On 2015/3/4 1:06, Petr Mladek wrote:
> On Tue 2015-03-03 13:09:05, Wang Nan wrote:
>> Before ftrace convertin instruction to nop, if an early kprobe is
>> registered then unregistered, without this patch its first bytes will
>> be replaced by head of NOP, which may confuse ftrace.
>>
>> Actually, since we have a patch which convert ftrace entry to nop
>> when probing, this problem should never be triggered. Provide it for
>> safety.
>>
>> Signed-off-by: Wang Nan <wangn...@huawei.com>
>> ---
>> arch/x86/kernel/kprobes/core.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
>> index 87beb64..c7d304d 100644
>> --- a/arch/x86/kernel/kprobes/core.c
>> +++ b/arch/x86/kernel/kprobes/core.c
>> @@ -225,6 +225,9 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned
>> long addr)
>> struct kprobe *kp;
>> unsigned long faddr;
>>
>> + if (!kprobes_on_ftrace_initialized)
>> + return addr;
>
> This is not correct. The function has to return a buffer with the original
> code also when it is modified by normal kprobes. If it is a normal
> Kprobe, it reads the current code and replaces the first byte (INT3
> instruction) with the saved kp->opcode.
>
>> +
>> kp = get_kprobe((void *)addr);
>> faddr = ftrace_location(addr);
>
> IMHO, the proper fix might be to replace the above line with
>
> if (kprobes_on_ftrace_initialized)
> faddr = ftrace_location(addr);
> else
> faddr = 0UL;
>
> By other words, it might pretend that it is not a ftrace location
> when the ftrace is not ready yet.
>
Thanks for your reply. I'll follow your suggection in my next version. I change
it as follow to enable the checking.
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 4e3d5a9..3241677 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -234,6 +234,20 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned long
addr)
*/
if (WARN_ON(faddr && faddr != addr))
return 0UL;
+
+ /*
+ * If ftrace is not ready yet, pretend this is not an ftrace
+ * location, because currently the target instruction has not
+ * been replaced by a NOP yet. When ftrace trying to convert
+ * it to NOP, kprobe should be notified and the kprobe data
+ * should be fixed at that time.
+ *
+ * Since it is possible that an early kprobe already on that
+ * place, don't return addr directly.
+ */
+ if (likely(kprobes_on_ftrace_initialized))
+ faddr = 0UL;
+
/*
* Use the current code if it is not modified by Kprobe
* and it cannot be modified by ftrace
> Or is the code modified another special way when it is a ftrace location but
> ftrace has not been initialized yet?
>
> Best Regards,
> Petr
>
>> /*
>> --
>> 1.8.4
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>> the body of a message to majord...@vger.kernel.org
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>> Please read the FAQ at http://www.tux.org/lkml/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
