linux-kernel - Re: [PATCH v2 37/59] x86/putuser: Provide room for padding

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YxI3Zf5drSHAkBL3@hirez.programming.kicks-ass.net>
Date:   Fri, 2 Sep 2022 19:03:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Johannes Wikner <kwikner@...z.ch>,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
        Joao Moreira <joao.moreira@...el.com>,
        Joseph Nuzman <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v2 37/59] x86/putuser: Provide room for padding

On Fri, Sep 02, 2022 at 09:43:45AM -0700, Linus Torvalds wrote:
> So I don't hate this patch and it's probably good for consistency, but
> I really think that the retbleed tracking could perhaps be improved to
> let this be all unnecessary.
> 
> The whole return stack depth counting is already not 100% exact, and I
> think we could just make the rule be that we don't track leaf
> functions.
> 
> Why? It's just a off-by-one in the already not exact tracking. And -
> perhaps equally importantly - leaf functions are very very common
> dynamically, and I suspect it's trivial to see them.
> 
> Yes, yes, you could make objtool even smarter and actually do some
> kind of function flow graph thing (and I think some people were
> talking about that with the whole ret counting long long ago), but the
> leaf function thing is the really simple low-hanging fruit case of
> that.

So I did the leaf thing a few weeks ago, and at the time the perf gains
where not worth the complexity.

I can try again :-)