From: "Tian, Kevin" <kevin.tian@intel.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
Xen-devel <xen-devel@lists.xen.org>
Cc: "Tamas K Lengyel" <tamas@tklengyel.com>,
"Wei Liu" <wei.liu2@citrix.com>,
"Jan Beulich" <JBeulich@suse.com>,
"Razvan Cojocaru" <rcojocaru@bitdefender.com>,
"Nakajima, Jun" <jun.nakajima@intel.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH v2 3/4] x86/vmx: Fix security issue when a guest balloons out the #VE info page
Date: Thu, 28 Feb 2019 05:48:12 +0000 [thread overview]
Message-ID: <AADFC41AFE54684AB9EE6CBC0274A5D19C96B354@SHSMSX104.ccr.corp.intel.com> (raw)
In-Reply-To: <1550780337-638-1-git-send-email-andrew.cooper3@citrix.com>
> From: Andrew Cooper [mailto:andrew.cooper3@citrix.com]
> Sent: Friday, February 22, 2019 4:19 AM
>
> The logic in altp2m_vcpu_{en,dis}able_ve() and
> vmx_vcpu_update_vmfunc_ve() is
> dangerous. After #VE has been set up, the guest can balloon out and free the
> nominated GFN, after which the processor may write to it. Also, the unlocked
> GFN query means the MFN is stale by the time it is used. Alternatively, a
> guest can race two disable calls to cause one VMCS to still reference the
> nominated GFN after the tracking information was dropped.
>
> Rework the logic from scratch to make it safe.
>
> Hold an extra page reference on the underlying frame, to account for the
> VMCS's reference. This means that if the GFN gets ballooned out, it isn't
> freed back to Xen until #VE is disabled, and the VMCS no longer refers to the
> page.
>
> A consequence of this is that altp2m_vcpu_disable_ve() needs to be called
> during the domain_kill() path, to drop the reference for domains which shut
> down with #VE still enabled.
>
> For domains using altp2m, we expect a single enable call and no disable for
> the remaining lifetime of the domain. However, to avoid problems with
> concurrent calls, use cmpxchg() to locklessly maintain safety.
>
> This doesn't have an XSA because altp2m is not yet a security-supported
> feature.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Release-acked-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
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next prev parent reply other threads:[~2019-02-28 5:48 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-19 22:18 [PATCH tentitively for-4.12 0/4] x86/altp2m: Fix multiple security issues Andrew Cooper
2019-02-19 22:18 ` [PATCH 1/4] xen/common: Break domain_unmap_resources() out of domain_kill() Andrew Cooper
2019-02-19 22:39 ` Razvan Cojocaru
2019-02-19 22:46 ` Andrew Cooper
2019-02-20 14:11 ` Jan Beulich
2019-02-19 22:18 ` [PATCH 2/4] x86/altp2m: Rework #VE enable/disable paths Andrew Cooper
2019-02-19 23:10 ` Razvan Cojocaru
2019-02-20 14:14 ` Jan Beulich
2019-02-19 22:18 ` [PATCH 3/4] x86/vmx: Fix security issue when a guest balloons out the #VE info page Andrew Cooper
2019-02-20 9:45 ` Razvan Cojocaru
2019-02-20 14:37 ` Jan Beulich
2019-02-21 17:03 ` Andrew Cooper
2019-02-22 8:49 ` Jan Beulich
2019-02-21 20:18 ` [PATCH v2 " Andrew Cooper
2019-02-21 21:28 ` Razvan Cojocaru
2019-02-22 12:24 ` Jan Beulich
2019-02-22 14:03 ` Andrew Cooper
2019-02-28 5:48 ` Tian, Kevin [this message]
2019-02-19 22:18 ` [PATCH 4/4] x86/vmx: Properly flush the TLB when an altp2m is modified Andrew Cooper
2019-02-19 23:20 ` Razvan Cojocaru
2019-02-20 14:47 ` Jan Beulich
2019-02-28 5:50 ` Tian, Kevin
2019-02-21 13:13 ` [PATCH tentitively for-4.12 0/4] x86/altp2m: Fix multiple security issues Juergen Gross
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