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Xen官网安全更新(2021-06-08)

来源:Xen官网 发布日期:2021-06-08 阅读次数:4113 评论:0

基本信息

发布日期:2021-06-08(官方当地时间)

更新类型:安全更新

更新版本:未知

感知时间:2021-06-09 01:05:40

风险等级:未知

情报贡献:TSRC

更新标题

Speculative Code Store Bypass

更新详情




XSA-375 - Xen Security Advisories



InformationAdvisory XSA-375Public release 2021-06-08 17:00Updated 2021-06-08 17:04Version 2CVE(s) CVE-2021-0089Title Speculative Code Store BypassFilesadvisory-375.txt (signed advisory file)xsa375.metaxsa375.patchxsa375-4.12.patchxsa375-4.13.patchAdvisory-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

Xen Security Advisory CVE-2021-0089 / XSA-375
version 2

Speculative Code Store Bypass

UPDATES IN VERSION 2
====================

New 4.12 backport (also targeting 4.11), addressing a build issue.

Discuss the need for SPECULATIVE_HARDEN_BRANCH in Resolution.

Provide Arm information links.

Public release.

ISSUE DESCRIPTION
=================

Modern superscalar processors may employ sophisticated decoding and
caching of the instruction stream to improve performance. However, a
consequence is that self-modifying code updates may not take effect
instantly.

Whatever the architectural guarantees, some CPUs have microarchitectural
behaviour whereby the stale instruction stream may be speculatively
decoded and executed.

Speculation of this form can suffer from type confusion in registers,
and potentially leak data.

For more details, see:
https://www.vusec.net/projects/fpvi-scsb
https://www.amd.com/en/corporate-product-security-bulletin-amd-sb-1003
https://software.intel.com/content/www/us/en/develop/articles/software-security-guidance/advisory-guidance/speculative-code-store-bypass.html
https://software.intel.com/content/www/us/en/develop/articles/software-security-guidance/advisory-guidance/floating-point-value-injection.html
https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/frequently-asked-questions#scsb
https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/frequently-asked-questions#fvpi

IMPACT
======

In attacker might be able to infer the contents of arbitrary host
memory, including memory assigned to other guests.

VULNERABLE SYSTEMS
==================

Systems running all versions of Xen are affected.

Whether a CPU is potentially vulnerable depends on its
microarchitecture. Consult your hardware vendor.

Xen running on ARM does not have runtime self-modying code, so is
believed to be not vulnerable, irrespective of any hardware
susceptibility.

Xen running on x86 does have runtime self-modying code as part of
emulation, and is believed to be potentially vulnerable.

Xen is not vulnerable if retpoline or lfence mitigations for Spectre v2
protection are active. Protections depend on compiler support (as
indicated by INDIRECT_THUNK), and a runtime setting (BTI-Thunk):

# xl dmesg | grep -e INDIRECT_THUNK -e BTI-Thunk
(XEN) Compiled-in support: INDIRECT_THUNK SHADOW_PAGING
(XEN) Xen settings: BTI-Thunk RETPOLINE, SPEC_CTRL: IBRS+ SSBD-, Other: SRB_LOCK+ IBPB L1D_FLUSH VERW BRANCH_HARDEN

BTI-Thunk as either RETPOLINE or LFENCE prevents the vulnerability.

MITIGATION
==========

If Spectre v2 support is compiled in, but JMP is used by default,
RETPOLINE or LFENCE can be selected with `spec-ctrl=bti-thunk=retpoline`
or `spec-ctrl=bti-thunk=lfence`.

CREDITS
=======

This issue was discovered by Enrico Barberis, Hany Ragab, Herbert Bos,
and Cristiano Giuffrida from the VUSec group at VU Amsterdam.

RESOLUTION
==========

Applying the appropriate attached patch resolves this issue. Note that
in 4.13 and newer the patch will only take effect when the
SPECULATIVE_HARDEN_BRANCH hypervisor config option is enabled. 4.12 and
older do not have such an option, and the change will take effect
unconditionally.

Note that patches for released versions are generally prepared to
apply to the stable branches, and may not apply cleanly to the most
recent release tarball. Downstreams are encouraged to update to the
tip of the stable branch before applying these patches.

xsa375.patch xen-unstable - 4.14.x
xsa375-4.13.patch Xen 4.13.x
xsa375-4.12.patch Xen 4.12.x - 4.11.x

$ sha256sum xsa375*
367d5bb97c942b9f744a57645df87148772c0879de6f351f36f88147f3958e83 xsa375.meta
301ef80da837bc2af36a0958f35f42f4d267b20ec6e91ae5faf2616167ef49f8 xsa375.patch
dc024daf17242b6477a16a349754a94b2b25cbbfd8c14475741b778710a44c93 xsa375-4.12.patch
f70511d843c6617b932da11ffe857e2e3aa3834ccff07d4d0beba90d63a3dae2 xsa375-4.13.patch
$

NOTE CONCERNING CVE-2021-0086
=============================

Floating Point Value Injection (FPVI) was discovered and disclosed in
the same research as SCSB. Xen on x86 does in some cases emulate
floating point operations with guest provided inputs, but does not have
subsequent control flow dependent on results, transient or otherwise, of
the operation.

Therefore, we believe Xen is not vulnerable to FPVI, irrespective of any
hardware susceptibility.

DEPLOYMENT DURING EMBARGO
=========================

Deployment of the patches and/or mitigations described above (or
others which are substantially similar) is permitted during the
embargo, even on public-facing systems with untrusted guest users and
administrators.

But: Distribution of updated software is prohibited (except to other
members of the predisclosure list).

Predisclosure list members who wish to deploy significantly different
patches and/or mitigations, please contact the Xen Project Security
Team.


(Note: this during-embargo deployment notice is retained in
post-embargo publicly released Xen Project advisories, even though it
is then no longer applicable. This is to enable the community to have
oversight of the Xen Project Security Team's decisionmaking.)

For more information about permissible uses of embargoed information,
consult the Xen Project community's agreed Security Policy:
http://www.xenproject.org/security-policy.html
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Xenproject.org Security Team

软件描述

Xen 是一个开放源代码虚拟机监视器,由剑桥大学开发。它打算在单个计算机上运行多达100个满特征的操作系统。操作系统必须进行显式地修改(“移植”)以在Xen上运行(但是提供对用户应用的兼容性)。这使得Xen无需特殊硬件支持,就能达到高性能的虚拟化。

TSRC分析

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业界资讯

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