From: Jon Masters <jcm@redhat.com>
To: speck@linutronix.de
Subject: [MODERATED] Encrypted Message
Date: Fri, 1 Mar 2019 17:14:21 -0500 [thread overview]
Message-ID: <f19c8e25-c539-0857-4ec4-ffbf52bc085b@redhat.com> (raw)
In-Reply-To: <b28d3720-46af-6e37-eddd-ffab4465ef1a@redhat.com>
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From: Jon Masters <jcm@redhat.com>
To: speck for Jon Masters <speck@linutronix.de>
Subject: Re: [patch V4 04/11] x86/speculation/mds: Add mds_clear_cpu_buffer()
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On 3/1/19 3:58 PM, speck for Jon Masters wrote:
> On 2/26/19 9:19 AM, speck for Josh Poimboeuf wrote:
>
>> On Fri, Feb 22, 2019 at 11:24:22PM +0100, speck for Thomas Gleixner wrote:
>>> +MFBDS leaks Fill Buffer Entries. Fill buffers are used internally to manage
>>> +L1 miss situations and to hold data which is returned or sent in response
>>> +to a memory or I/O operation. Fill buffers can forward data to a load
>>> +operation and also write data to the cache. When the fill buffer is
>>> +deallocated it can retain the stale data of the preceding operations which
>>> +can then be forwarded to a faulting or assisting load operation, which can
>>> +be exploited under certain conditions. Fill buffers are shared between
>>> +Hyper-Threads so cross thread leakage is possible.
>
> The fill buffers sit opposite the L1D$ and participate in coherency
> directly. They supply data directly to the load store units. Here's the
> internal summary I wrote (feel free to use any of it that is useful):
>
> "Intel processors utilize fill buffers to perform loads of data when a
> miss occurs in the Level 1 data cache. The fill buffer allows the
> processor to implement a non-blocking cache, continuing with other
> operations while the necessary cache data “line” is loaded from a higher
> level cache or from memory. It also allows the result of the fill to be
> forwarded directly to the EU (Execution Unit) requiring the load,
> without waiting for it to be written into the L1 Data Cache.
>
> A load operation is not decoupled in the same way that a store is, but
> it does involve an AGU (Address Generation Unit) operation. If the AGU
> generates a fault (#PF, etc.) or an assist (A/D bits) then the classical
> Intel design would block the load and later reissue it. In contemporary
> designs, it instead allows subsequent speculation operations to
> temporarily see a forwarded data value from the fill buffer slot prior
> to the load actually taking place. Thus it is possible to read data that
> was recently accessed by another thread, if the fill buffer entry is not
> reused.
>
> It is this attack that allows cross-thread SMT leakage and breaks HT
> without recourse other than to disable it or to implement core
> scheduling in the Linux kernel.
>
> Variants of this include loads that cross cache or page boundaries due
> to further optimizations in Intel’s implementation. For example, Intel
> incorporate logic to guess at address generation prior to determining
> whether it crosses such a boundary (covered in US5335333A) and will
> forward this to the TLB/load logic prior to resolving the full address.
> They will retry the load by re-issuing uops in the case of a cross
> cacheline/page boundary but in that case will leak state as well."
Btw, I've various reproducers here that I'm happy to share if useful
with the right folks. Thomas and Linus should already have my IFU one
for later testing of that, I've also e.g. an FBBF. Currently it just
spews whatever it sees from the other threads, but in the next few days
I'll have it cleaned up to send/receive specific messages - then can
just wrap it with a bow so it can print yes/no vulnerable.
Ping if you have a need for a repro (keybase/email) and I'll go through
our process for sharing as appropriate.
Jon.
