b014cb462c
changes since Xen 4.6.5: mostly bug fixes, including security fixes for XSA206, XSA211 to XSA244. PKGREVISION set to 1 to account for the fact that it's not a stock Xen 4.6.6. Note that, unlike upstream, pv-linear-pt defaults to true, so that NetBSD PV guests (including dom0) will continue to boot without changes to boot.cfg
56 lines
2.2 KiB
Text
56 lines
2.2 KiB
Text
$NetBSD: patch-XSA240,v 1.1 2017/10/17 10:57:34 bouyer Exp $
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From eeea00c427376c269ffa34587f16fa1182d8c29d Mon Sep 17 00:00:00 2001
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From: George Dunlap <george.dunlap@citrix.com>
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Date: Fri, 22 Sep 2017 11:46:55 +0100
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Subject: [PATCH 2/2] x86/mm: Disable PV linear pagetables by default
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Allowing pagetables to point to other pagetables of the same level
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(often called 'linear pagetables') has been included in Xen since its
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inception. But it is not used by the most common PV guests (Linux,
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NetBSD, minios), and has been the source of a number of subtle
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reference-counting bugs.
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Add a command-line option to control whether PV linear pagetables are
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allowed (disabled by default).
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Reported-by: Jann Horn <jannh@google.com>
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Signed-off-by: George Dunlap <george.dunlap@citrix.com>
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Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
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---
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Changes since v2:
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- s/_/-/; in command-line option
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- Added __read_mostly
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---
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docs/misc/xen-command-line.markdown | 15 +++++++++++++++
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xen/arch/x86/mm.c | 9 +++++++++
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2 files changed, 24 insertions(+)
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diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
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index d99a20a44b..c91acaa464 100644
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--- ../docs/misc/xen-command-line.markdown.orig
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+++ ../docs/misc/xen-command-line.markdown
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@@ -1231,6 +1231,21 @@ The following resources are available:
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the cache allocation.
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* `cat` instructs Xen to enable/disable Cache Allocation Technology.
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* `cos_max` indicates the max value for COS ID.
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+
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+### pv-linear-pt
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+> `= <boolean>`
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+
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+> Default: `true`
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+
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+Allow PV guests to have pagetable entries pointing to other pagetables
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+of the same level (i.e., allowing L2 PTEs to point to other L2 pages).
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+This technique is often called "linear pagetables", and is sometimes
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+used to allow operating systems a simple way to consistently map the
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+current process's pagetables into its own virtual address space.
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+
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+None of the most common PV operating systems (Linux, MiniOS)
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+use this technique, but NetBSD in PV mode, and maybe custom operating
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+systems do.
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### reboot
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> `= t[riple] | k[bd] | a[cpi] | p[ci] | P[ower] | e[fi] | n[o] [, [w]arm | [c]old]`
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diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
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index 81074aa473..75dd077046 100644
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