Patch "x86/pti: Map the vsyscall page if needed" has been added to the 4.14-stable tree

[<gregkh@linuxfoundation.org>]

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

    x86/pti: Map the vsyscall page if needed

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-pti-map-the-vsyscall-page-if-needed.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 <stable@vger.kernel.org> know about it.


>From 85900ea51577e31b186e523c8f4e068c79ecc7d3 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@kernel.org>
Date: Tue, 12 Dec 2017 07:56:42 -0800
Subject: x86/pti: Map the vsyscall page if needed

From: Andy Lutomirski <luto@kernel.org>

commit 85900ea51577e31b186e523c8f4e068c79ecc7d3 upstream.

Make VSYSCALLs work fully in PTI mode by mapping them properly to the user
space visible page tables.

[ tglx: Hide unused functions (Patch by Arnd Bergmann) ]

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/entry/vsyscall/vsyscall_64.c |    6 +--
 arch/x86/include/asm/vsyscall.h       |    1 
 arch/x86/mm/pti.c                     |   65 ++++++++++++++++++++++++++++++++++
 3 files changed, 69 insertions(+), 3 deletions(-)

--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -344,14 +344,14 @@ int in_gate_area_no_mm(unsigned long add
  * vsyscalls but leave the page not present.  If so, we skip calling
  * this.
  */
-static void __init set_vsyscall_pgtable_user_bits(void)
+void __init set_vsyscall_pgtable_user_bits(pgd_t *root)
 {
 	pgd_t *pgd;
 	p4d_t *p4d;
 	pud_t *pud;
 	pmd_t *pmd;
 
-	pgd = pgd_offset_k(VSYSCALL_ADDR);
+	pgd = pgd_offset_pgd(root, VSYSCALL_ADDR);
 	set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));
 	p4d = p4d_offset(pgd, VSYSCALL_ADDR);
 #if CONFIG_PGTABLE_LEVELS >= 5
@@ -373,7 +373,7 @@ void __init map_vsyscall(void)
 			     vsyscall_mode == NATIVE
 			     ? PAGE_KERNEL_VSYSCALL
 			     : PAGE_KERNEL_VVAR);
-		set_vsyscall_pgtable_user_bits();
+		set_vsyscall_pgtable_user_bits(swapper_pg_dir);
 	}
 
 	BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -7,6 +7,7 @@
 
 #ifdef CONFIG_X86_VSYSCALL_EMULATION
 extern void map_vsyscall(void);
+extern void set_vsyscall_pgtable_user_bits(pgd_t *root);
 
 /*
  * Called on instruction fetch fault in vsyscall page.
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -38,6 +38,7 @@
 
 #include <asm/cpufeature.h>
 #include <asm/hypervisor.h>
+#include <asm/vsyscall.h>
 #include <asm/cmdline.h>
 #include <asm/pti.h>
 #include <asm/pgtable.h>
@@ -223,6 +224,69 @@ static pmd_t *pti_user_pagetable_walk_pm
 	return pmd_offset(pud, address);
 }
 
+#ifdef CONFIG_X86_VSYSCALL_EMULATION
+/*
+ * Walk the shadow copy of the page tables (optionally) trying to allocate
+ * page table pages on the way down.  Does not support large pages.
+ *
+ * Note: this is only used when mapping *new* kernel data into the
+ * user/shadow page tables.  It is never used for userspace data.
+ *
+ * Returns a pointer to a PTE on success, or NULL on failure.
+ */
+static __init pte_t *pti_user_pagetable_walk_pte(unsigned long address)
+{
+	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
+	pmd_t *pmd = pti_user_pagetable_walk_pmd(address);
+	pte_t *pte;
+
+	/* We can't do anything sensible if we hit a large mapping. */
+	if (pmd_large(*pmd)) {
+		WARN_ON(1);
+		return NULL;
+	}
+
+	if (pmd_none(*pmd)) {
+		unsigned long new_pte_page = __get_free_page(gfp);
+		if (!new_pte_page)
+			return NULL;
+
+		if (pmd_none(*pmd)) {
+			set_pmd(pmd, __pmd(_KERNPG_TABLE | __pa(new_pte_page)));
+			new_pte_page = 0;
+		}
+		if (new_pte_page)
+			free_page(new_pte_page);
+	}
+
+	pte = pte_offset_kernel(pmd, address);
+	if (pte_flags(*pte) & _PAGE_USER) {
+		WARN_ONCE(1, "attempt to walk to user pte\n");
+		return NULL;
+	}
+	return pte;
+}
+
+static void __init pti_setup_vsyscall(void)
+{
+	pte_t *pte, *target_pte;
+	unsigned int level;
+
+	pte = lookup_address(VSYSCALL_ADDR, &level);
+	if (!pte || WARN_ON(level != PG_LEVEL_4K) || pte_none(*pte))
+		return;
+
+	target_pte = pti_user_pagetable_walk_pte(VSYSCALL_ADDR);
+	if (WARN_ON(!target_pte))
+		return;
+
+	*target_pte = *pte;
+	set_vsyscall_pgtable_user_bits(kernel_to_user_pgdp(swapper_pg_dir));
+}
+#else
+static void __init pti_setup_vsyscall(void) { }
+#endif
+
 static void __init
 pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)
 {
@@ -319,4 +383,5 @@ void __init pti_init(void)
 	pti_clone_user_shared();
 	pti_clone_entry_text();
 	pti_setup_espfix64();
+	pti_setup_vsyscall();
 }


