releases/3.18.85/powerpc-signal-properly-handle-return-value-from-uprobe_deny_signal.patch

   1 From 46725b17f1c6c815a41429259b3f070c01e71bc1 Mon Sep 17 00:00:00 2001
   2 From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
   3 Date: Thu, 31 Aug 2017 21:55:57 +0530
   4 Subject: powerpc/signal: Properly handle return value from uprobe_deny_signal()
   5
   6 From: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
   7
   8 commit 46725b17f1c6c815a41429259b3f070c01e71bc1 upstream.
   9
  10 When a uprobe is installed on an instruction that we currently do not
  11 emulate, we copy the instruction into a xol buffer and single step
  12 that instruction. If that instruction generates a fault, we abort the
  13 single stepping before invoking the signal handler. Once the signal
  14 handler is done, the uprobe trap is hit again since the instruction is
  15 retried and the process repeats.
  16
  17 We use uprobe_deny_signal() to detect if the xol instruction triggered
  18 a signal. If so, we clear TIF_SIGPENDING and set TIF_UPROBE so that the
  19 signal is not handled until after the single stepping is aborted. In
  20 this case, uprobe_deny_signal() returns true and get_signal() ends up
  21 returning 0. However, in do_signal(), we are not looking at the return
  22 value, but depending on ksig.sig for further action, all with an
  23 uninitialized ksig that is not touched in this scenario. Fix the same
  24 by initializing ksig.sig to 0.
  25
  26 Fixes: 129b69df9c90 ("powerpc: Use get_signal() signal_setup_done()")
  27 Reported-by: Anton Blanchard <anton@samba.org>
  28 Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
  29 Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
  30 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  31
  32 ---
  33  arch/powerpc/kernel/signal.c |    2 +-
  34  1 file changed, 1 insertion(+), 1 deletion(-)
  35
  36 --- a/arch/powerpc/kernel/signal.c
  37 +++ b/arch/powerpc/kernel/signal.c
  38 @@ -102,7 +102,7 @@ static void check_syscall_restart(struct
  39  static void do_signal(struct pt_regs *regs)
  40  {
  41         sigset_t *oldset = sigmask_to_save();
  42 -       struct ksignal ksig;
  43 +       struct ksignal ksig = { .sig = 0 };
  44         int ret;
  45         int is32 = is_32bit_task();
  46