x86/jump-label: Show where and what was wrong on errors

When modifying text sections for jump labels, a paranoid check is
performed. If the check fails, the system "bugs". But why it failed
is not shown.

The BUG_ON()s in the jump label update code is replaced with bug_at(ip).
This is a function that will show what pointer failed, and what was
at the location of the failure that made jump label panic.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index 24cf2b2..912a528 100644 (file)
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -24,6 +24,18 @@ union jump_code_union {
        } __attribute__((packed));
 };
 
+static void bug_at(unsigned char *ip, int line)
+{
+       /*
+        * The location is not an op that we were expecting.
+        * Something went wrong. Crash the box, as something could be
+        * corrupting the kernel.
+        */
+       pr_warning("Unexpected op at %pS [%p] (%02x %02x %02x %02x %02x) %s:%d\n",
+              ip, ip, ip[0], ip[1], ip[2], ip[3], ip[4], __FILE__, line);
+       BUG();
+}
+
 static void __jump_label_transform(struct jump_entry *entry,
                                   enum jump_label_type type,
                                   void *(*poker)(void *, const void *, size_t),
@@ -37,7 +49,8 @@ static void __jump_label_transform(struct jump_entry *entry,
                 * We are enabling this jump label. If it is not a nop
                 * then something must have gone wrong.
                 */
-               BUG_ON(memcmp((void *)entry->code, ideal_nop, 5) != 0);
+               if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0))
+                       bug_at((void *)entry->code, __LINE__);
 
                code.jump = 0xe9;
                code.offset = entry->target -
@@ -51,12 +64,14 @@ static void __jump_label_transform(struct jump_entry *entry,
                 */
                if (init) {
                        const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
-                       BUG_ON(memcmp((void *)entry->code, default_nop, 5) != 0);
+                       if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
+                               bug_at((void *)entry->code, __LINE__);
                } else {
                        code.jump = 0xe9;
                        code.offset = entry->target -
                                (entry->code + JUMP_LABEL_NOP_SIZE);
-                       BUG_ON(memcmp((void *)entry->code, &code, 5) != 0);
+                       if (unlikely(memcmp((void *)entry->code, &code, 5) != 0))
+                               bug_at((void *)entry->code, __LINE__);
                }
                memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
        }