kprobes: Prohibit probing on BUG() and WARN() address

Since BUG() and WARN() may use a trap (e.g. UD2 on x86) to
get the address where the BUG() has occurred, kprobes can not
do single-step out-of-line that instruction. So prohibit
probing on such address.

Without this fix, if someone put a kprobe on WARN(), the
kernel will crash with invalid opcode error instead of
outputing warning message, because kernel can not find
correct bug address.

Signed-off-by: Masami Hiramatsu <[e-mail]>
Acked-by: Steven Rostedt (VMware) <[e-mail]>
Acked-by: Naveen N. Rao <[e-mail]>
Cc: Anil S Keshavamurthy <[e-mail]>
Cc: David S . Miller <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Naveen N . Rao <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Link: https://lkml.kernel.org/r/156750890133.19112.3393666300746167111.stgit@devnote2
Signed-off-by: Ingo Molnar <[e-mail]>

include/linux/bug.h

···
 
 #else	/* !CONFIG_GENERIC_BUG */
 
+static inline void *find_bug(unsigned long bugaddr)
+{
+	return NULL;
+}
+
 static inline enum bug_trap_type report_bug(unsigned long bug_addr,
 					    struct pt_regs *regs)
 {

kernel/kprobes.c

···
 	/* Ensure it is not in reserved area nor out of text */
 	if (!kernel_text_address((unsigned long) p->addr) ||
 	    within_kprobe_blacklist((unsigned long) p->addr) ||
-	    jump_label_text_reserved(p->addr, p->addr)) {
+	    jump_label_text_reserved(p->addr, p->addr) ||
+	    find_bug((unsigned long)p->addr)) {
 		ret = -EINVAL;
 		goto out;
 	}