Re: [PATCH v11 8/9] arm64: Add kernel return probes support (kretprobes)

From: David Long <dave.long@linaro.org>
To: "平松雅巳 / HIRAMATU，MASAMI" <masami.hiramatsu.pt@hitachi.com>,
	"'ltc-kernel@ml.yrl.intra.hitachi.co.jp'"
	<ltc-kernel@ml.yrl.intra.hitachi.co.jp>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Will Deacon" <will.deacon@arm.com>,
	"Sandeepa Prabhu" <sandeepa.s.prabhu@gmail.com>,
	"William Cohen" <wcohen@redhat.com>,
	"Pratyush Anand" <panand@redhat.com>,
	"Steve Capper" <steve.capper@linaro.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Marc Zyngier" <marc.zyngier@arm.com>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
	"Petr Mladek" <pmladek@suse.com>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"John Blackwood" <john.blackwood@ccur.com>,
	"Feng Kan" <fkan@apm.com>, "Zi Shen Lim" <zlim.lnx@gmail.com>,
	"Dave P Martin" <Dave.Martin@arm.com>,
	"Yang Shi" <yang.shi@linaro.org>,
	"Vladimir Murzin" <Vladimir.Murzin@arm.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Suzuki K. Poulose" <suzuki.poulose@arm.com>,
	"Mark Brown" <broonie@kernel.org>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Mark Salyzyn" <salyzyn@android.com>,
	"James Morse" <james.morse@arm.com>,
	"Christoffer Dall" <christoffer.dall@linaro.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Robin Murphy" <Robin.Murphy@arm.com>,
	"Jens Wiklander" <jens.wiklander@linaro.org>,
	"Balamurugan Shanmugam" <bshanmugam@apm.com>,
	sysp-manager <cti.systems-productivity-manager.ts@hitachi.com>
Subject: Re: [PATCH v11 8/9] arm64: Add kernel return probes support (kretprobes)
Date: Mon, 21 Mar 2016 09:33:51 -0400	[thread overview]
Message-ID: <56EFF83F.7040906@linaro.org> (raw)
In-Reply-To: <50399556C9727B4D88A595C8584AAB37B4E504AA@GSjpTKYDCembx32.service.hitachi.net>

On 03/17/2016 08:58 AM, 平松雅巳 / HIRAMATU，MASAMI wrote:
>> From: 平松雅巳 / HIRAMATU，MASAMI [mailto:masami.hiramatsu.pt@hitachi.com]
>>
>> Hi,
>>
>>> From: Sandeepa Prabhu <sandeepa.s.prabhu@gmail.com>
>>>
>>> The pre-handler of this special 'trampoline' kprobe executes the return
>>> probe handler functions and restores original return address in ELR_EL1.
>>> This way the saved pt_regs still hold the original register context to be
>>> carried back to the probed kernel function.
>>
>> This patch seems not well separated.
>>
>>> diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
>>> index bd3f233..13d3333 100644
>>> --- a/arch/arm64/kernel/kprobes.c
>>> +++ b/arch/arm64/kernel/kprobes.c
>>
>> [snip]
>>
>>> +void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
>>> +				      struct pt_regs *regs)
>>> +{
>>> +	ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
>>> +
>>> +	/* replace return addr (x30) with trampoline */
>>> +	regs->regs[30] = (long)&kretprobe_trampoline;
>>
>> So, where is the kretprobe_trampoline? It seems that function is
>> defined in other patch.
>>
>>> +}
>>> +
>>> +int __kprobes arch_trampoline_kprobe(struct kprobe *p)
>>> +{
>>> +	return 0;
>>> }
>>
>> And what this function is for??
>
> Ah, sorry, this was my fault. Yes, this function is required.
> But this implementation also means there is an asm-based trampoline
> function which should be included in this patch.
>
> David, could you tell me the repository which I can get the latest
> version of this series? I'd like to see the whole code of kprobes/arm64.
>
> Thank you,
>

It can be found in:

http://git.linaro.org/people/dave.long/linux.git

...in the kprobes64-v11 branch.

Thanks,
-dl