From: Paolo Bonzini <pbonzini@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Xiaoyao Li <xiaoyao.li@intel.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Andy Lutomirski <luto@amacapital.net>
Cc: x86@kernel.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org,
David Laight <David.Laight@aculab.com>
Subject: Re: [PATCH v2 3/6] kvm: x86: Emulate split-lock access as a write
Date: Tue, 11 Feb 2020 14:34:18 +0100 [thread overview]
Message-ID: <d690c2e3-e9ef-a504-ede3-d0059ec1e0f6@redhat.com> (raw)
In-Reply-To: <878sl945tj.fsf@nanos.tec.linutronix.de>
On 11/02/20 14:22, Thomas Gleixner wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
>> On 03/02/20 16:16, Xiaoyao Li wrote:
>>> A sane guest should never tigger emulation on a split-lock access, but
>>> it cannot prevent malicous guest from doing this. So just emulating the
>>> access as a write if it's a split-lock access to avoid malicous guest
>>> polluting the kernel log.
>>
>> Saying that anything doing a split lock access is malicious makes little
>> sense.
>
> Correct, but we also have to accept, that split lock access can be used
> in a malicious way, aka. DoS.
Indeed, a more accurate emulation such as temporarily disabling
split-lock detection in the emulator would allow the guest to use split
lock access as a vehicle for DoS, but that's not what the commit message
says. If it were only about polluting the kernel log, there's
printk_ratelimited for that. (In fact, if we went for incorrect
emulation as in this patch, a rate-limited pr_warn would be a good idea).
It is much more convincing to say that since this is pretty much a
theoretical case, we can assume that it is only done with the purpose of
DoS-ing the host or something like that, and therefore we kill the guest.
>> Split lock detection is essentially a debugging feature, there's a
>> reason why the MSR is called "TEST_CTL". So you don't want to make the
>
> The fact that it ended up in MSR_TEST_CTL does not say anything. That's
> where they it ended up to be as it was hastily cobbled together for
> whatever reason.
Or perhaps it was there all the time in test silicon or something like
that... That would be a very plausible reason for all the quirks behind it.
Paolo
next prev parent reply other threads:[~2020-02-11 13:34 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-03 15:16 [PATCH v2 0/6] kvm/split_lock: Add feature split lock detection support in kvm Xiaoyao Li
2020-02-03 15:16 ` [PATCH v2 1/6] x86/split_lock: Add and export get_split_lock_detect_state() Xiaoyao Li
2020-02-03 21:45 ` Sean Christopherson
2020-02-03 15:16 ` [PATCH v2 2/6] x86/split_lock: Add and export split_lock_detect_set() Xiaoyao Li
2020-02-03 15:16 ` [PATCH v2 3/6] kvm: x86: Emulate split-lock access as a write Xiaoyao Li
2020-02-03 20:54 ` Sean Christopherson
2020-02-04 2:55 ` Xiaoyao Li
2020-02-11 12:20 ` Paolo Bonzini
2020-02-11 13:22 ` Thomas Gleixner
2020-02-11 13:34 ` Paolo Bonzini [this message]
2020-02-11 14:02 ` Xiaoyao Li
2020-02-11 14:34 ` David Laight
2020-02-27 0:11 ` Sean Christopherson
2020-03-12 11:42 ` Xiaoyao Li
2020-03-12 15:00 ` Paolo Bonzini
2020-02-03 15:16 ` [PATCH v2 4/6] kvm: vmx: Extend VMX's #AC handding for split lock in guest Xiaoyao Li
2020-02-03 21:14 ` Sean Christopherson
2020-02-04 6:46 ` Xiaoyao Li
2020-02-10 21:30 ` Sean Christopherson
2020-02-03 15:16 ` [PATCH v2 5/6] kvm: x86: Emulate MSR IA32_CORE_CAPABILITIES Xiaoyao Li
2020-02-03 21:43 ` Sean Christopherson
2020-02-04 9:19 ` Xiaoyao Li
2020-02-04 9:37 ` Peter Zijlstra
2020-02-11 3:52 ` Andy Lutomirski
2020-02-11 12:38 ` Peter Zijlstra
2020-02-03 15:16 ` [PATCH v2 6/6] x86: vmx: virtualize split lock detection Xiaoyao Li
2020-02-03 15:58 ` Xiaoyao Li
2020-02-03 18:52 ` Andy Lutomirski
2020-02-03 21:42 ` Sean Christopherson
2020-02-04 2:52 ` Xiaoyao Li
2020-02-04 5:35 ` Sean Christopherson
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