linux-kernel - Re: [tip: x86/bugs] x86/retpoline: Ensure default return thunk isn't used at runtime

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Message-ID: <20231018155433.z4auwckr5s27wnig@treble>
Date:   Wed, 18 Oct 2023 08:54:33 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        linux-tip-commits@...r.kernel.org,
        David Kaplan <david.kaplan@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org
Subject: Re: [tip: x86/bugs] x86/retpoline: Ensure default return thunk isn't
 used at runtime

On Wed, Oct 18, 2023 at 05:12:45PM +0200, Borislav Petkov wrote:
> On Wed, Oct 18, 2023 at 03:38:56PM +0200, Ingo Molnar wrote:
> > If then WARN_ONCE().
> 
> WARN_ONCE() is not enough considering that if this fires, it means we're
> not really properly protected against one of those RET-speculation
> things.
> 
> It needs to be warning constantly but then still allow booting. I.e,
> a ratelimited warn of sorts but I don't think we have that... yet.

I'm not sure a rate-limited WARN() would be a good thing.  Either the
user is regularly checking dmesg (most likely in some automated fashion)
or they're not.  If the latter, a rate-limited WARN() would wrap dmesg
pretty quickly.

-- 
Josh