linux-kernel - Re: [RFC 0/4] Fix machine check recovery for copy_from

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Date:   Fri, 9 Apr 2021 14:49:09 +0800
From:   Aili Yao <yaoaili@...gsoft.com>
To:     "Luck, Tony" <tony.luck@...el.com>
CC:     Borislav Petkov <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andy Lutomirski <luto@...nel.org>,
        "HORIGUCHI NAOYA( 堀口　直也)" 
        <naoya.horiguchi@....com>, <yaoaili@...gsoft.com>
Subject: Re: [RFC 0/4] Fix machine check recovery for copy_from_user

On Thu, 8 Apr 2021 14:39:09 +0000
"Luck, Tony" <tony.luck@...el.com> wrote:

> > I have one scenario, may you take into account:
> >
> > If one copyin case occurs, write() returned by your patch, the user process may
> > check the return values, for errors, it may exit the process, then the error page
> > will be freed, and then the page maybe alloced to other process or to kernel itself,
> > then code will initialize it and this will trigger one SRAO, if it's used by kernel,
> > we may do nothing for this, and kernel may still touch it, and lead to one panic.  
> 
> In this case kill_me_never() calls memory_failure() with flags == 0. I think (hope!)
> that means that it will unmap the page from the task, but will not send a signal.
> 
> When the task exits the PTE for this page has the swap/poison signature, so the
> page is not freed for re-use.
> 
> -Tony

Oh, Yes, Sorry for my rudeness and error-understandings, I just happen to can't control my emotions and get confused for some other things.

Thanks!
Aili Yao