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Message-ID: <202007091634.528B6641@keescook>
Date: Thu, 9 Jul 2020 16:37:37 -0700
From: Kees Cook <keescook@...omium.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>,
"Andersen, John" <john.s.andersen@...el.com>,
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Subject: Re: [PATCH 2/4] KVM: x86: Introduce paravirt feature CR0/CR4 pinning
On Thu, Jul 09, 2020 at 09:22:09AM -0700, Dave Hansen wrote:
> On 7/9/20 9:07 AM, Andy Lutomirski wrote:
> > On Thu, Jul 9, 2020 at 8:56 AM Dave Hansen <dave.hansen@...el.com> wrote:
> >> On 7/9/20 8:44 AM, Andersen, John wrote:
> >>> Bits which are allowed to be pinned default to WP for CR0 and SMEP,
> >>> SMAP, and UMIP for CR4.
> >> I think it also makes sense to have FSGSBASE in this set.
> >>
> >> I know it hasn't been tested, but I think we should do the legwork to
> >> test it. If not in this set, can we agree that it's a logical next step?
> > I have no objection to pinning FSGSBASE, but is there a clear
> > description of the threat model that this whole series is meant to
> > address? The idea is to provide a degree of protection against an
> > attacker who is able to convince a guest kernel to write something
> > inappropriate to CR4, right? How realistic is this?
>
> If a quick search can find this:
>
> > https://googleprojectzero.blogspot.com/2017/05/exploiting-linux-kernel-via-packet.html
>
> I'd pretty confident that the guys doing actual bad things have it in
> their toolbox too.
Right, it's common (see my commit log in 873d50d58f67), and having this
enforced by the hypervisor is WAY better since it'll block gadgets or
ROP.
--
Kees Cook
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