[PATCH 2/2] kprobes/x86: Check for invalid ftrace location in __recover_probed_insn()

From: Petr Mladek
Date: Fri Feb 20 2015 - 05:16:39 EST

__recover_probed_insn() should always be called from an address where
an instructions starts. The check for ftrace_location() might help to
discover a potential inconsistency. Something goes terribly wrong when
an address inside the ftrace location is checked. Let's BUG() in this case.

Suggested-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Signed-off-by: Petr Mladek <pmladek@xxxxxxx>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
arch/x86/kernel/kprobes/core.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 2f464b56766a..124577dcf768 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -228,6 +228,12 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
kp = get_kprobe((void *)addr);
faddr = ftrace_location(addr);
+ * Addresses inside the ftrace location are refused by
+ * arch_check_ftrace_location(). Something went terribly wrong
+ * if such an address is checked here.
+ */
+ BUG_ON(faddr && faddr != addr);
+ /*
* Use the current code if it is not modified by Kprobe
* and it cannot be modified by ftrace.

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