--
Computer Architect | Sent with my Fedora powered laptop
next prev parent reply other threads:[~2019-03-01 22:14 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-22 22:24 [patch V4 00/11] MDS basics Thomas Gleixner
2019-02-22 22:24 ` [patch V4 01/11] x86/msr-index: Cleanup bit defines Thomas Gleixner
2019-02-22 22:24 ` [patch V4 02/11] x86/speculation/mds: Add basic bug infrastructure for MDS Thomas Gleixner
2019-02-23 1:28 ` [MODERATED] " Linus Torvalds
2019-02-23 7:42 ` Thomas Gleixner
2019-02-27 13:04 ` Thomas Gleixner
2019-02-22 22:24 ` [patch V4 03/11] x86/kvm: Expose X86_FEATURE_MD_CLEAR to guests Thomas Gleixner
2019-02-22 22:24 ` [patch V4 04/11] x86/speculation/mds: Add mds_clear_cpu_buffer() Thomas Gleixner
2019-02-25 16:06 ` [MODERATED] " Frederic Weisbecker
2019-02-26 14:19 ` Josh Poimboeuf
2019-03-01 20:58 ` [MODERATED] Encrypted Message Jon Masters
2019-03-01 22:14 ` Jon Masters [this message]
2019-02-26 15:00 ` [MODERATED] Re: [patch V4 04/11] x86/speculation/mds: Add mds_clear_cpu_buffer() David Woodhouse
2019-02-22 22:24 ` [patch V4 05/11] x86/speculation/mds: Clear CPU buffers on exit to user Thomas Gleixner
2019-02-25 21:04 ` [MODERATED] " Greg KH
2019-02-26 15:20 ` Josh Poimboeuf
2019-02-26 20:26 ` Thomas Gleixner
2019-02-22 22:24 ` [patch V4 06/11] x86/speculation/mds: Conditionally clear CPU buffers on idle entry Thomas Gleixner
2019-02-25 21:09 ` [MODERATED] " Greg KH
2019-02-26 15:31 ` Josh Poimboeuf
2019-02-26 20:20 ` Thomas Gleixner
2019-02-22 22:24 ` [patch V4 07/11] x86/speculation/mds: Add mitigation control for MDS Thomas Gleixner
2019-02-25 20:17 ` [MODERATED] " mark gross
2019-02-26 15:50 ` Josh Poimboeuf
2019-02-26 20:16 ` Thomas Gleixner
2019-02-22 22:24 ` [patch V4 08/11] x86/speculation/mds: Add sysfs reporting " Thomas Gleixner
2019-02-22 22:24 ` [patch V4 09/11] x86/speculation/mds: Add mitigation mode VMWERV Thomas Gleixner
2019-02-23 9:52 ` [MODERATED] " Greg KH
2019-02-25 20:31 ` mark gross
2019-02-26 0:34 ` Andrew Cooper
2019-02-26 18:51 ` mark gross
2019-02-26 19:29 ` Thomas Gleixner
2019-02-22 22:24 ` [patch V4 10/11] Documentation: Move L1TF to separate directory Thomas Gleixner
2019-02-23 8:41 ` [MODERATED] " Greg KH
2019-02-22 22:24 ` [patch V4 11/11] Documentation: Add MDS vulnerability documentation Thomas Gleixner
2019-02-23 9:58 ` [MODERATED] " Greg KH
2019-02-26 20:11 ` Thomas Gleixner
2019-02-25 18:02 ` [MODERATED] " Dave Hansen
2019-02-26 20:10 ` Thomas Gleixner
2019-02-23 0:53 ` [MODERATED] Re: [patch V4 00/11] MDS basics Andrew Cooper
2019-02-23 14:12 ` Peter Zijlstra
2019-02-25 16:38 ` mark gross
2019-02-26 19:58 ` Thomas Gleixner
2019-02-26 16:28 ` [MODERATED] " Tyler Hicks
2019-02-26 19:58 ` Thomas Gleixner
