linux-kernel - Re: [PATCH][v2] uprobes/x86: emulate push insns for uprobe on x86

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Message-ID: <cd34cc94-94ff-dd79-5f0e-c6b1bfb99126@fb.com>
Date:   Tue, 14 Nov 2017 14:22:46 -0800
From:   Yonghong Song <yhs@...com>
To:     Oleg Nesterov <oleg@...hat.com>
CC:     <mingo@...nel.org>, <tglx@...utronix.de>, <peterz@...radead.org>,
        <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        <netdev@...r.kernel.org>, <ast@...com>, <kernel-team@...com>
Subject: Re: [PATCH][v2] uprobes/x86: emulate push insns for uprobe on x86



On 11/14/17 7:34 AM, Oleg Nesterov wrote:
> On 11/13, Yonghong Song wrote:
>>
>> On 11/13/17 4:59 AM, Oleg Nesterov wrote:
>>>> +		switch (opc1) {
>>>> +		case 0x50:
>>>> +			reg_offset = offsetof(struct pt_regs, r8);
>>>> +			break;
>>>> +		case 0x51:
>>>> +			reg_offset = offsetof(struct pt_regs, r9);
>>>> +			break;
>>>> +		case 0x52:
>>>> +			reg_offset = offsetof(struct pt_regs, r10);
>>>> +			break;
>>>> +		case 0x53:
>>>> +			reg_offset = offsetof(struct pt_regs, r11);
>>>> +			break;
>>>> +		case 0x54:
>>>> +			reg_offset = offsetof(struct pt_regs, r12);
>>>> +			break;
>>>> +		case 0x55:
>>>> +			reg_offset = offsetof(struct pt_regs, r13);
>>>> +			break;
>>>> +		case 0x56:
>>>> +			reg_offset = offsetof(struct pt_regs, r14);
>>>> +			break;
>>>> +		case 0x57:
>>>> +			reg_offset = offsetof(struct pt_regs, r15);
>>>> +			break;
>>>> +		}
>>>> +#else
>>>> +		return -ENOSYS;
>>>> +#endif
>>>
>>> OK, but shouldn't we also return ENOSYS if CONFIG_X86_64=y but the probed task is 32bit?
>>
>> Just tested with a 32bit app on x86 box and segfaults.
> 
> Hmm. How did you verify this?

On a x86_32 box, I compiled the test case with static libraries 
(including static libc). And I then run this binary on x86_64 with
uprobe enabled. You will need to install glibc-static package to make it 
work.

> 
> Your v3 doesn't look right and it seems you misunderstood me...
> 
>> Yes, we would need to
>> return ENOSYS if the app is 32bit on 64bit system.
> 
> Only if insn->length == 2. "push bp" and other valid 32bit push'es should be
> emulated correctly or your patch is wrong. Confused... >
>>> Or in this case uprobe_init_insn(x86_64 => false) should fail and push_setup_xol_ops()
>>> won't be called?
> 
> So it doesn't fail?
> 
> Oleg.
>