linux-kernel - Re: [RFC PATCH 0/7] x86: introduce system calls addess space isolation

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Date:   Fri, 26 Apr 2019 07:41:09 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>, linux-kernel@...r.kernel.org
Cc:     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
Subject: Re: [RFC PATCH 0/7] x86: introduce system calls addess space
 isolation

On 4/25/19 2:45 PM, Mike Rapoport wrote:
> The idea behind the prevention is that if we fault in pages in the
> execution path, we can compare target address against the kernel symbol
> table.  So if we're in a function, we allow local jumps (and simply falling
> of the end of a page) but if we're jumping to a new function it must be to
> an external label in the symbol table.  Since ROP attacks are all about
> jumping to gadget code which is effectively in the middle of real
> functions, the jumps they induce are to code that doesn't have an external
> symbol, so it should mostly detect when they happen.

This turns the problem from: "attackers can leverage any data/code that
the kernel has mapped (anything)" to "attackers can leverage any
code/data that the current syscall has faulted in".

That seems like a pretty restrictive change.

> At this time we are not suggesting any API that will enable the system
> calls isolation. Because of the overhead required for this, it should only
> be activated for processes or containers we know should be untrusted. We
> still have no actual numbers, but surely forcing page faults during system
> call execution will not come for free.

What's the minimum number of faults that have to occur to handle the
simplest dummy fault?