2019-02-26 18:58 ` [MODERATED] " Kanth Ghatraju
2019-02-26 19:59 ` Thomas Gleixner
-- strict thread matches above, loose matches on Subject: below --
2019-03-05 16:43 [MODERATED] Starting to go public? Linus Torvalds
2019-03-05 17:02 ` [MODERATED] " Andrew Cooper
2019-03-05 20:36 ` Jiri Kosina
2019-03-05 22:31 ` Andrew Cooper
2019-03-06 16:18 ` [MODERATED] Encrypted Message Jon Masters
2019-03-05 17:10 ` Jon Masters
2019-03-04 1:21 [MODERATED] [PATCH RFC 0/4] Proposed cmdline improvements Josh Poimboeuf
2019-03-04 1:23 ` [MODERATED] [PATCH RFC 1/4] 1 Josh Poimboeuf
2019-03-04 3:55 ` [MODERATED] Encrypted Message Jon Masters
2019-03-04 7:30 ` [MODERATED] Re: [PATCH RFC 1/4] 1 Greg KH
2019-03-04 7:45 ` [MODERATED] Encrypted Message Jon Masters
2019-03-04 1:24 ` [MODERATED] [PATCH RFC 3/4] 3 Josh Poimboeuf
2019-03-04 3:58 ` [MODERATED] Encrypted Message Jon Masters
2019-03-04 17:17 ` [MODERATED] " Josh Poimboeuf
2019-03-06 16:22 ` [MODERATED] " Jon Masters
2019-03-04 1:25 ` [MODERATED] [PATCH RFC 4/4] 4 Josh Poimboeuf
2019-03-04 4:07 ` [MODERATED] Encrypted Message Jon Masters
2019-03-01 21:47 [patch V6 00/14] MDS basics 0 Thomas Gleixner
2019-03-01 21:47 ` [patch V6 06/14] MDS basics 6 Thomas Gleixner
2019-03-04 6:28 ` [MODERATED] Encrypted Message Jon Masters
2019-03-01 21:47 ` [patch V6 08/14] MDS basics 8 Thomas Gleixner
2019-03-04 6:57 ` [MODERATED] Encrypted Message Jon Masters
2019-03-04 7:06 ` Jon Masters
2019-03-04 8:12 ` Jon Masters
2019-03-05 15:34 ` Thomas Gleixner
2019-03-06 16:21 ` [MODERATED] " Jon Masters
2019-03-01 21:47 ` [patch V6 10/14] MDS basics 10 Thomas Gleixner
2019-03-04 6:45 ` [MODERATED] Encrypted Message Jon Masters
2019-03-01 21:47 ` [patch V6 12/14] MDS basics 12 Thomas Gleixner
2019-03-04 5:47 ` [MODERATED] Encrypted Message Jon Masters
2019-03-04 5:30 ` Jon Masters
2019-02-24 15:07 [MODERATED] [PATCH v6 00/43] MDSv6 Andi Kleen
2019-02-24 15:07 ` [MODERATED] [PATCH v6 10/43] MDSv6 Andi Kleen
2019-02-25 16:30 ` [MODERATED] " Greg KH
2019-02-25 16:41 ` [MODERATED] Encrypted Message Jon Masters
2019-02-24 15:07 ` [MODERATED] [PATCH v6 31/43] MDSv6 Andi Kleen
2019-02-25 15:19 ` [MODERATED] " Greg KH
2019-02-25 15:34 ` Andi Kleen
2019-02-25 15:49 ` Greg KH
2019-02-25 15:52 ` [MODERATED] Encrypted Message Jon Masters
2019-02-25 16:00 ` [MODERATED] " Greg KH
2019-02-25 16:19 ` [MODERATED] " Jon Masters
2019-02-21 23:44 [patch V3 0/9] MDS basics 0 Thomas Gleixner
2019-02-21 23:44 ` [patch V3 4/9] MDS basics 4 Thomas Gleixner
2019-02-22 7:45 ` [MODERATED] Encrypted Message Jon Masters
2019-02-20 15:07 [patch V2 00/10] MDS basics+ 0 Thomas Gleixner
2019-02-20 15:07 ` [patch V2 04/10] MDS basics+ 4 Thomas Gleixner
