[PATCH 8/7] uprobes/x86: Send SIGILL if arch_uprobe_post_xol() fails

[Oleg Nesterov]

Currently the error from arch_uprobe_post_xol() is silently ignored.
This doesn't look good and this can lead to the hard-to-debug problems.

1. Change handle_singlestep() to loudly complain and send SIGILL.

   Note: this only affects x86, ppc/arm can't fail.

2. Change arch_uprobe_post_xol() to call arch_uprobe_abort_xol() and
   avoid TF games if it is going to return an error.

   This can help to to analyze the problem, if nothing else we should
   not report ->ip = xol_slot in the core-file.

   Note: this means that handle_riprel_post_xol() can be called twice,
   but this is fine because it idempotent.

Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
 arch/x86/kernel/uprobes.c |   16 ++++++++++++----
 kernel/events/uprobes.c   |    8 +++++++-
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 43df132..3bdfb6e 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -594,6 +594,15 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, 
struct pt_regs *regs)
        struct uprobe_task *utask = current->utask;
 
        WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
+
+       if (auprobe->ops->post_xol) {
+               int err = auprobe->ops->post_xol(auprobe, regs);
+               if (err) {
+                       arch_uprobe_abort_xol(auprobe, regs);
+                       return err;
+               }
+       }
+
        current->thread.trap_nr = utask->autask.saved_trap_nr;
        /*
         * arch_uprobe_pre_xol() doesn't save the state of TIF_BLOCKSTEP
@@ -605,8 +614,6 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, 
struct pt_regs *regs)
        else if (!(auprobe->fixups & UPROBE_FIX_SETF))
                regs->flags &= ~X86_EFLAGS_TF;
 
-       if (auprobe->ops->post_xol)
-               return auprobe->ops->post_xol(auprobe, regs);
        return 0;
 }
 
@@ -641,8 +648,9 @@ int arch_uprobe_exception_notify(struct notifier_block 
*self, unsigned long val,
 
 /*
  * This function gets called when XOL instruction either gets trapped or
- * the thread has a fatal signal, so reset the instruction pointer to its
- * probed address.
+ * the thread has a fatal signal, or if arch_uprobe_post_xol() failed.
+ * Reset the instruction pointer to its probed address for the potential
+ * restart or for post mortem analysis.
  */
 void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 {
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 7a3e14e..2adbc97 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1858,10 +1858,11 @@ out:
 static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
 {
        struct uprobe *uprobe;
+       int err = 0;
 
        uprobe = utask->active_uprobe;
        if (utask->state == UTASK_SSTEP_ACK)
-               arch_uprobe_post_xol(&uprobe->arch, regs);
+               err = arch_uprobe_post_xol(&uprobe->arch, regs);
        else if (utask->state == UTASK_SSTEP_TRAPPED)
                arch_uprobe_abort_xol(&uprobe->arch, regs);
        else
@@ -1875,6 +1876,11 @@ static void handle_singlestep(struct uprobe_task *utask, 
struct pt_regs *regs)
        spin_lock_irq(&current->sighand->siglock);
        recalc_sigpending(); /* see uprobe_deny_signal() */
        spin_unlock_irq(&current->sighand->siglock);
+
+       if (unlikely(err)) {
+               uprobe_warn(current, "execute the probed insn, sending 
SIGILL.");
+               force_sig_info(SIGILL, SEND_SIG_FORCED, current);
+       }
 }
 
 /*
-- 
1.5.5.1


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/