Messages in this thread Patch in this message | | | Subject | Re: [PATCH] kretprobe: avoid re-registration of the same kretprobe earlier | From | "Wangshaobo (bobo)" <> | Date | Mon, 21 Dec 2020 21:31:42 +0800 |
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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.
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(). 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; 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.
thanks, Wang Shaobo
>>> >
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