2019-02-20 17:10 ` [MODERATED] " mark gross
2019-02-21 19:26 ` [MODERATED] Encrypted Message Tim Chen
2019-02-19 12:44 [patch 0/8] MDS basics 0 Thomas Gleixner
2019-02-21 16:14 ` [MODERATED] Encrypted Message Jon Masters
2019-02-07 23:41 [MODERATED] [PATCH v3 0/6] PERFv3 Andi Kleen
2019-02-07 23:41 ` [MODERATED] [PATCH v3 2/6] PERFv3 Andi Kleen
2019-02-08 0:51 ` [MODERATED] Re: [SUSPECTED SPAM][PATCH " Andrew Cooper
2019-02-08 9:01 ` Peter Zijlstra
2019-02-08 9:39 ` Peter Zijlstra
2019-02-08 10:53 ` [MODERATED] [RFC][PATCH] performance walnuts Peter Zijlstra
2019-02-15 23:45 ` [MODERATED] Encrypted Message Jon Masters
2019-01-12 1:29 [MODERATED] [PATCH v4 00/28] MDSv4 2 Andi Kleen
2019-01-12 1:29 ` [MODERATED] [PATCH v4 05/28] MDSv4 10 Andi Kleen
2019-01-14 19:20 ` [MODERATED] " Dave Hansen
2019-01-18 7:33 ` [MODERATED] Encrypted Message Jon Masters
2019-01-14 23:39 ` Tim Chen
2019-01-12 1:29 ` [MODERATED] [PATCH v4 10/28] MDSv4 24 Andi Kleen
2019-01-15 1:05 ` [MODERATED] Encrypted Message Tim Chen
2018-06-12 17:29 [MODERATED] FYI - Reading uncached memory Jon Masters
2018-06-14 16:59 ` [MODERATED] Encrypted Message Tim Chen
2018-05-29 19:42 [MODERATED] [PATCH 0/2] L1TF KVM 0 Paolo Bonzini
[not found] ` <20180529194240.7F1336110A@crypto-ml.lab.linutronix.de>
2018-05-29 22:49 ` [PATCH 1/2] L1TF KVM 1 Thomas Gleixner
2018-05-29 23:54 ` [MODERATED] " Andrew Cooper
2018-05-30 9:01 ` Paolo Bonzini
2018-06-04 8:24 ` [MODERATED] " Martin Pohlack
2018-06-04 13:11 ` [MODERATED] Is: Tim, Q to you. Was:Re: " Konrad Rzeszutek Wilk
2018-06-04 17:59 ` [MODERATED] Encrypted Message Tim Chen
2018-06-05 23:34 ` Tim Chen
2018-06-05 23:37 ` Tim Chen
2018-06-07 19:11 ` Tim Chen
2018-05-17 20:53 SSB status - V18 pushed out Thomas Gleixner
2018-05-18 13:54 ` [MODERATED] Is: Sleep states ?Was:Re: " Konrad Rzeszutek Wilk
2018-05-18 14:29 ` Thomas Gleixner
2018-05-18 19:50 ` [MODERATED] Encrypted Message Tim Chen
2018-05-02 21:51 [patch V11 00/16] SSB 0 Thomas Gleixner
2018-05-03 4:27 ` [MODERATED] Encrypted Message Tim Chen
2018-04-24 9:06 [MODERATED] L1D-Fault KVM mitigation Joerg Roedel
2018-04-24 9:35 ` [MODERATED] " Peter Zijlstra
2018-04-24 9:48 ` David Woodhouse
2018-04-24 11:04 ` Peter Zijlstra
2018-05-23 9:45 ` David Woodhouse
2018-05-24 9:45 ` Peter Zijlstra
2018-05-24 15:04 ` Thomas Gleixner
2018-05-24 15:33 ` Thomas Gleixner
2018-05-24 23:18 ` [MODERATED] Encrypted Message Tim Chen
2018-05-25 18:22 ` Tim Chen
2018-05-26 19:14 ` L1D-Fault KVM mitigation Thomas Gleixner
2018-05-29 19:29 ` [MODERATED] Encrypted Message Tim Chen
2018-05-29 21:14 ` L1D-Fault KVM mitigation Thomas Gleixner
2018-05-30 16:38 ` [MODERATED] Encrypted Message Tim Chen
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