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, 83 insertions, 0 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 new file mode 100644 index 0000000000000..5e057c5652c11 --- /dev/null +++ b/system/xen/xsa/xsa240-4.9-0002-x86-mm-Disable-PV-linear-pagetables-by-default.patch @@ -0,0 +1,83 @@ +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 + |