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Subject: Re: [RFC PATCH 2/7] x86/sci: add core implementation for system
 call isolation
From:   James Bottomley <James.Bottomley@HansenPartnership.com>
To:     Dave Hansen <dave.hansen@intel.com>,
        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>,
        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
Date:   Fri, 26 Apr 2019 07:57:38 -0700
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On Fri, 2019-04-26 at 07:46 -0700, Dave Hansen wrote:
> On 4/25/19 2:45 PM, Mike Rapoport wrote:
> > After the isolated system call finishes, the mappings created
> > during its execution are cleared.
> 
> Yikes.  I guess that stops someone from calling write() a bunch of
> times on every filesystem using every block device driver and all the
> DM code to get a lot of code/data faulted in.  But, it also means not
> even long-running processes will ever have a chance of behaving
> anything close to normally.
> 
> Is this something you think can be rectified or is there something
> fundamental that would keep SCI page tables from being cached across
> different invocations of the same syscall?

There is some work being done to look at pre-populating the isolated
address space with the expected execution footprint of the system call,
yes.  It lessens the ROP gadget protection slightly because you might
find a gadget in the pre-populated code, but it solves a lot of the
overhead problem.

James