linux-kernel - RE: [PATCH v3 3/3] x86: usercopy: reimplement arch_within_stack

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Date:   Mon, 9 Apr 2018 13:14:58 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'kpark3469@...il.com'" <kpark3469@...il.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
CC:     "catalin.marinas@....com" <catalin.marinas@....com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "will.deacon@....com" <will.deacon@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "james.morse@....com" <james.morse@....com>,
        "panand@...hat.com" <panand@...hat.com>,
        "keun-o.park@...kmatter.ae" <keun-o.park@...kmatter.ae>,
        "psodagud@...eaurora.org" <psodagud@...eaurora.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 3/3] x86: usercopy: reimplement
 arch_within_stack_frames with unwinder

From: kpark3469@...il.com
> Sent: 09 April 2018 12:59
>
> The old arch_within_stack_frames which used the frame pointer is
> now reimplemented to use frame pointer unwinder apis. So the main
> functionality is same as before.

How much slower does this make the code?
Following stack frames using %bp is reasonably quick.
I can't imagine some of the other unwinder APIs being any where
near that fast.
While fine for fault tracebacks, using them during usercopy
is likely to have measurable performance impact.

	David