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

[Petr Mladek <pmladek@suse.cz>]

__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@hitachi.com>
Signed-off-by: Petr Mladek <pmladek@suse.cz>
---
 arch/x86/kernel/kprobes/core.c | 6 ++++++
 1 file changed, 6 insertions(+)


This is follow up for the patch ("[PATCH v2] kprobes/x86: Use 5-byte NOP
when the code might be modified by ftrace") based on the Masami's
suggestion, see https://lkml.org/lkml/2015/2/3/207

Let me know if I should merge this with the first patch and send v3.


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.
 	 */
-- 
1.8.5.6