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

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Message-ID: <Ytg6UD+0F6zv981o@worktop.programming.kicks-ass.net>
Date:   Wed, 20 Jul 2022 19:24:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        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>,
        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>,
        Juergen Gross <jgross@...e.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [patch 00/38] x86/retbleed: Call depth tracking mitigation

On Wed, Jul 20, 2022 at 10:09:37AM -0700, Linus Torvalds wrote:
> On Wed, Jul 20, 2022 at 9:57 AM Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > [    2.488712] WARNING: CPU: 0 PID: 0 at arch/x86/kernel/alternative.c:558 apply_returns+0xa3/0x1ec
> 
> That warning is kind of annoying, in how it doesn't actually give any
> information about where the problem is.
> 
> I do note that we only fix up JMP32_INSN_OPCODE, and I wonder if we
> have a "jmp __x86_return_thunk" that is close enough to the return
> thunk that it actually uses a byte offset?
> 
> But that WARN_ON_ONCE() should probably be changed to actually give
> some information about where the problem is.

There's a patch for that:

  https://lkml.kernel.org/r/20220713213819.460771-1-keescook@chromium.org

it seems to have gotten lost, let me go queue that.