linux-kernel - Re: [RFC PATCH 2/7] x86/sci: add core implementation for system call isolation

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Message-ID: <20190426095802.GA35515@gmail.com>
Date:   Fri, 26 Apr 2019 11:58:02 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Jonathan Adams <jwadams@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Paul Turner <pjt@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, linux-mm@...ck.org,
        linux-security-module@...r.kernel.org, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 2/7] x86/sci: add core implementation for system call
 isolation


* Ingo Molnar <mingo@...nel.org> wrote:

> I really don't like it where this is going. In a couple of years I 
> really want to be able to think of PTI as a bad dream that is mostly 
> over fortunately.
> 
> I have the feeling that compiler level protection that avoids 
> corrupting the stack in the first place is going to be lower overhead, 
> and would work in a much broader range of environments. Do we have 
> analysis of what the compiler would have to do to prevent most ROP 
> attacks, and what the runtime cost of that is?
> 
> I mean, C# and Java programs aren't able to corrupt the stack as long 
> as the language runtime is corect. Has to be possible, right?

So if such security feature is offered then I'm afraid distros would be 
strongly inclined to enable it - saying 'yes' to a kernel feature that 
can keep your product off CVE advisories is a strong force.

To phrase the argument in a bit more controversial form:

   If the price of Linux using an insecure C runtime is to slow down 
   system calls with immense PTI-alike runtime costs, then wouldn't it be 
   the right technical decision to write the kernel in a language runtime 
   that doesn't allow stack overflows and such?

I.e. if having Linux in C ends up being slower than having it in Java, 
then what's the performance argument in favor of using C to begin with? 
;-)

And no, I'm not arguing for Java or C#, but I am arguing for a saner 
version of C.

Thanks,

	Ingo