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Subject: Re: [PATCH 00/10] Control Flow Enforcement - Part (3)
From:   Balbir Singh <bsingharora@gmail.com>
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc:     linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-mm@kvack.org, linux-arch@vger.kernel.org, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H.J. Lu" <hjl.tools@gmail.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Jonathan Corbet <corbet@lwn.net>,
        Oleg Nesterov <oleg@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
        Mike Kravetz <mike.kravetz@oracle.com>
Date:   Sun, 17 Jun 2018 13:16:02 +1000
In-Reply-To: <1528988176.13101.15.camel@2b52.sc.intel.com>
References: <20180607143807.3611-1-yu-cheng.yu@intel.com>
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         <1528815820.8271.16.camel@2b52.sc.intel.com>
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On Thu, 2018-06-14 at 07:56 -0700, Yu-cheng Yu wrote:
> On Thu, 2018-06-14 at 11:07 +1000, Balbir Singh wrote:
> > On Tue, 2018-06-12 at 08:03 -0700, Yu-cheng Yu wrote:
> > > On Tue, 2018-06-12 at 20:56 +1000, Balbir Singh wrote:
> > > > 
> > > > On 08/06/18 00:37, Yu-cheng Yu wrote:
> > > > > This series introduces CET - Shadow stack
> > > > > 
> > > > > At the high level, shadow stack is:
> > > > > 
> > > > > 	Allocated from a task's address space with vm_flags VM_SHSTK;
> > > > > 	Its PTEs must be read-only and dirty;
> > > > > 	Fixed sized, but the default size can be changed by sys admin.
> > > > > 
> > > > > For a forked child, the shadow stack is duplicated when the next
> > > > > shadow stack access takes place.
> > > > > 
> > > > > For a pthread child, a new shadow stack is allocated.
> > > > > 
> > > > > The signal handler uses the same shadow stack as the main program.
> > > > > 
> > > > 
> > > > Even with sigaltstack()?
> > > > 
> > > 
> > > Yes.
> > 
> > I am not convinced that it would work, as we switch stacks, oveflow might
> > be an issue. I also forgot to bring up setcontext(2), I presume those
> > will get new shadow stacks
> 
> Do you mean signal stack/sigaltstack overflow or swapcontext in a signal
> handler?
>

I meant any combination of that. If there is a user space threads implementation that uses sigaltstack for switching threads

Balbir Singh.
 
> Yu-cheng
>