Messages in this thread | | | Subject | Re: [PATCH] kretprobe: avoid re-registration of the same kretprobe earlier | From | "Wangshaobo (bobo)" <> | Date | Thu, 14 Jan 2021 09:06:36 +0800 |
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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@goodmis.org> 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@kernel.org> wrote: >> >>> On Mon, 21 Dec 2020 21:31:42 +0800 >>> "Wangshaobo (bobo)" <bobo.shaobowang@huawei.com> 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, >>> >
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