Re: [PATCH][kprobes] support kretprobe-blacklist

[Masami Hiramatsu]

Hi Andrew,

Thank you for comments.

Andrew Morton wrote:
>> Index: 2.6-mm/include/asm-i386/kprobes.h
>> ===================================================================
>> --- 2.6-mm.orig/include/asm-i386/kprobes.h
>> +++ 2.6-mm/include/asm-i386/kprobes.h
>> @@ -44,6 +44,7 @@ typedef u8 kprobe_opcode_t;
>>
>>  #define ARCH_SUPPORTS_KRETPROBES
>>  #define flush_insn_slot(p)	do { } while (0)
>> +#define ARCH_SUPPORTS_KRETPROBE_BLACKLIST
> 
> Can we avoid adding this please?

Yes, sure. I'll update my patch and eliminate those ifdefs.

> It should at least have been a CONFIG_foo thing, defined in arch/*/Kconfig.
> 
> But that still requires nasty ifdefs in the C code.  It would be very small
> overhead just to require that all architectures implement
> arch_kretprobe_blacklist[] (which can be renamed to kretprobe_blacklist[]).
>  Architectures which don't need a blacklist can just have { { 0, 0 } }.
> 
> If the few bytes of overhead on non-x86 really offends then one could do
> something like this:
> 
> in powerpc header file:
> 
> #define kretprobe_blacklist_size 0
> 
> in x86 header file:
> 
> extern const int kretprobe_blacklist_size;
> 
> in x86 C file:
> 
> const int kretprobe_blacklist_size = ARRAY_SIZE(kretprobe_blacklist);

It's looks very nice, thank you for the advice.
I think we can directly define "kretprobe_blacklist" as 0 in (for
example)ppc header instead of introducing "kretprobe_blacklist_size",
and check if "kretprobe_blacklist" is 0 or not in common code, is it OK?

> and then this code:
> 
>> --- 2.6-mm.orig/kernel/kprobes.c
>> +++ 2.6-mm/kernel/kprobes.c
>> @@ -716,6 +716,18 @@ int __kprobes register_kretprobe(struct
>>  	int ret = 0;
>>  	struct kretprobe_instance *inst;
>>  	int i;
>> +#ifdef ARCH_SUPPORTS_KRETPROBE_BLACKLIST
>> +	void *addr = rp->kp.addr;
>> +
>> +	if (addr == NULL)
>> +		kprobe_lookup_name(rp->kp.symbol_name, addr);
>> +	addr += rp->kp.offset;
>> +
>> +	for (i = 0; arch_kretprobe_blacklist[i].name != NULL; i++) {
>> +		if (arch_kretprobe_blacklist[i].addr == addr)
>> +			return -EINVAL;
>> +	}
>> +#endif
> 
> can be put inside
> 
> 	if (kretprobe_blacklist_size) {
> 		...
> 	}
> 
> so the compiler will remove it all for (say) powerpc.
>
> There are lots of ways of doing it but code like this:
> 
>> +#ifdef ARCH_SUPPORTS_KRETPROBE_BLACKLIST
>> +	/* lookup the function address from its name */
>> +	for (i = 0; arch_kretprobe_blacklist[i].name != NULL; i++) {
>> +		kprobe_lookup_name(arch_kretprobe_blacklist[i].name,
>> +				   arch_kretprobe_blacklist[i].addr);
>> +		if (!arch_kretprobe_blacklist[i].addr)
>> +			printk("kretprobe: Unknown blacklisted function: %s\n",
>> +			       arch_kretprobe_blacklist[i].name);
>> +	}
>> +#endif
> 
> really isn't the sort of thing we like to see spreading through core kernel
> code.
> 
> Have a think about it please, see what we can come up with?

OK, I see. I'll do that next time.

Best regards,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@xxxxxxxxxx, masami.hiramatsu.pt@xxxxxxxxxxx
Tel: +1-978-392-2419
Tel: +1-508-982-2642 (cell phone)
Fax: +1-978-392-1001
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