Messages in this thread | ![/](/images/icornerl.gif) | | From | Peter Collingbourne <> | Date | Mon, 13 Dec 2021 11:48:35 -0800 | Subject | Re: [PATCH v4 0/7] kernel: introduce uaccess logging |
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On Sat, Dec 11, 2021 at 9:23 AM David Laight <David.Laight@aculab.com> wrote: > > 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).
Hi David,
Yes, I realised after I sent out my patch (and while writing test cases for it) that it didn't cover get_user()/put_user(). I have a patch under development that will add this coverage. I used it to run my invalid syscall and uname benchmarks and the results were basically the same as without the coverage.
Are you aware of any benchmarks that cover sendmsg()? I can try to look at writing my own if not. I was also planning to write a benchmark that uses getresuid() as this was the simplest syscall that I could find that does multiple put_user() calls.
Peter
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