linux-kernel - Re: [GIT PULL] execve updates for v6.8-rc1

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Message-ID: <CAHk-=wgnLA7Jhjiuz8W76PRyQheLCkNS__=D1onenqbhpiXsVQ@mail.gmail.com>
Date: Mon, 8 Jan 2024 17:53:51 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Kees Cook <kees@...nel.org>
Cc: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org, 
	Alexey Dobriyan <adobriyan@...il.com>, Josh Triplett <josh@...htriplett.org>
Subject: Re: [GIT PULL] execve updates for v6.8-rc1

On Mon, 8 Jan 2024 at 17:48, Kees Cook <kees@...nel.org> wrote:
>
> This was exactly the feedback I had originally and wrote almost what you suggest:
>
> https://lore.kernel.org/lkml/202209161637.9EDAF6B18@keescook/
>
> But the perf testing of my proposed "look it up once" patch showed a
> net loss to the successful execs which no one could explain. In the
> end we went with the original proposal.

Basing things one one random benchmark which must clearly have some
very particular cache effects or something is not ok.

End result: I'm not taking a random "look up filename twice because we
can't understand what is going on".

Because I *guarantee* that we can trivially write another benchmark
that shows that looking up the pathname twice is worse.

                Linus