linux-kernel - RE: [PATCH RFC 2/8] arm64: stacktrace: Add arch_within_stack

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Date:   Wed, 20 Apr 2022 07:32:01 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'He Zhe' <zhe.he@...driver.com>, Kees Cook <keescook@...omium.org>
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Subject: RE: [PATCH RFC 2/8] arm64: stacktrace: Add arch_within_stack_frames

> > Thanks for doing this implementation! One reason usercopy hardening
> > didn't persue doing a "full" stacktrace was because it seemed relatively
> > expensive. Did you do any usercopy-heavily workload testing to see if
> > there was a noticeable performance impact?

Look at anything that uses sendmsg().
It is noticeably more expensive than sendto().
All the extra copy_from_user() cause measurable slow slowdowns.
Using __copy_from_user()(to avoid 'hardending') in the socket code
and when reading the iov[] gives a measurable improvement.

	David

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