This is a note to let you know that I've just added the patch titled
x86/ldt: Make the LDT mapping RO
to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: x86-ldt-make-the-ldt-mapping-ro.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 9f5cb6b32d9e0a3a7453222baaf15664d92adbf2 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner tglx@linutronix.de Date: Fri, 15 Dec 2017 20:35:11 +0100 Subject: x86/ldt: Make the LDT mapping RO
From: Thomas Gleixner tglx@linutronix.de
commit 9f5cb6b32d9e0a3a7453222baaf15664d92adbf2 upstream.
Now that the LDT mapping is in a known area when PAGE_TABLE_ISOLATION is enabled its a primary target for attacks, if a user space interface fails to validate a write address correctly. That can never happen, right?
The SDM states:
If the segment descriptors in the GDT or an LDT are placed in ROM, the processor can enter an indefinite loop if software or the processor attempts to update (write to) the ROM-based segment descriptors. To prevent this problem, set the accessed bits for all segment descriptors placed in a ROM. Also, remove operating-system or executive code that attempts to modify segment descriptors located in ROM.
So its a valid approach to set the ACCESS bit when setting up the LDT entry and to map the table RO. Fixup the selftest so it can handle that new mode.
Remove the manual ACCESS bit setter in set_tls_desc() as this is now pointless. Folded the patch from Peter Ziljstra.
Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Dave Hansen dave.hansen@linux.intel.com Cc: H. Peter Anvin hpa@zytor.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Juergen Gross jgross@suse.com 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/include/asm/desc.h | 2 ++ arch/x86/kernel/ldt.c | 7 ++++++- arch/x86/kernel/tls.c | 11 ++--------- tools/testing/selftests/x86/ldt_gdt.c | 3 +-- 4 files changed, 11 insertions(+), 12 deletions(-)
--- a/arch/x86/include/asm/desc.h +++ b/arch/x86/include/asm/desc.h @@ -21,6 +21,8 @@ static inline void fill_ldt(struct desc_
desc->type = (info->read_exec_only ^ 1) << 1; desc->type |= info->contents << 2; + /* Set the ACCESS bit so it can be mapped RO */ + desc->type |= 1;
desc->s = 1; desc->dpl = 0x3; --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -158,7 +158,12 @@ map_ldt_struct(struct mm_struct *mm, str ptep = get_locked_pte(mm, va, &ptl); if (!ptep) return -ENOMEM; - pte = pfn_pte(pfn, __pgprot(__PAGE_KERNEL & ~_PAGE_GLOBAL)); + /* + * Map it RO so the easy to find address is not a primary + * target via some kernel interface which misses a + * permission check. + */ + pte = pfn_pte(pfn, __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL)); set_pte_at(mm, va, ptep, pte); pte_unmap_unlock(ptep, ptl); } --- a/arch/x86/kernel/tls.c +++ b/arch/x86/kernel/tls.c @@ -93,17 +93,10 @@ static void set_tls_desc(struct task_str cpu = get_cpu();
while (n-- > 0) { - if (LDT_empty(info) || LDT_zero(info)) { + if (LDT_empty(info) || LDT_zero(info)) memset(desc, 0, sizeof(*desc)); - } else { + else fill_ldt(desc, info); - - /* - * Always set the accessed bit so that the CPU - * doesn't try to write to the (read-only) GDT. - */ - desc->type |= 1; - } ++info; ++desc; } --- a/tools/testing/selftests/x86/ldt_gdt.c +++ b/tools/testing/selftests/x86/ldt_gdt.c @@ -122,8 +122,7 @@ static void check_valid_segment(uint16_t * NB: Different Linux versions do different things with the * accessed bit in set_thread_area(). */ - if (ar != expected_ar && - (ldt || ar != (expected_ar | AR_ACCESSED))) { + if (ar != expected_ar && ar != (expected_ar | AR_ACCESSED)) { printf("[FAIL]\t%s entry %hu has AR 0x%08X but expected 0x%08X\n", (ldt ? "LDT" : "GDT"), index, ar, expected_ar); nerrs++;
Patches currently in stable-queue which might be from tglx@linutronix.de 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