Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220716230344.239749011@linutronix.de> <87wncauslw.ffs@tglx>
 <87tu7euska.ffs@tglx> <CAHk-=wjpzVRU0Yr_0DJSB_bKHW3_74UucNpJBjxfHPo_R=PYNg@mail.gmail.com>
 <87o7xmup5t.ffs@tglx> <YtXOMPpmx8TcFtOX@worktop.programming.kicks-ass.net>
 <87lesqukm5.ffs@tglx> <2f7f899cb75b79b08b0662ff4d2cb877@overdrivepizza.com>
 <CABCJKudvSv9bAOrDLHki5XPYNJK6=PS-x8v=E08es8w4LJpxBw@mail.gmail.com>
 <87fsiyuhyz.ffs@tglx> <CAHk-=wjEDJ4+xg0CWR7CaCKnO6Nhzn+vjJy7CjaVmf9R+g_3ag@mail.gmail.com>
 <CAHk-=wj6U3UamfLLV+rPu1WmKG_w3p0Bg=YbQcG1DxHpmP40Ag@mail.gmail.com>
 <CAHk-=wiYHXeWnF8Ea5xb735ehJ8FbjTT6UCvHYjX=Ooc7Z5sOw@mail.gmail.com> <0e038c2795784b7eb4de52f77b67206a@AcuMS.aculab.com>
In-Reply-To: <0e038c2795784b7eb4de52f77b67206a@AcuMS.aculab.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 19 Jul 2022 09:27:02 -0700
Message-ID: <CAHk-=whycTCSPwqV53ybUX=fDKMDk_Y8JaLug3KfUSiMF2TOQg@mail.gmail.com>
Subject: Re: [patch 00/38] x86/retbleed: Call depth tracking mitigation
To:     David Laight <David.Laight@aculab.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Sami Tolvanen <samitolvanen@google.com>,
        Joao Moreira <joao@overdrivepizza.com>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        "Cooper, Andrew" <andrew.cooper3@citrix.com>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Johannes Wikner <kwikner@ethz.ch>,
        Alyssa Milburn <alyssa.milburn@linux.intel.com>,
        Jann Horn <jannh@google.com>, "H.J. Lu" <hjl.tools@gmail.com>,
        "Moreira, Joao" <joao.moreira@intel.com>,
        "Nuzman, Joseph" <joseph.nuzman@intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        "Gross, Jurgen" <jgross@suse.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Peter Collingbourne <pcc@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Tue, Jul 19, 2022 at 1:26 AM David Laight <David.Laight@aculab.com> wrote:
>
> Shouldn't it be testing the value the caller supplied?

Actually, I'm just all confused.

All that verification code is *in* the caller, before the call - to
verify that the target looks fine.

I think I was confused by the hash thunk above the function also being
generated with a "cmpl $hash". And I don't even know why that is, and
why it wasn't just the bare constant.

            Linus