[PATCH v6] [BUGFIX] kprobes: Fix "Failed to find blacklist" error on ia64 and ppc64

Masami Hiramatsu masami.hiramatsu.pt at hitachi.com
Thu Jul 17 21:44:11 EST 2014

On ia64 and ppc64, the function pointer does not point the
entry address of the function, but the address of function
discriptor (which contains the entry address and misc
data.) Since the kprobes passes the function pointer stored
by NOKPROBE_SYMBOL() to kallsyms_lookup_size_offset() for
initalizing its blacklist, it fails and reports many errors
as below.

  Failed to find blacklist 0001013168300000
  Failed to find blacklist 0001013000f0a000
  Failed to find blacklist 000101315f70a000
  Failed to find blacklist 000101324c80a000
  Failed to find blacklist 0001013063f0a000
  Failed to find blacklist 000101327800a000
  Failed to find blacklist 0001013277f0a000
  Failed to find blacklist 000101315a70a000
  Failed to find blacklist 0001013277e0a000
  Failed to find blacklist 000101305a20a000
  Failed to find blacklist 0001013277d0a000
  Failed to find blacklist 00010130bdc0a000
  Failed to find blacklist 00010130dc20a000
  Failed to find blacklist 000101309a00a000
  Failed to find blacklist 0001013277c0a000
  Failed to find blacklist 0001013277b0a000
  Failed to find blacklist 0001013277a0a000
  Failed to find blacklist 000101327790a000
  Failed to find blacklist 000101303140a000
  Failed to find blacklist 0001013a3280a000

To fix this bug, this uses arch_deref_entry_point() to get
the function entry address for kallsyms_lookup_size_offset()
instead of the raw function pointer.
Suzuki also pointed out that blacklist entries should also
be updated by that too.

Changes in v6:
 - Update patch description.
 - Remove "#include <linux/types.h>" which is no more needed
   because we don't use new function_entry() macro any more.

Changes in v5:
 - Use arch_deref_entry_point() instead of function_entry().

Changes in v4:
 - Add kernel_text_address() check for verifying the address.
 - Moved on the latest linus tree.

Changes in v3:
 - Fix a bug to get blacklist address based on function entry
   instead of function descriptor. (Suzuki's work, Thanks!)

Changes in V2:
 - Use function_entry() macro when lookin up symbols instead
   of storing it.
 - Update for the latest -next.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt at hitachi.com>
Fixed-by: Suzuki K. Poulose <suzuki at in.ibm.com>
Reported-by: Tony Luck <tony.luck at gmail.com>
Tested-by: Tony Luck <tony.luck at intel.com>
Tested-by: Michael Ellerman <mpe at ellerman.id.au>
Acked-by: Michael Ellerman <mpe at ellerman.id.au> (for powerpc)
Acked-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Fenghua Yu <fenghua.yu at intel.com>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Ananth N Mavinakayanahalli <ananth at in.ibm.com>
Cc: Kevin Hao <haokexin at gmail.com>
Cc: linux-ia64 at vger.kernel.org
Cc: linuxppc-dev at lists.ozlabs.org
 kernel/kprobes.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 3214289..734e9a7 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2037,19 +2037,23 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
 	unsigned long *iter;
 	struct kprobe_blacklist_entry *ent;
-	unsigned long offset = 0, size = 0;
+	unsigned long entry, offset = 0, size = 0;
 	for (iter = start; iter < end; iter++) {
-		if (!kallsyms_lookup_size_offset(*iter, &size, &offset)) {
-			pr_err("Failed to find blacklist %p\n", (void *)*iter);
+		entry = arch_deref_entry_point((void *)*iter);
+		if (!kernel_text_address(entry) ||
+		    !kallsyms_lookup_size_offset(entry, &size, &offset)) {
+			pr_err("Failed to find blacklist at %p\n",
+				(void *)entry);
 		ent = kmalloc(sizeof(*ent), GFP_KERNEL);
 		if (!ent)
 			return -ENOMEM;
-		ent->start_addr = *iter;
-		ent->end_addr = *iter + size;
+		ent->start_addr = entry;
+		ent->end_addr = entry + size;
 		list_add_tail(&ent->list, &kprobe_blacklist);

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