From 2cc42bac1c795f75fcc062b95c6ca7ac1b84d5d8 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Mon, 18 Dec 2017 09:37:45 -0700 Subject: [PATCH] x86-64/Xen: eliminate W+X mappings 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. Signed-off-by: Jan Beulich Reviewed-by: Juergen Gross Signed-off-by: Boris Ostrovsky --- arch/x86/xen/enlighten_pv.c | 3 +++ arch/x86/xen/mmu_pv.c | 12 ++++++++++++ 2 files changed, 15 insertions(+) diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c index 69b9deff7e5c..86f26ea99324 100644 --- a/arch/x86/xen/enlighten_pv.c +++ b/arch/x86/xen/enlighten_pv.c @@ -87,6 +87,8 @@ #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); @@ -1249,6 +1251,7 @@ asmlinkage __visible void __init xen_start_kernel(void) __userpte_alloc_gfp &= ~__GFP_HIGHMEM; /* Work out if we support NX */ + get_cpu_cap(&boot_cpu_data); x86_configure_nx(); /* Get mfn list */ diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c index 9d9cc3870722..7118f776cd49 100644 --- a/arch/x86/xen/mmu_pv.c +++ b/arch/x86/xen/mmu_pv.c @@ -1916,6 +1916,18 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) /* 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))