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From: Peter Zijlstra <peterz@infradead.org>
To: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Linux-Kernel <linux-kernel@vger.kernel.org>,
	mingo@redhat.com, konrad.wilk@oracle.com, dwmw@amazon.co.uk,
	tglx@linutronix.de,
	Srinivas REDDY Eeda <srinivas.eeda@oracle.com>,
	bp@suse.de, hpa@zytor.com
Subject: Re: [PATCH 3/3] kprobes/x86: Simplify indirect-jump check in retpoline
Date: Thu, 1 Nov 2018 09:56:34 +0100	[thread overview]
Message-ID: <20181101085634.GC3159@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <04040fa2-02c6-9aa6-15fe-609ad21b3426@oracle.com>

On Thu, Nov 01, 2018 at 10:02:14AM +0800, Zhenzhong Duan wrote:
> > Hmm, what about the case where we have RETPOLINE runtime disabled? Then
> > the CALL_NOSPEC alternative patches in an indirect call again, and the
> > retpolines are gone.
> 
> Is RETPOLINE runtime toggle supported in upstream? I don't see such code.

arch/x86/kernel/cpu/bugs.c look for the "nospectre_v2" and related
options. That will avoid X86_FEATURE_RETPOLINE from being set, and thus
the JMP_NOSPEC and CALL_NOSPEC alternatives will not patch out the
indirect jump / call.

  reply	other threads:[~2018-11-01  8:56 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-30  6:55 [PATCH 3/3] kprobes/x86: Simplify indirect-jump check in retpoline Zhenzhong Duan
2018-10-30  8:36 ` Peter Zijlstra
2018-10-31  6:01   ` Zhenzhong Duan
2018-10-31 13:53     ` Peter Zijlstra
2018-10-31 14:00       ` Peter Zijlstra
2018-11-01  2:02         ` Zhenzhong Duan
2018-11-01  8:56           ` Peter Zijlstra [this message]
2018-11-01  9:21             ` Zhenzhong Duan

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