Patch "x86/entry/64: Fix CR3 restore in paranoid_exit()" has been added to the 4.15-stable tree

[<gregkh@linuxfoundation.org>]

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

    x86/entry/64: Fix CR3 restore in paranoid_exit()

to the 4.15-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-entry-64-fix-cr3-restore-in-paranoid_exit.patch
and it can be found in the queue-4.15 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 e48657573481a5dff7cfdc3d57005c80aa816500 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@kernel.org>
Date: Wed, 14 Feb 2018 08:39:11 +0100
Subject: x86/entry/64: Fix CR3 restore in paranoid_exit()

From: Ingo Molnar <mingo@kernel.org>

commit e48657573481a5dff7cfdc3d57005c80aa816500 upstream.

Josh Poimboeuf noticed the following bug:

 "The paranoid exit code only restores the saved CR3 when it switches back
  to the user GS.  However, even in the kernel GS case, it's possible that
  it needs to restore a user CR3, if for example, the paranoid exception
  occurred in the syscall exit path between SWITCH_TO_USER_CR3_STACK and
  SWAPGS."

Josh also confirmed via targeted testing that it's possible to hit this bug.

Fix the bug by also restoring CR3 in the paranoid_exit_no_swapgs branch.

The reason we haven't seen this bug reported by users yet is probably because
"paranoid" entry points are limited to the following cases:

 idtentry double_fault       do_double_fault  has_error_code=1  paranoid=2
 idtentry debug              do_debug         has_error_code=0  paranoid=1 shift_ist=DEBUG_STACK
 idtentry int3               do_int3          has_error_code=0  paranoid=1 shift_ist=DEBUG_STACK
 idtentry machine_check      do_mce           has_error_code=0  paranoid=1

Amongst those entry points only machine_check is one that will interrupt an
IRQS-off critical section asynchronously - and machine check events are rare.

The other main asynchronous entries are NMI entries, which can be very high-freq
with perf profiling, but they are special: they don't use the 'idtentry' macro but
are open coded and restore user CR3 unconditionally so don't have this bug.

Reported-and-tested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180214073910.boevmg65upbk3vqb@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/entry/entry_64.S |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1168,6 +1168,7 @@ ENTRY(paranoid_exit)
 	jmp	.Lparanoid_exit_restore
 .Lparanoid_exit_no_swapgs:
 	TRACE_IRQS_IRETQ_DEBUG
+	RESTORE_CR3	scratch_reg=%rbx save_reg=%r14
 .Lparanoid_exit_restore:
 	jmp restore_regs_and_return_to_kernel
 END(paranoid_exit)


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

queue-4.15/selftests-x86-fix-build-bug-caused-by-the-5lvl-test-which-has-been-moved-to-the-vm-directory.patch
queue-4.15/x86-entry-64-interleave-xor-register-clearing-with-push-instructions.patch
queue-4.15/x86-spectre-fix-an-error-message.patch
queue-4.15/nospec-move-array_index_nospec-parameter-checking-into-separate-macro.patch
queue-4.15/x86-entry-64-merge-the-pop_c_regs-and-pop_extra_regs-macros-into-a-single-pop_regs-macro.patch
queue-4.15/x86-gpu-add-cfl-to-early-quirks.patch
queue-4.15/x86-entry-64-remove-the-unused-icebp-macro.patch
queue-4.15/kvm-nvmx-set-the-cpu_based_use_msr_bitmaps-if-we-have-a-valid-l02-msr-bitmap.patch
queue-4.15/x86-nvmx-properly-set-spec_ctrl-and-pred_cmd-before-merging-msrs.patch
queue-4.15/x86-speculation-add-asm-msr-index.h-dependency.patch
queue-4.15/x86-entry-64-use-push_and_clean_regs-in-more-cases.patch
queue-4.15/x86-cpu-rename-cpu_data.x86_mask-to-cpu_data.x86_stepping.patch
queue-4.15/selftests-x86-disable-tests-requiring-32-bit-support-on-pure-64-bit-systems.patch
queue-4.15/x86-debug-use-ud2-for-warn.patch
queue-4.15/x86-entry-64-fix-paranoid_entry-frame-pointer-warning.patch
queue-4.15/x86-cpu-change-type-of-x86_cache_size-variable-to-unsigned-int.patch
queue-4.15/x86-speculation-update-speculation-control-microcode-blacklist.patch
queue-4.15/x86-entry-64-clear-registers-for-exceptions-interrupts-to-reduce-speculation-attack-surface.patch
queue-4.15/x86-speculation-correct-speculation-control-microcode-blacklist-again.patch
queue-4.15/x86-entry-64-merge-save_c_regs-and-save_extra_regs-remove-unused-extensions.patch
queue-4.15/selftests-x86-do-not-rely-on-int-0x80-in-single_step_syscall.c.patch
queue-4.15/selftests-x86-mpx-fix-incorrect-bounds-with-old-_sigfault.patch
queue-4.15/selftests-x86-fix-vdso-selftest-segfault-for-vsyscall-none.patch
queue-4.15/x86-debug-objtool-annotate-warn-related-ud2-as-reachable.patch
queue-4.15/objtool-fix-segfault-in-ignore_unreachable_insn.patch
queue-4.15/x86-entry-64-indent-push_and_clear_regs-and-pop_regs-properly.patch
queue-4.15/selftests-x86-pkeys-remove-unused-functions.patch
queue-4.15/selftests-x86-clean-up-and-document-sscanf-usage.patch
queue-4.15/x86-speculation-fix-up-array_index_nospec_mask-asm-constraint.patch
queue-4.15/x86-entry-64-clear-extra-registers-beyond-syscall-arguments-to-reduce-speculation-attack-surface.patch
queue-4.15/kvm-x86-reduce-retpoline-performance-impact-in-slot_handle_level_range-by-always-inlining-iterator-helper-methods.patch
queue-4.15/selftests-x86-do-not-rely-on-int-0x80-in-test_mremap_vdso.c.patch
queue-4.15/x86-mm-pti-fix-pti-comment-in-entry_syscall_64.patch
queue-4.15/x86-entry-64-get-rid-of-the-alloc_pt_gpregs_on_stack-and-save_and_clear_regs-macros.patch
queue-4.15/x86-speculation-clean-up-various-spectre-related-details.patch
queue-4.15/x86-kexec-make-kexec-mostly-work-in-5-level-paging-mode.patch
queue-4.15/x86-entry-64-introduce-the-push_and_clean_regs-macro.patch
queue-4.15/revert-x86-speculation-simplify-indirect_branch_prediction_barrier.patch
queue-4.15/x86-entry-64-compat-clear-registers-for-compat-syscalls-to-reduce-speculation-attack-surface.patch
queue-4.15/x86-mm-rename-flush_tlb_single-and-flush_tlb_one-to-__flush_tlb_one_.patch
queue-4.15/x86-entry-64-fix-cr3-restore-in-paranoid_exit.patch