[tip:perf/core] kprobes/x86: Just return error for sanity check failure instead of using BUG_ON

[tip-bot for Masami Hiramatsu <tipbot@zytor.com>]

Commit-ID:  8101376dc5f42bd93b36d4ab210b44503d0ec11f
Gitweb:     http://git.kernel.org/tip/8101376dc5f42bd93b36d4ab210b44503d0ec11f
Author:     Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
AuthorDate: Thu, 4 Apr 2013 19:42:30 +0900
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 8 Apr 2013 17:28:34 +0200

kprobes/x86: Just return error for sanity check failure instead of using BUG_ON

Return an error from __copy_instruction() and use printk() to
give us a more productive message, since this is just an error
case which we can handle and also the BUG_ON() never tells us
why and what happened.

This is related to the following bug-report:

   https://bugzilla.redhat.com/show_bug.cgi?id=910649

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Frank Ch. Eigler <fche@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: yrl.pp-manager.tt@hitachi.com
Link: http://lkml.kernel.org/r/20130404104230.22862.85242.stgit@mhiramat-M0-7522
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/kprobes/core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 7bfe318..9895a9a 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -353,7 +353,11 @@ int __kprobes __copy_instruction(u8 *dest, u8 *src)
 		 * have given.
 		 */
 		newdisp = (u8 *) src + (s64) insn.displacement.value - (u8 *) dest;
-		BUG_ON((s64) (s32) newdisp != newdisp); /* Sanity check.  */
+		if ((s64) (s32) newdisp != newdisp) {
+			pr_err("Kprobes error: new displacement does not fit into s32 (%llx)\n", newdisp);
+			pr_err("\tSrc: %p, Dest: %p, old disp: %x\n", src, dest, insn.displacement.value);
+			return 0;
+		}
 		disp = (u8 *) dest + insn_offset_displacement(&insn);
 		*(s32 *) disp = (s32) newdisp;
 	}