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Subject: Re: [RFC PATCH 0/7] x86: introduce system calls addess space
 isolation
To:     Mike Rapoport <rppt@linux.ibm.com>, linux-kernel@vger.kernel.org
Cc:     Alexandre Chartre <alexandre.chartre@oracle.com>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        Jonathan Adams <jwadams@google.com>,
        Kees Cook <keescook@chromium.org>,
        Paul Turner <pjt@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>, linux-mm@kvack.org,
        linux-security-module@vger.kernel.org, x86@kernel.org
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From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <1c12e195-1286-0136-eae5-4b392d9fe4c0@intel.com>
Date:   Fri, 26 Apr 2019 07:41:09 -0700
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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?