Patches currently in stable-queue which might be from luto@kernel.org are

queue-4.14/x86-mm-pti-allow-nx-poison-to-be-set-in-p4d-pgd.patch
queue-4.14/x86-dumpstack-indicate-in-oops-whether-pti-is-configured-and-enabled.patch
queue-4.14/x86-mm-clarify-the-whole-asid-kernel-pcid-user-pcid-naming.patch
queue-4.14/x86-mm-abstract-switching-cr3.patch
queue-4.14/x86-mm-optimize-restore_cr3.patch
queue-4.14/x86-mm-pti-force-entry-through-trampoline-when-pti-active.patch
queue-4.14/x86-entry-align-entry-text-section-to-pmd-boundary.patch
queue-4.14/x86-mm-64-make-a-full-pgd-entry-size-hole-in-the-memory-map.patch
queue-4.14/x86-cpu_entry_area-add-debugstore-entries-to-cpu_entry_area.patch
queue-4.14/x86-mm-pti-share-entry-text-pmd.patch
queue-4.14/x86-ldt-make-the-ldt-mapping-ro.patch
queue-4.14/x86-mm-dump_pagetables-check-user-space-page-table-for-wx-pages.patch
queue-4.14/x86-pti-map-the-vsyscall-page-if-needed.patch
queue-4.14/x86-mm-pti-disable-global-pages-if-page_table_isolation-y.patch
queue-4.14/x86-mm-dump_pagetables-allow-dumping-current-pagetables.patch
queue-4.14/x86-mm-pti-add-infrastructure-for-page-table-isolation.patch
queue-4.14/x86-cpufeatures-add-x86_bug_cpu_insecure.patch
queue-4.14/x86-mm-use-fix-pcid-to-optimize-user-kernel-switches.patch
queue-4.14/x86-mm-use-invpcid-for-__native_flush_tlb_single.patch
queue-4.14/x86-mm-pti-prepare-the-x86-entry-assembly-code-for-entry-exit-cr3-switching.patch
queue-4.14/x86-mm-allow-flushing-for-future-asid-switches.patch
queue-4.14/x86-mm-pti-add-kconfig.patch
queue-4.14/x86-mm-pti-add-mapping-helper-functions.patch
queue-4.14/x86-mm-pti-map-espfix-into-user-space.patch
queue-4.14/x86-mm-pti-share-cpu_entry_area-with-user-space-page-tables.patch
queue-4.14/x86-mm-pti-add-functions-to-clone-kernel-pmds.patch
queue-4.14/x86-pti-add-the-pti-cmdline-option-and-documentation.patch
queue-4.14/x86-events-intel-ds-map-debug-buffers-in-cpu_entry_area.patch
queue-4.14/x86-mm-pti-allocate-a-separate-user-pgd.patch
queue-4.14/x86-pti-put-the-ldt-in-its-own-pgd-if-pti-is-on.patch
queue-4.14/x86-mm-pti-populate-user-pgd.patch
queue-4.14/x86-mm-dump_pagetables-add-page-table-directory-to-the-debugfs-vfs-hierarchy.patch