths really slow.
So maybe you could add it so KASAN test kernels, but you can't
sensibly enable it on a production kernel.
Now, it might be that you could semi-sensibly log 'data' transfers.
But have you actually looked at all the transfers that happen
for something like sendmsg().
The 'user copy hardening' code already has a significant impact
on that code (in many places).
David
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