vdso: print fatal signals

Add the print-fatal-signals=1 boot option and the
/proc/sys/kernel/print-fatal-signals runtime switch.

This feature prints some minimal information about userspace segfaults to
the kernel console.  This is useful to find early bootup bugs where
userspace debugging is very hard.

Defaults to off.

[akpm@linux-foundation.org: Don't add new sysctl numbers]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index f9405609774e..39d122753bac 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -718,6 +718,37 @@ out_set:
 #define LEGACY_QUEUE(sigptr, sig) \
         (((sig) < SIGRTMIN) && sigismember(&(sigptr)->signal, (sig)))
 
+int print_fatal_signals;
+
+static void print_fatal_signal(struct pt_regs *regs, int signr)
+{
+        printk("%s/%d: potentially unexpected fatal signal %d.\n",
+                current->comm, current->pid, signr);
+
+#ifdef __i386__
+        printk("code at %08lx: ", regs->eip);
+        {
+                int i;
+                for (i = 0; i < 16; i++) {
+                        unsigned char insn;
+
+                        __get_user(insn, (unsigned char *)(regs->eip + i));
+                        printk("%02x ", insn);
+                }
+        }
+#endif
+        printk("\n");
+        show_regs(regs);
+}
+
+static int __init setup_print_fatal_signals(char *str)
+{
+        get_option (&str, &print_fatal_signals);
+
+        return 1;
+}
+
+__setup("print-fatal-signals=", setup_print_fatal_signals);
 
 static int
 specific_send_sig_info(int sig, struct siginfo *info, struct task_struct *t)
@@ -1855,6 +1886,8 @@ relock:
                  * Anything else is fatal, maybe with a core dump.
                  */
                 current->flags |= PF_SIGNALED;
+                if ((signr != SIGKILL) && print_fatal_signals)
+                        print_fatal_signal(regs, signr);
                 if (sig_kernel_coredump(signr)) {
                         /*
                          * If it was able to dump core, this kills all