linux-kernel - Re: Question: livepatch failed for new fork() task stack unreliable

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Date:   Fri, 5 Jun 2020 09:26:42 +0800
From:   "Wangshaobo (bobo)" <bobo.shaobowang@...wei.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
CC:     <huawei.libin@...wei.com>, <xiexiuqi@...wei.com>,
        <cj.chengjian@...wei.com>, <mingo@...hat.com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <live-patching@...r.kernel.org>,
        <mbenes@...e.cz>, <devel@...ukata.com>, <viro@...iv.linux.org.uk>,
        <esyr@...hat.com>
Subject: Re: Question: livepatch failed for new fork() task stack unreliable


在 2020/6/4 10:40, Josh Poimboeuf 写道:
> On Thu, Jun 04, 2020 at 09:24:55AM +0800, Wangshaobo (bobo) wrote:
>> 在 2020/6/3 23:33, Josh Poimboeuf 写道:
>>> On Wed, Jun 03, 2020 at 10:06:07PM +0800, Wangshaobo (bobo) wrote:
>>> To be honest, I don't remember what I meant by sibling calls.  They
>>> don't even leave anything on the stack.
>>>
>>> For noreturns, the code might be laid out like this:
>>>
>>> func1:
>>> 	...
>>> 	call noreturn_foo
>>> func2:
>>>
>>> func2 is immediately after the call to noreturn_foo.  So the return
>>> address on the stack will actually be 'func2'.  We want to retrieve the
>>> ORC data for the call instruction (inside func1), instead of the
>>> instruction at the beginning of func2.
>>>
>>> I should probably update that comment.
>> So, I want to ask is there any side effects if i modify like this ? this
>> modification is based on
>>
>> your fix. It looks like ok with proper test.
>>
>> diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
>> index e9cc182aa97e..ecce5051e8fd 100644
>> --- a/arch/x86/kernel/unwind_orc.c
>> +++ b/arch/x86/kernel/unwind_orc.c
>> @@ -620,6 +620,7 @@ void __unwind_start(struct unwind_state *state, struct
>> task_struct *task,
>>                  state->sp = task->thread.sp;
>>                  state->bp = READ_ONCE_NOCHECK(frame->bp);
>>                  state->ip = READ_ONCE_NOCHECK(frame->ret_addr);
>> +              state->signal = ((void *)state->ip == ret_from_fork);
>>          }
>>
>> diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
>> index 7f969b2d240f..d7396431261a 100644
>> --- a/arch/x86/kernel/unwind_orc.c
>> +++ b/arch/x86/kernel/unwind_orc.c
>> @@ -540,7 +540,7 @@ bool unwind_next_frame(struct unwind_state *state)
>>           state->sp = sp;
>>           state->regs = NULL;
>>           state->prev_regs = NULL;
>> -        state->signal = ((void *)state->ip == ret_from_fork);
>> +        state->signal = false;
>>           break;
> Yes that's correct.

Hi, josh

Could i ask when are you free to send the patch, all the tests are 
passed by.

thanks for your help.

Wang ShaoBo

>