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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>, Juergen Gross <jgross@suse.com>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Randy Dunlap <rdunlap@infradead.org>, <x86@kernel.org>,
	<linux-kernel@vger.kernel.org>, Borislav Petkov <bp@alien8.de>,
	"Josh Poimboeuf" <jpoimboe@redhat.com>,
	<xen-devel@lists.xenproject.org>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>
Subject: Re: [Xen-devel] [PATCH -tip 0/2] x86: Prohibit kprobes on XEN_EMULATE_PREFIX
Date: Thu, 5 Sep 2019 08:54:17 +0100	[thread overview]
Message-ID: <1372ce73-e2d8-6144-57df-a98429587826@citrix.com> (raw)
In-Reply-To: <20190905104937.60aa03f699a9c0fbf1b651b9@kernel.org>

On 05/09/2019 02:49, Masami Hiramatsu wrote:
> On Wed, 4 Sep 2019 12:54:55 +0100
> Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>
>> On 04/09/2019 12:45, Masami Hiramatsu wrote:
>>> Hi,
>>>
>>> These patches allow x86 instruction decoder to decode
>>> xen-cpuid which has XEN_EMULATE_PREFIX, and prohibit
>>> kprobes to probe on it.
>>>
>>> Josh reported that the objtool can not decode such special
>>> prefixed instructions, and I found that we also have to
>>> prohibit kprobes to probe on such instruction.
>>>
>>> This series can be applied on -tip master branch which
>>> has merged Josh's objtool/perf sharing common x86 insn
>>> decoder series.
>> The paravirtualised xen-cpuid is were you'll see it most in a regular
>> kernel, but be aware that it is also used for testing purposes in other
>> circumstances, and there is an equivalent KVM prefix which is used for
>> KVM testing.
> Good catch! I didn't notice that. Is that really same sequance or KVM uses
> another sequence of instructions for KVM prefix?

I don't know if you've spotted, but the prefix is a ud2a instruction
followed by 'xen' in ascii.

The KVM version was added in c/s 6c86eedc206dd1f9d37a2796faa8e6f2278215d2

>
>> It might be better to generalise the decode support to "virtualisation
>> escape prefix" or something slightly more generic.
> Agreed, it is easy to expand it, we can switch the prefix template.
> Could you tell me where I should look? I will add it.

These are the only two I'm aware of.

~Andrew

  reply	other threads:[~2019-09-05  7:54 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-04 11:45 Masami Hiramatsu
2019-09-04 11:45 ` [PATCH -tip 1/2] x86: xen: insn: Decode XEN_EMULATE_PREFIX correctly Masami Hiramatsu
2019-09-04 11:46 ` [PATCH -tip 2/2] x86: kprobes: Prohibit probing on instruction which has Xen prefix Masami Hiramatsu
2019-09-04 11:54 ` [Xen-devel] [PATCH -tip 0/2] x86: Prohibit kprobes on XEN_EMULATE_PREFIX Andrew Cooper
2019-09-05  1:49   ` Masami Hiramatsu
2019-09-05  7:54     ` Andrew Cooper [this message]
2019-09-05  8:26       ` Peter Zijlstra
2019-09-05  8:53         ` Andrew Cooper
2019-09-05  9:26           ` Peter Zijlstra
2019-09-05  9:38             ` Andrew Cooper
2019-09-05 12:49           ` [OT] " Masami Hiramatsu
2019-09-05 11:32       ` Masami Hiramatsu
2019-09-05 13:09         ` Masami Hiramatsu
2019-09-05 13:31           ` Andrew Cooper
2019-09-05 16:12             ` Masami Hiramatsu
2019-09-04 12:02 ` Peter Zijlstra

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