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

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Date:   Thu, 4 Jun 2020 09:24:55 +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 2020/6/3 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;

thanks,

Wang ShaoBo