releases/4.14.108/arm64-debug-ensure-debug-handlers-check-triggering-exception-level.patch

   1 From 6bd288569b50bc89fa5513031086746968f585cb Mon Sep 17 00:00:00 2001
   2 From: Will Deacon <will.deacon@arm.com>
   3 Date: Fri, 1 Mar 2019 13:28:01 +0000
   4 Subject: arm64: debug: Ensure debug handlers check triggering exception level
   5
   6 From: Will Deacon <will.deacon@arm.com>
   7
   8 commit 6bd288569b50bc89fa5513031086746968f585cb upstream.
   9
  10 Debug exception handlers may be called for exceptions generated both by
  11 user and kernel code. In many cases, this is checked explicitly, but
  12 in other cases things either happen to work by happy accident or they
  13 go slightly wrong. For example, executing 'brk #4' from userspace will
  14 enter the kprobes code and be ignored, but the instruction will be
  15 retried forever in userspace instead of delivering a SIGTRAP.
  16
  17 Fix this issue in the most stable-friendly fashion by simply adding
  18 explicit checks of the triggering exception level to all of our debug
  19 exception handlers.
  20
  21 Cc: <stable@vger.kernel.org>
  22 Reviewed-by: Mark Rutland <mark.rutland@arm.com>
  23 Signed-off-by: Will Deacon <will.deacon@arm.com>
  24 Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
  25 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  26
  27 ---
  28  arch/arm64/kernel/kgdb.c           |   14 ++++++++++----
  29  arch/arm64/kernel/probes/kprobes.c |    6 ++++++
  30  2 files changed, 16 insertions(+), 4 deletions(-)
  31
  32 --- a/arch/arm64/kernel/kgdb.c
  33 +++ b/arch/arm64/kernel/kgdb.c
  34 @@ -233,27 +233,33 @@ int kgdb_arch_handle_exception(int excep
  35
  36  static int kgdb_brk_fn(struct pt_regs *regs, unsigned int esr)
  37  {
  38 +       if (user_mode(regs))
  39 +               return DBG_HOOK_ERROR;
  40 +
  41         kgdb_handle_exception(1, SIGTRAP, 0, regs);
  42 -       return 0;
  43 +       return DBG_HOOK_HANDLED;
  44  }
  45  NOKPROBE_SYMBOL(kgdb_brk_fn)
  46
  47  static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int esr)
  48  {
  49 +       if (user_mode(regs))
  50 +               return DBG_HOOK_ERROR;
  51 +
  52         compiled_break = 1;
  53         kgdb_handle_exception(1, SIGTRAP, 0, regs);
  54
  55 -       return 0;
  56 +       return DBG_HOOK_HANDLED;
  57  }
  58  NOKPROBE_SYMBOL(kgdb_compiled_brk_fn);
  59
  60  static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr)
  61  {
  62 -       if (!kgdb_single_step)
  63 +       if (user_mode(regs) || !kgdb_single_step)
  64                 return DBG_HOOK_ERROR;
  65
  66         kgdb_handle_exception(1, SIGTRAP, 0, regs);
  67 -       return 0;
  68 +       return DBG_HOOK_HANDLED;
  69  }
  70  NOKPROBE_SYMBOL(kgdb_step_brk_fn);
  71
  72 --- a/arch/arm64/kernel/probes/kprobes.c
  73 +++ b/arch/arm64/kernel/probes/kprobes.c
  74 @@ -458,6 +458,9 @@ kprobe_single_step_handler(struct pt_reg
  75         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  76         int retval;
  77
  78 +       if (user_mode(regs))
  79 +               return DBG_HOOK_ERROR;
  80 +
  81         /* return error if this is not our step */
  82         retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
  83
  84 @@ -474,6 +477,9 @@ kprobe_single_step_handler(struct pt_reg
  85  int __kprobes
  86  kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
  87  {
  88 +       if (user_mode(regs))
  89 +               return DBG_HOOK_ERROR;
  90 +
  91         kprobe_handler(regs);
  92         return DBG_HOOK_HANDLED;
  93  }