From: Masami Hiramatsu <email@example.com> To: Masami Hiramatsu <firstname.lastname@example.org> Cc: Andrew Cooper <email@example.com>, Ingo Molnar <firstname.lastname@example.org>, Juergen Gross <email@example.com>, "Stefano Stabellini" <firstname.lastname@example.org>, Peter Zijlstra <email@example.com>, Randy Dunlap <firstname.lastname@example.org>, <email@example.com>, <firstname.lastname@example.org>, Borislav Petkov <email@example.com>, "Josh Poimboeuf" <firstname.lastname@example.org>, <email@example.com>, "Boris Ostrovsky" <firstname.lastname@example.org> Subject: Re: [Xen-devel] [PATCH -tip 0/2] x86: Prohibit kprobes on XEN_EMULATE_PREFIX Date: Thu, 5 Sep 2019 22:09:58 +0900 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <firstname.lastname@example.org> On Thu, 5 Sep 2019 20:32:24 +0900 Masami Hiramatsu <email@example.com> wrote: > On Thu, 5 Sep 2019 08:54:17 +0100 > Andrew Cooper <firstname.lastname@example.org> wrote: > > > On 05/09/2019 02:49, Masami Hiramatsu wrote: > > > On Wed, 4 Sep 2019 12:54:55 +0100 > > > Andrew Cooper <email@example.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 Hmm, I think I might misunderstand what the "emulate prefix"... that is not a prefix which replace actual prefix, but just works like an escape sequence. Thus the next instruction can have any x86 prefix, correct? If so, this patch doesn't work. I have to add a new field in struct insn like "insn.emulate_prefix_size" so that we can keep a room for the prefixes for real instruction. Thank you, -- Masami Hiramatsu <firstname.lastname@example.org>
next prev parent reply other threads:[~2019-09-05 13:10 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 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 [this message] 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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