diff options
Diffstat (limited to 'system/xen/xsa/xsa240-4.9-0002-x86-mm-Disable-PV-linear-pagetables-by-default.patch')
| -rw-r--r-- | system/xen/xsa/xsa240-4.9-0002-x86-mm-Disable-PV-linear-pagetables-by-default.patch | 83 |
1 files changed, 0 insertions, 83 deletions
diff --git a/system/xen/xsa/xsa240-4.9-0002-x86-mm-Disable-PV-linear-pagetables-by-default.patch b/system/xen/xsa/xsa240-4.9-0002-x86-mm-Disable-PV-linear-pagetables-by-default.patch deleted file mode 100644 index 5e057c5652..0000000000 --- a/system/xen/xsa/xsa240-4.9-0002-x86-mm-Disable-PV-linear-pagetables-by-default.patch +++ /dev/null @@ -1,83 +0,0 @@ -From e614979ce054044d9e19023f1ef10dae6e38baf4 Mon Sep 17 00:00:00 2001 -From: George Dunlap <george.dunlap@citrix.com> -Date: Fri, 22 Sep 2017 11:46:55 +0100 -Subject: [PATCH 2/2] x86/mm: Disable PV linear pagetables by default - -Allowing pagetables to point to other pagetables of the same level -(often called 'linear pagetables') has been included in Xen since its -inception. But it is not used by the most common PV guests (Linux, -NetBSD, minios), and has been the source of a number of subtle -reference-counting bugs. - -Add a command-line option to control whether PV linear pagetables are -allowed (disabled by default). - -Reported-by: Jann Horn <jannh@google.com> -Signed-off-by: George Dunlap <george.dunlap@citrix.com> -Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com> ---- -Changes since v2: -- s/_/-/; in command-line option -- Added __read_mostly ---- - docs/misc/xen-command-line.markdown | 15 +++++++++++++++ - xen/arch/x86/mm.c | 10 ++++++++++ - 2 files changed, 25 insertions(+) - -diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown -index 44d99852aa..45ef873abb 100644 ---- a/docs/misc/xen-command-line.markdown -+++ b/docs/misc/xen-command-line.markdown -@@ -1374,6 +1374,21 @@ The following resources are available: - CDP, one COS will corespond two CBMs other than one with CAT, due to the - sum of CBMs is fixed, that means actual `cos_max` in use will automatically - reduce to half when CDP is enabled. -+ -+### pv-linear-pt -+> `= <boolean>` -+ -+> Default: `false` -+ -+Allow PV guests to have pagetable entries pointing to other pagetables -+of the same level (i.e., allowing L2 PTEs to point to other L2 pages). -+This technique is often called "linear pagetables", and is sometimes -+used to allow operating systems a simple way to consistently map the -+current process's pagetables into its own virtual address space. -+ -+None of the most common PV operating systems (Linux, NetBSD, MiniOS) -+use this technique, but there may be custom operating systems which -+do. - - ### reboot - > `= t[riple] | k[bd] | a[cpi] | p[ci] | P[ower] | e[fi] | n[o] [, [w]arm | [c]old]` -diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c -index 1e469bd354..32952a46b9 100644 ---- a/xen/arch/x86/mm.c -+++ b/xen/arch/x86/mm.c -@@ -814,6 +814,9 @@ static void dec_linear_uses(struct page_info *pg) - * frame if it is mapped by a different root table. This is sufficient and - * also necessary to allow validation of a root table mapping itself. - */ -+static bool __read_mostly pv_linear_pt_enable = false; -+boolean_param("pv-linear-pt", pv_linear_pt_enable); -+ - #define define_get_linear_pagetable(level) \ - static int \ - get_##level##_linear_pagetable( \ -@@ -823,6 +826,13 @@ get_##level##_linear_pagetable( \ - struct page_info *page; \ - unsigned long pfn; \ - \ -+ if ( !pv_linear_pt_enable ) \ -+ { \ -+ gdprintk(XENLOG_WARNING, \ -+ "Attempt to create linear p.t. (feature disabled)\n"); \ -+ return 0; \ -+ } \ -+ \ - if ( (level##e_get_flags(pde) & _PAGE_RW) ) \ - { \ - gdprintk(XENLOG_WARNING, \ --- -2.14.1 - |