From: Juergen Gross <jgross@suse.com>
To: Jiri Kosina <jikos@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@suse.de>,
Mike Latimer <mlatimer@suse.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/pti: don't report XenPV as vulnerable
Date: Fri, 15 Jun 2018 08:30:22 +0200 [thread overview]
Message-ID: <821642fe-775b-e68c-2a66-73b73c810289@suse.com> (raw)
In-Reply-To: <nycvar.YFH.7.76.1806150815440.6203@cbobk.fhfr.pm>
On 15/06/18 08:16, Jiri Kosina wrote:
> On Fri, 15 Jun 2018, Juergen Gross wrote:
>
>>>> wrong for 64-bit, too, in case the mitigation is disabled at hypervisor
>>>> level.
>>>
>>> If that is indeed possible (is it?), then the check we have in
>>> pti_check_boottime_disable() is wrong as well.
>>
>> No, it isn't. PTI for 32-bit kernels isn't paravirtualized, so it has to
>> be disabled.
>
> I was talking about this "mitigation disabled at Xen hypervisor level for
> 64-bit" situation though.
>
Why? PTI has to be disabled in PV guests as it can't work there due to
missing paravirtualization of the PTI feature (mov to/from %cr3).
The Xen meltdown mitigation ("XPTI") for 64-bit pv guests is primarily
securing the hypervisor against meltdown attacks of the guest. The guest
itself can't do anything in this regard in 64-bit mode, as user and
kernel code are already using different %cr3 values even without PTI.
Juergen
next prev parent reply other threads:[~2018-06-15 6:30 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-14 22:32 Jiri Kosina
2018-06-15 5:46 ` Juergen Gross
2018-06-15 6:04 ` Jiri Kosina
2018-06-15 6:10 ` Juergen Gross
2018-06-15 6:16 ` Jiri Kosina
2018-06-15 6:30 ` Juergen Gross [this message]
2018-06-15 6:39 ` Jiri Kosina
2018-06-15 7:00 ` Juergen Gross
2018-06-15 21:10 ` Jiri Kosina
2018-06-16 6:36 ` Juergen Gross
2018-06-18 7:59 ` [PATCH v2] " Jiri Kosina
2018-06-18 8:07 ` Juergen Gross
2018-06-19 8:02 ` [tip:x86/pti] x86/pti: Don't " tip-bot for Jiri Kosina
2018-06-21 12:24 ` tip-bot for Jiri Kosina
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