Add arch_ptrace_stop

This adds support to allow asm/ptrace.h to define two new macros,
arch_ptrace_stop_needed and arch_ptrace_stop.  These control special
machine-specific actions to be done before a ptrace stop.  The new code
compiles away to nothing when the new macros are not defined.  This is the
case on all machines to begin with.

On ia64, these macros will be defined to solve the long-standing issue of
ptrace vs register backing store.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Petr Tesarik <ptesarik@suse.cz>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Matthew Wilcox <willy@debian.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 32 insertions, 1 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index e46971560fcb..5d30ff561847 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1578,6 +1578,17 @@ static inline int may_ptrace_stop(void)
 }
 
 /*
+ * Return nonzero if there is a SIGKILL that should be waking us up.
+ * Called with the siglock held.
+ */
+static int sigkill_pending(struct task_struct *tsk)
+{
+        return ((sigismember(&tsk->pending.signal, SIGKILL) ||
+                 sigismember(&tsk->signal->shared_pending.signal, SIGKILL)) &&
+                !unlikely(sigismember(&tsk->blocked, SIGKILL)));
+}
+
+/*
  * This must be called with current->sighand->siglock held.
  *
  * This should be the path for all ptrace stops.
@@ -1590,6 +1601,26 @@ static inline int may_ptrace_stop(void)
  */
 static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
 {
+        int killed = 0;
+
+        if (arch_ptrace_stop_needed(exit_code, info)) {
+                /*
+                 * The arch code has something special to do before a
+                 * ptrace stop.  This is allowed to block, e.g. for faults
+                 * on user stack pages.  We can't keep the siglock while
+                 * calling arch_ptrace_stop, so we must release it now.
+                 * To preserve proper semantics, we must do this before
+                 * any signal bookkeeping like checking group_stop_count.
+                 * Meanwhile, a SIGKILL could come in before we retake the
+                 * siglock.  That must prevent us from sleeping in TASK_TRACED.
+                 * So after regaining the lock, we must check for SIGKILL.
+                 */
+                spin_unlock_irq(&current->sighand->siglock);
+                arch_ptrace_stop(exit_code, info);
+                spin_lock_irq(&current->sighand->siglock);
+                killed = sigkill_pending(current);
+        }
+
         /*
          * If there is a group stop in progress,
          * we must participate in the bookkeeping.
@@ -1605,7 +1636,7 @@ static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
         spin_unlock_irq(&current->sighand->siglock);
         try_to_freeze();
         read_lock(&tasklist_lock);
-        if (may_ptrace_stop()) {
+        if (!unlikely(killed) && may_ptrace_stop()) {
                 do_notify_parent_cldstop(current, CLD_TRAPPED);
                 read_unlock(&tasklist_lock);
                 schedule();