Patch "x86-64/Xen: eliminate W+X mappings" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

x86-64/Xen: eliminate W+X mappings

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     x86-64-xen-eliminate-w-x-mappings.patch

and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Beulich <[email protected]>
Date: Mon, 18 Dec 2017 09:37:45 -0700
Subject: x86-64/Xen: eliminate W+X mappings

From: Jan Beulich <[email protected]>

[ Upstream commit 2cc42bac1c795f75fcc062b95c6ca7ac1b84d5d8 ]

A few thousand such pages are usually left around due to the re-use of L1 tables having been provided by the hypervisor (Dom0) or tool stack (DomU). Set NX in the direct map variant, which needs to be done in L2 due to the dual use of the re-used L1s.

For x86_configure_nx() to actually do what it is supposed to do, call get_cpu_cap() first. This was broken by commit 4763ed4d45 ("x86, mm:
Clean up and simplify NX enablement") when switching away from the direct EFER read.

---
 arch/x86/xen/enlighten_pv.c |    3 +++
 arch/x86/xen/mmu_pv.c       |   12 ++++++++++++
 2 files changed, 15 insertions(+)

@@ -88,6 +88,8 @@
 #include "multicalls.h"
 #include "pmu.h"
 
+#include "../kernel/cpu/cpu.h" /* get_cpu_cap() */
+
 void *xen_initial_gdt;
 
 static int xen_cpu_up_prepare_pv(unsigned int cpu);

@@ -1257,6 +1259,7 @@ asmlinkage __visible void __init xen_sta
 	__userpte_alloc_gfp &= ~__GFP_HIGHMEM;
 
 	/* Work out if we support NX */
+	get_cpu_cap(&boot_cpu_data);
 	x86_configure_nx();
 
 	/* Get mfn list */

@@ -1902,6 +1902,18 @@ void __init xen_setup_kernel_pagetable(p
 	/* Graft it onto L4[511][510] */
 	copy_page(level2_kernel_pgt, l2);
 
+	/*
+	 * Zap execute permission from the ident map. Due to the sharing of
+	 * L1 entries we need to do this in the L2.
+	 */
+	if (__supported_pte_mask & _PAGE_NX) {
+		for (i = 0; i < PTRS_PER_PMD; ++i) {
+			if (pmd_none(level2_ident_pgt[i]))
+				continue;
+			level2_ident_pgt[i] = pmd_set_flags(level2_ident_pgt[i], _PAGE_NX);
+		}
+	}
+
 	/* Copy the initial P->M table mappings if necessary. */
 	i = pgd_index(xen_start_info->mfn_list);
 	if (i && i < pgd_index(__START_KERNEL_map))

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/x86-64-xen-eliminate-w-x-mappings.patch