linux-kernel - Re: [patch 00/38] x86/retbleed: Call depth tracking mitigation

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Date:   Thu, 21 Jul 2022 13:22:12 -0700
From:   Joao Moreira <joao@...rdrivepizza.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        "Cooper, Andrew" <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>,
        "Moreira, Joao" <joao.moreira@...el.com>,
        "Nuzman, Joseph" <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Gross, Jurgen" <jgross@...e.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Peter Collingbourne <pcc@...gle.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [patch 00/38] x86/retbleed: Call depth tracking mitigation

> Ok. I don't know the context, but I was thinking along the lines of
> the same hash value perhaps being used multiple times because it has
> the same function type.  Then using the "addl" trick means that the
> hash value in %r10 will be changing and cannot be re-used.

Fwiiw, even if %r10 value was not being destroyed by the "addl", the 
call right after the check implies that you cannot trust the contents of 
%r10 anymore (it may have been messed up within the called function).