From: Zhenzhong Duan <zhenzhong.duan@oracle.com>
To: Peter Zijlstra <peterz@infradead.org>
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 17:21:38 +0800 [thread overview]
Message-ID: <e5de6bcd-a7d1-7d48-868f-1a5168332dfc@oracle.com> (raw)
In-Reply-To: <20181101085634.GC3159@hirez.programming.kicks-ass.net>
On 2018/11/1 16:56, Peter Zijlstra wrote:
> 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.
>
Yes, in this case there are also indirect branches. I'll drop 3rd patch
in v2.
Thanks
Zhenzhong
prev parent reply other threads:[~2018-11-01 9:21 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
2018-11-01 9:21 ` Zhenzhong Duan [this message]
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