[PATCH 4/4] x86/jump-label: Show where and what was wrong on errors

Steven Rostedt
2013-08-07T16:51:18Z

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From: Steven Rostedt <srostedt@redhat.com>

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>
---
arch/x86/kernel/jump_label.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index 24cf2b2..912a528 100644
--- 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);
}
--
1.7.10.4