Messages in this thread | | | Date | Thu, 10 Jun 2021 19:16:43 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH] kprobes: Print an error if probe is rejected |
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Hi Naveen,
On Thu, 10 Jun 2021 14:26:17 +0530 "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
> When probing at different locations in the kernel, it is not always > evident if the location can be probed or not. As an example: > > $ perf probe __radix__flush_tlb_range:35 > Failed to write event: Invalid argument > Error: Failed to add events. > > The probed line above is: > 35 if (!mmu_has_feature(MMU_FTR_GTSE) && type == FLUSH_TYPE_GLOBAL) { > > This ends up trying to probe on BUILD_BUG_ON(), which is rejected. > However, the user receives no indication at all as to why the probe > failed. Print an error in such cases so that it is clear that the probe > was rejected.
Hmm, Nack for this way, but I understand that is a problem. If you got the error in perf probe, which uses ftrace dynamic-event interface. In that case, the errors should not be output in the dmesg, but are reported via error_log in tracefs. And kprobes itself should return different error code to the caller, instead of printing error in dmesg. See below.
[...] > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -1542,8 +1542,10 @@ static int check_kprobe_address_safe(struct kprobe *p, > int ret; > > ret = arch_check_ftrace_location(p); > - if (ret) > + if (ret) { > + pr_err("kprobes: can't probe at the provided ftrace location\n"); > return ret;
This must be -EBUSY. (or arch depend return value)
> + } > jump_label_lock(); > preempt_disable(); > > @@ -1552,6 +1554,7 @@ static int check_kprobe_address_safe(struct kprobe *p, > within_kprobe_blacklist((unsigned long) p->addr) || > jump_label_text_reserved(p->addr, p->addr) || > find_bug((unsigned long)p->addr)) { > + pr_err("kprobes: can't probe at address in reject list\n"); > ret = -EINVAL;
This maybe -EACCESS.
> goto out; > } > @@ -1976,8 +1979,10 @@ int register_kretprobe(struct kretprobe *rp) > void *addr; > > ret = kprobe_on_func_entry(rp->kp.addr, rp->kp.symbol_name, rp->kp.offset); > - if (ret) > + if (ret) { > + pr_err("kretprobes: can't probe at address outside function entry\n"); > return ret;
return -ERANGE.
> + } > > /* If only rp->kp.addr is specified, check reregistering kprobes */ > if (rp->kp.addr && warn_kprobe_rereg(&rp->kp)) > @@ -1989,8 +1994,10 @@ int register_kretprobe(struct kretprobe *rp) > return PTR_ERR(addr); > > for (i = 0; kretprobe_blacklist[i].name != NULL; i++) { > - if (kretprobe_blacklist[i].addr == addr) > + if (kretprobe_blacklist[i].addr == addr) { > + pr_err("kretprobes: can't probe at address in reject list\n"); > return -EINVAL;
return -EACCESS too.
Thank you,
> + } > } > } > > > base-commit: 2e38eb04c95e5546b71bb86ee699a891c7d212b5 > -- > 2.31.1 >
-- Masami Hiramatsu <mhiramat@kernel.org>
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