netdev - Re: [PATCH][v4] uprobes/x86: emulate push insns for uprobe on x86

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Message-ID: <b3b59c8a-494f-51ed-2691-c4c544e771a1@fb.com>
Date:   Mon, 20 Nov 2017 10:25:55 -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][v4] uprobes/x86: emulate push insns for uprobe on x86



On 11/20/17 8:41 AM, Oleg Nesterov wrote:
> On 11/17, Yonghong Song wrote:
>>
>> On 11/17/17 9:25 AM, Oleg Nesterov wrote:
>>> On 11/15, Yonghong Song wrote:
>>>>
>>>> v3 -> v4:
>>>>    . Revert most of v3 change as 32bit emulation is not really working
>>>>      on x86_64 platform as among other issues, function emulate_push_stack()
>>>>      needs to account for 32bit app on 64bit platform.
>>>>      A separate effort is ongoing to address this issue.
>>>
>>> Reviewed-by: Oleg Nesterov <oleg@...hat.com>
>>>
>>>
>>>
>>> Please test your patch with the fix below, in this particular case the
>>> TIF_IA32 check should be fine. Although this is not what we really want,
>>> we should probably use user_64bit_mode(regs) which checks ->cs. But this
>>> needs more changes and doesn't solve other problems (get_unmapped_area)
>>> so I still can't decide what should we do right now...
>>
>> I tested the below change with my patch. On x86_64, both 64bit and 32bit
>> program can be uprobe emulated properly.
> 
> Good, so your patch is fine.

Thanks!

> 
>> On x86_32, however, there is a
>> compilation error like below:
> 
> Yes, yes, when I said "in this particular case" I meant x86_64 system only.
> 
> Sorry for confusion, I asked you to test this additional change just to
> ensure that we didn't miss something and your patch has no problems with
> 32bit tasks on 64bit system, except those we need to fix anyway.

Understood. I actually tried a little to see whether I could have a 
simple way to fix 32bit compilation error without using ugly "#ifdef 
CONFIG_X86_64". Maybe is_64bit_mm is a good choice. But we could defer 
this until you have a comprehensive fix for 32bit app uprobe on 64bit 
systems as there are multiple issues for this.

> 
> Oleg.
>