Re: [PATCH] kretprobe: avoid re-registration of the same kretprobe earlier
From: Wangshaobo (bobo)
Date: Wed Jan 13 2021 - 20:45:37 EST
I have found other problems when following Masami's proposals,
I have been dealing with other things this two days and i will send
patch as soon.
Thank you,
在 2021/1/14 8:25, Masami Hiramatsu 写道:
On Wed, 13 Jan 2021 17:48:45 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
Anything more on this?
I need Wangshaobo's confirmation, because this is essentially a kind of programming bug,
not a runtime bug. kprobes user must check the kprobe(kretprobe) must be unregistered
and cleaned up before reusing it. (I recommend to re-alloc new data structure each time)
For example, if you re-register your driver/filesystem without releasing, it will
break the kernel.
Thank you,
-- Steve
On Tue, 22 Dec 2020 20:03:56 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
On Mon, 21 Dec 2020 21:31:42 +0800
"Wangshaobo (bobo)" <bobo.shaobowang@xxxxxxxxxx> wrote:
Hi steven, Masami,
We have encountered a problem, when we attempted to use steven's suggestion as following,
If you call this here, you must make sure kprobe_addr() is called on rp->kp.
But if kretprobe_blacklist_size == 0, kprobe_addr() is not called before
this check. So it should be in between kprobe_on_func_entry() and
kretprobe_blacklist_size check, like this
if (!kprobe_on_func_entry(rp->kp.addr, rp->kp.symbol_name, rp->kp.offset))
return -EINVAL;
addr = kprobe_addr(&rp->kp);
if (IS_ERR(addr))
return PTR_ERR(addr);
rp->kp.addr = addr;
//there exists no-atomic operation risk, we should not modify any rp->kp's information, not all arch ensure atomic operation here.
ret = check_kprobe_rereg(&rp->kp);
if (WARN_ON(ret))
return ret;
if (kretprobe_blacklist_size) {
for (i = 0; > > + ret = check_kprobe_rereg(&rp->kp);
it returns failure from register_kprobe() end called by register_kretprobe() when
we registered a kretprobe through .symbol_name at first time(through .addr is OK),
kprobe_addr() called at the begaining of register_kprobe() will recheck and
failed at following place because at this time we symbol_name is not NULL and addr is also.
Good catch! Yes, it will reject if both kp->addr and kp->symbol are set.
static kprobe_opcode_t *_kprobe_addr(const char *symbol_name,
unsigned int offset)
{
if ((symbol_name && addr) || (!symbol_name && !addr)) //we failed here
So we attempted to move this sentence rp->kp.addr = addr to __get_valid_kprobe() like this to
avoid explict usage of rp->kp.addr = addr in register_kretprobe().
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index dd5821f753e6..ea014779edfe 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1502,10 +1502,15 @@ static kprobe_opcode_t *kprobe_addr(struct kprobe *p)
static struct kprobe *__get_valid_kprobe(struct kprobe *p)
{
struct kprobe *ap, *list_p;
+ void *addr;
lockdep_assert_held(&kprobe_mutex);
- ap = get_kprobe(p->addr);
+ addr = kprobe_addr(p);
+ if (IS_ERR(addr))
+ return NULL;
+
+ ap = get_kprobe(addr);
if (unlikely(!ap))
return NULL;
But it also failed when we second time attempted to register a same kretprobe, it is also
becasue symbol_name and addr is not NULL when we used __get_valid_kprobe().
What the "second time" means? If you reuse the kretprobe (and kprobe) you must
reset (cleanup) the kp->addr or kp->symbol_name. That is the initial state.
I think the API should not allow users to enter inconsistent information.
So it seems has no idea expect for modifying _kprobe_addr() like following this, the reason is that
the patch 0bd476e6c671 ("kallsyms: unexport kallsyms_lookup_name() and kallsyms_on_each_symbol()")
has telled us we'd better use symbol name to register but not address anymore.
-static kprobe_opcode_t *_kprobe_addr(kprobe_opcode_t *addr,
- const char *symbol_name, unsigned int offset)
+static kprobe_opcode_t *_kprobe_addr(const char *symbol_name,
+ unsigned int offset)
{
- if ((symbol_name && addr) || (!symbol_name && !addr))
+ kprobe_opcode_t *addr;
+ if (!symbol_name)
goto invalid;
No, there are cases that the user will set only kp->addr, but no kp->symbol_name.
For us, this modification has not caused a big impact on other modules, only expects a little
influence on bpf from calling trace_kprobe_on_func_entry(), it can not use addr to fill in
rp.kp in struct trace_event_call anymore.
So i want to know your views, and i will resend this patch soon.
OK, I think it is simpler to check the rp->kp.addr && rp->kp.symbol_name
because it is not allowed (it can lead inconsistent setting).
How about this code? Is this work for you?
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 41fdbb7953c6..73500be564be 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2103,6 +2103,14 @@ int register_kretprobe(struct kretprobe *rp)
int i;
void *addr;
+ /* It is not allowed to specify addr and symbol_name at the same time */
+ if (rp->kp.addr && rp->kp.symbol_name)
+ return -EINVAL;
+
+ /* If only rp->kp.addr is specified, check reregistering kprobes */
+ if (rp->kp.addr && check_kprobe_rereg(&rp->kp))
+ return -EINVAL;
+
if (!kprobe_on_func_entry(rp->kp.addr, rp->kp.symbol_name, rp->kp.offset))
return -EINVAL;
Thank you,