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Date: Tue, 11 Sep 2018 09:01:02 -0700
From: Kristen C Accardi <kristen@...ux.intel.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: kernel-hardening@...ts.openwall.com
Subject: Re: [RFC PATCH] x86: entry: flush the cache if syscall error
On Tue, 2018-09-11 at 10:41 +0200, Greg KH wrote:
> On Mon, Sep 10, 2018 at 12:10:02PM -0700, Kristen Carlson Accardi
> wrote:
> > This patch aims to make it harder to perform cache timing attacks
> > on data
> > left behind by system calls. If we have an error returned from a
> > syscall,
> > flush the L1 cache.
> >
> > Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> > ---
> > arch/x86/Kconfig | 8 ++++++++
> > arch/x86/entry/common.c | 20 ++++++++++++++++++++
> > 2 files changed, 28 insertions(+)
> >
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index c5ff296bc5d1..8a67642ff9fe 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -445,6 +445,14 @@ config RETPOLINE
> > code are eliminated. Since this includes the syscall
> > entry path,
> > it is not entirely pointless.
> >
> > +config SYSCALL_FLUSH
> > + bool "Clear L1 Cache on syscall errors"
> > + default y
>
> "y" normally is only for "your machine will not boot without this
> option", and I don't think that's the case here :)
true. :). I wish there was a way to indicate that this option provided
enhanced security so that people could just select all of these
features at once and I could make it select based on that option.
>
> > + help
> > + Select to allow the L1 cache to be cleared upon return
> > of
> > + an error code from a syscall. This will reduce the
> > likelyhood of
> > + speculative execution style attacks on syscalls.
>
> Shouldn't this help text refer to the fact that this needs CPU
> support
> for this type of functionality?
OK, I will change it.
>
> I like the idea, as a "gadget" normally only is used when an
> out-of-bands check happens, which implies someone could be trying to
> do
> something "bad", nice job.
>
> thanks,
>
> greg k-h
Thanks!
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