releases/4.14.117/arm64-only-advance-singlestep-for-user-instruction-traps.patch

   1 From 9478f1927e6ef9ef5e1ad761af1c98aa8e40b7f5 Mon Sep 17 00:00:00 2001
   2 From: Mark Rutland <mark.rutland@arm.com>
   3 Date: Tue, 3 Apr 2018 11:22:51 +0100
   4 Subject: arm64: only advance singlestep for user instruction traps
   5
   6 From: Mark Rutland <mark.rutland@arm.com>
   7
   8 commit 9478f1927e6ef9ef5e1ad761af1c98aa8e40b7f5 upstream.
   9
  10 Our arm64_skip_faulting_instruction() helper advances the userspace
  11 singlestep state machine, but this is also called by the kernel BRK
  12 handler, as used for WARN*().
  13
  14 Thus, if we happen to hit a WARN*() while the user singlestep state
  15 machine is in the active-no-pending state, we'll advance to the
  16 active-pending state without having executed a user instruction, and
  17 will take a step exception earlier than expected when we return to
  18 userspace.
  19
  20 Let's fix this by only advancing the state machine when skipping a user
  21 instruction.
  22
  23 Signed-off-by: Mark Rutland <mark.rutland@arm.com>
  24 Cc: Andrey Konovalov <andreyknvl@google.com>
  25 Cc: Catalin Marinas <catalin.marinas@arm.com>
  26 Cc: Will Deacon <will.deacon@arm.com>
  27 Signed-off-by: Will Deacon <will.deacon@arm.com>
  28 Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
  29 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  30
  31 ---
  32  arch/arm64/kernel/traps.c |    3 ++-
  33  1 file changed, 2 insertions(+), 1 deletion(-)
  34
  35 --- a/arch/arm64/kernel/traps.c
  36 +++ b/arch/arm64/kernel/traps.c
  37 @@ -304,7 +304,8 @@ void arm64_skip_faulting_instruction(str
  38          * If we were single stepping, we want to get the step exception after
  39          * we return from the trap.
  40          */
  41 -       user_fastforward_single_step(current);
  42 +       if (user_mode(regs))
  43 +               user_fastforward_single_step(current);
  44  }
  45
  46  static LIST_HEAD(undef_hook);