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Date: Tue, 11 Sep 2018 10:41:48 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc: kernel-hardening@...ts.openwall.com
Subject: Re: [RFC PATCH] x86: entry: flush the cache if syscall error
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 :)
> + 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?
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
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